Time for an overhaul...

[thebeebe5]

On 11/15/2019 at 11:50 PM, Andydodge said:

Beebe......I too have just reread the entire thread and still get info and enjoyment out of it............its 12 months since your last post, how have things panned out re the engine rebuild and the possible turbo install?...........I trust you are going o/k and again thanks for all the effort in posting this thread......regards from Oz.........andyd  

 

Thanks everyone, and  thanks for the kind words, Andy.  Forgive the tardy response.   I’ve become very busy at my regular job and even more involved at the shop and I forget to check in.... ?

 

Not sure how many miles I have on the motor now, but I can look.  It’s running like a top.  Retaining the old lifters created a bit more work in repeated valve lashings until I got it where I wanted it.  The turbo is still sitting on the bench where I left it.... ?....  Brian keeps bugging me about “let’s force induct a ‘37 coupe today” when I arrive on Saturdays, but there’s a little work I need to complete first.   The cylinder head either developed a small crack or I missed it when we magged it away back when....   over the piston between #4 and #5.   It’s a small one....  maybe 0.5-0.75” long.   With the non pressure system it really doesn’t leak anything, but it made an ugly rust stain right there for everyone to see.    I want to pull it, braze it up and reinstall before I try forcing extra air down the car’s throat. 

 

Oil pressure cold is still 60 psi, decreases to 50 at hot cruise, 12-15 psi at idle (factory gauge, so kind of guessing on the low end.  Max matched the gauge we used when we drill-spun to oil prime prior to install.   Water temp goes to 180° and stays there even in 115° weather.   Trans howls a bit.  I’ve been collecting NOS parts to do it again and have everything except a cluster and 1/R.  I hesitated on a cluster 1st/Reverse set early in the year and missed out.   The available NOS ones on ebay are ridiculously priced.    It can howl all it wants, but I’ll not shell out $400 for a cluster gear.  

 

Still looks good, still gets complements at cruises.   Old timers love that I pull in (after a long day at the shop) in a 6v coupe with its original flatty.   One guy walked by and asked if I’d mind starting it for him so he could listen.  

 

I said   “bend your ear over here, Mister...  it’s running now”   

 

That night I smiled all the way home. 

 

[kencombs]

Glad to hear feedback on the oil pressure.  I've been debating the full flow mod as you did it.  Sounds like the hole placement and line sizing has been proven in your use.  Now, just to get up the nerve to drill/tap my block.

[T120]

the beebe5, Good thread.Thanks. A job well done!

[pflaming]

I too, just read this thread. I started this hobby some 10+/- years ago and realize that I’m now in the advanced novice stage. Yet it is an enjoyable experience. I only knew how to change oil and plugs when I started. To those who have helped teach me, thanks. 

[thebeebe5]

On 3/7/2020 at 9:17 AM, T120 said:

the beebe5, Good thread.Thanks. A job well done!

 

20 hours ago, pflaming said:

I too, just read this thread. I started this hobby some 10+/- years ago and realize that I’m now in the advanced novice stage. Yet it is an enjoyable experience. I only knew how to change oil and plugs when I started. To those who have helped teach me, thanks. 

Thanks fellows.  People that love the hobby share knowledge that furthers the hobby.  I’m always happy to answer questions.  
 

My pal Brian (that owns the machine shop I spend my weekends in) selflessly offers advice and technical knowledge.   I’ve built an MG Midget 1500, an FE big block Ford and the Plymouth flat 6 chronicled here and disassembled more engines than I can remember all while learning.   From reading bearing wear to assessing parts for reuse to tuning the single Carter found on my Plymouth to tuning a phalanx of Weber 48IDAs found on a Ford GT40 Mirage....  

All this from an enthusiast that loves to share knowledge.  
I’ll keep passing it on.  I’m currently inflicting knowledge on my 19 year old son.  My Pop started me much earlier, but I’m thrilled my boy found a classic that turned him on and thrilled he wants to learn. 
 

[Matt Wilson]

Hi Jim,

 

I've been doing searches to find out more about custom pistons and modern rings, and I came across this thread again (I read it a few years ago too)  Still a great thread!  I see that you ordered custom pistons from JE Pistons and used modern thinner rings.  I'm interested in doing the same thing for my engine (a 265).  I'm interested in doing this for durability and longevity reasons.  It seems that our flatheads often suffer ring and cylinder wear prematurely compared to modern engines, sometimes accompanied by ring and ring land breakage (usually after 75,000 - 100,000 miles, I realize, but still, if I can do something to fend that off, I'd like to).  So I'm wondering...how has your engine held up?  How many miles have you put on it?  Are you satisfied with the performance of the pistons and the rings?  Any oddities or deficiencies with the compression or power output?  Any oil burning beyond what you'd normally expect in an engine like this?  How do the spark plugs look?  Any signs of blow-by or premature dirtying of the oil? If you had to do it again, would you take this route, or other custom pistons, or just use original-style pistons?  Are there any other things you would caution me about?

 

I see that JE has a custom piston order form.  I don't know what some of the terms mean (like spin boss, accumulator grooves, contact reduction, etc.), but if their technical rep will walk me through it, I'm sure I can get what I need.  I've never ordered custom pistons or tried to substitute different rings in an engine before. 

 

Looking at articles on thin/low-tension rings, it seems that there are a LOT of considerations and questions, most of which I don't have answers for, and the articles make it sound like you really need to know what you're doing and be prepared to experiment a lot, but I have a feeling those articles are geared toward racing applications, where folks are really tricking out their engines and trying to squeeze every last drop of power out them.  There are considerations about gas ports, compression heights, ring coatings and many other details, but again, maybe these are not such an issue for a mildly hopped up street engine.  How did you decide on these aspects? 

 

Of course, in talking with others, I've come to realize that modern production engine rings are not necessarily low-tension rings.  I had just figured they were, since they are lower tension than the ones originally used in our engines.  I'm a bit nervous when it comes to ordering something that will work well, but maybe it's not a big deal, and just a matter of buying rings for a modern reliable engine from a reliable ring supplier and let the piston supplier figure out some of the details.

 

Any advice you can offer would be appreciated.  I'd really like to do this, but if there is anything risky about it, I might avoid it.

Edited January 22, 2022 by Matt Wilson

[thebeebe5]

16 hours ago, Matt Wilson said:

Hi Jim,

 

I've been doing searches to find out more about custom pistons and modern rings, and I came across this thread again (I read it a few years ago too)  Still a great thread!  I see that you ordered custom pistons from JE Pistons and used modern thinner rings.  I'm interested in doing the same thing for my engine (a 265).  I'm interested in doing this for durability and longevity reasons.  It seems that our flatheads often suffer ring and cylinder wear prematurely compared to modern engines, sometimes accompanied by ring and ring land breakage (usually after 75,000 - 100,000 miles, I realize, but still, if I can do something to fend that off, I'd like to).  So I'm wondering...how has your engine held up?  How many miles have you put on it?  Are you satisfied with the performance of the pistons and the rings?  Any oddities or deficiencies with the compression or power output?  Any oil burning beyond what you'd normally expect in an engine like this?  How do the spark plugs look?  Any signs of blow-by or premature dirtying of the oil? If you had to do it again, would you take this route, or other custom pistons, or just use original-style pistons?  Are there any other things you would caution me about?

 

I see that JE has a custom piston order form.  I don't know what some of the terms mean (like spin boss, accumulator grooves, contact reduction, etc.), but if their technical rep will walk me through it, I'm sure I can get what I need.  I've never ordered custom pistons or tried to substitute different rings in an engine before. 

 

Looking at articles on thin/low-tension rings, it seems that there are a LOT of considerations and questions, most of which I don't have answers for, and the articles make it sound like you really need to know what you're doing and be prepared to experiment a lot, but I have a feeling those articles are geared toward racing applications, where folks are really tricking out their engines and trying to squeeze every last drop of power out them.  There are considerations about gas ports, compression heights, ring coatings and many other details, but again, maybe these are not such an issue for a mildly hopped up street engine.  How did you decide on these aspects? 

 

Of course, in talking with others, I've come to realize that modern production engine rings are not necessarily low-tension rings.  I had just figured they were, since they are lower tension than the ones originally used in our engines.  I'm a bit nervous when it comes to ordering something that will work well, but maybe it's not a big deal, and just a matter of buying rings for a modern reliable engine from a reliable ring supplier and let the piston supplier figure out some of the details.

 

Any advice you can offer would be appreciated.  I'd really like to do this, but if there is anything risky about it, I might avoid it.

Matt.   Glad you found the thread informative.   
 

Lots of good questions here.  I’ll answer as best I can.  
 

Regarding your first comment related to premature wear, consider 75,000-100,000 was a respectable accumulation back in the day.   Oil wasn’t anywhere near what it is now. Our motors get far better protection with lubricants available today, and we aren’t even considering filtration (or lack thereof).  Also something to consider is a proper tune.  A really rich AFR pouring too much fuel into the chamber (even these days) is a sure way to wear rings and cylinder walls, contaminate oil and speed premature failure.  Cold weather dwellers that fired their car up with the choke on full and went back into the house to make breakfast while the car warmed up weren’t doing themselves any long-term favors.   All can lead to ring and cylinder wall wear.   This wear certainly wasn’t due to inferior materials. Foundries were making better iron back then than much of the imported stuff now. 
 

I’ve not had any issues with the engine related to compression or blow by.  I did find a crack in the head that I fixed a little over a year ago that was either missed when I Magnafluxed it or developed after the build. I don’t recall if I covered that repair here or not, but while the head was off we had a good look at the cylinder walls and they looked as if they’d just been honed.  The oil looked clean with minimal contamination when I did my first oil change after rebuild.   Could easily see through it though as expected it did darken in that time. I’d do the same thing again (but not with JE) to save cylinder wall thickness.  We only honed until the cylinders cleaned/squared up rather than going up in full 0.010” increments.  No visible oil burning at all.  A far cry from the pre-build smoke screen.  Car has excellent power.  I can accelerate from 3rd gear at 20mph up an over-pass with ease.   No issues.   I’ve got 63,790 miles on the car now.   At this rate I’ll drive it forever before I do it again.  
 

There are a lot of considerations when custom ordering pistons on the form, but many of those blanks address features that wouldn’t really be necessary in a low performance flathead like our cars run. You don’t need an accumulator groove in a 7.5:1 SCR flathead and contact reduction would be of minimal value in my opinion.   I just told the rep what engine I was building and he spec’d a stock style piston (looks like a tomato can IMO...) with the thinner more modern rings.  Our decision on rings was simply made by calling Total Seal (a couple of miles from the shop) and asking what ring thicknesses they had for our chosen piston diameter.  Once we knew  what they could supply we finished the order form with ring thickness specs. The only think I believe you mentioned that you would be required to know is compression height.  That’s the distance from the center of the wrist pin to the deck of the block (where the head mates).  You don’t want your piston down in the hole robbing you of compression.  Likewise, you can’t have the piston too far above deck (also depends on head gasket thickness) where it could contact the head while the engine is running which will quickly destroy a motor. 
 

Consider discussing it with your engine machinist.  They do this regularly and can answer many of your questions as well in order to get you the proper pistons for your application.  
 

I certainly wouldn’t consider it a risky move.  It’s a pricey one, but like any other engine building process it involves care.   You can’t throw the wrong sized stock components together and expect longevity either.  
 

If I missed anything major let me know and I’ll address it.  Lunch is over and I’m heading back into the shop to continue working on my ‘67 Ford 352 rebuild.   

[Matt Wilson]

Great info, Jim!  I think I had read too many racing-oriented articles on piston and ring selection (cuz those are about the only articles out there) and I felt like I was in over my head, but it sounds like it doesn't have to be that big a deal, and that most of that stuff is not very relevant for our engines.

 

I agree that much has changed since these engines were common on the road, such as oil, so they have a much better fighting chance of long life today than back then.  I also agree that engine tune plays a significant role.  Having said that, I see folks who rebuilt their flatheads in the last 20 years or so, so they are almost certainly using good-quality oil, but they're still often getting something like 60,000 - 80,000 miles before seeing definite signs of needing an overhaul, with piston, ring and cylinder wear being a very common reason.  I'm hoping to pick/spec modern rings and improved pistons to give me a leg up in that regard. 

 

I know many folks will ask if I really plan to put that many miles on this engine, telling me to be realistic  The answer is, I don't know, but I have had this truck for over 30 years, and I plan to keep it another 30, or however long I live, so while I have it apart, if like to do a few things to improve the odds of longevity.

 

Couple more questions:

 

You mentioned you wouldn't use JE Pistons.  Do you mind elaborating on this?

 

Also, I saw that your piston-to-bore clearance was 0.0035, which seems somewhat large for a modern, street hypereutectic piston, so I'm guessing your pistons are not hypereutectic alloy (I don't think forgings are available in that kind of alloy, anyway, but I'm not sure).  With that clearance, do you ever hear any piston slap when the engine is cold?

 

Thanks again!

[thebeebe5]

1 hour ago, Matt Wilson said:

Great info, Jim!  I think I had read too many racing-oriented articles on piston and ring selection (cuz those are about the only articles out there) and I felt like I was in over my head, but it sounds like it doesn't have to be that big a deal, and that most of that stuff is not very relevant for our engines.

I was disappointed at how boring the pistons looked when I got them.  Flat tops and no “bling”.  But they’re what this engine calls for.  

 

1 hour ago, Matt Wilson said:

 

I agree that much has changed since these engines were common on the road, such as oil, so they have a much better fighting chance of long life today than back then.  I also agree that engine tune plays a significant role.  Having said that, I see folks who rebuilt their flatheads in the last 20 years or so, so they are almost certainly using good-quality oil, but they're still often getting something like 60,000 - 80,000 miles before seeing definite signs of needing an overhaul, with piston, ring and cylinder wear being a very common reason.  I'm hoping to pick/spec modern rings and improved pistons to give me a leg up in that regard. 
 

Make sure your tune is proper.  Look at the optimal air/fuel ratios for a gasoline engine in all operational ranges.  Refer to the thread if need be.  I’ve put the wide band on cars guys brought in claiming to have just “tuned” it and seen 8:1-9.1 AFR through all driving conditions.   TOO RICH, and harmful to an engine!!  
 

I know many folks will ask if I really plan to put that many miles on this engine, telling me to be realistic  The answer is, I don't know, but I have had this truck for over 30 years, and I plan to keep it another 30, or however long I live, so while I have it apart, if like to do a few things to improve the odds of longevity.

 

Couple more questions:

 

You mentioned you wouldn't use JE Pistons.  Do you mind elaborating on this?

Brian (the shop owner) has had to return too many custom orders from them.   Building a custom engine takes long enough since many “next steps” cannot be decided until current steps are finalized. Example would be grinding the crankshaft.   Until you have main and rod bearings in hand and can install, torque and measure, you can’t tell the crank grinder where you want the journals to end up. There’s possibly weeks right there to to order/receive bearings if not more (assuming they’re not shelf stock) and a month to send a crank out for grinding and return.   It can take considerably longer as well.  It doesn’t help when the piston manufacturer doesn’t make the pistons the way you ordered them. I had the same happen to me.  
 

Also, I saw that your piston-to-bore clearance was 0.0035, which seems somewhat large for a modern, street hypereutectic piston, so I'm guessing your pistons are not hypereutectic alloy (I don't think forgings are available in that kind of alloy, anyway, but I'm not sure).  With that clearance, do you ever hear any piston slap when the engine is cold?  
 

Forgings expand more than cast pistons and considerably more than hypereutectics.   Allowances need to be made for this.  Custom “forged” pistons are... forged.  I don’t appreciate “slap” at cold.  It might be there to a small degree, but it’s temporary and I don’t hear it at this point. 

 

Thanks again!

 

[Matt Wilson]

Once again, thanks!  I really value your comments.  And I will especially take your comments regarding tuning to heart.  In fact, as I re-read your thread the other day, I made a mental note that I should probably buy a device to measure the air-fuel ratio, and set up my engine like yours, so I can read that data in all driving regimes.  I can read the plugs, but using a meter seems to be the way to really make sure that things are as they should be.  It's worth it to keep from tanking my engine.  Plus, I'm a geek who likes data, so it will satisfy that part of my personality.

Edited January 23, 2022 by Matt Wilson

[Matt Wilson]

Jim, I wonder if you would mind measuring the height (thickness) of one of the head nuts on your engine?  Not sure if those are OEM nuts or if you replaced them.

 

Thanks!

[Dodgeb4ya]

The factory Dodge head nuts  on my engines  (7/16" X 20) 11/16" Hex measure at .441" in height.

They are a heavy grade automotive nut.

 

Edited February 18, 2022 by Dodgeb4ya

[Matt Wilson]

2 hours ago, Dodgeb4ya said:

The factory Dodge head nuts  on my engines  (7/16" X 20) 11/16" Hex measure at .441" in height.

They are a heavy grade automotive nut.

 

Super! Thanks so much!

[Sniper]

A note, standard nut thickness is generally the same as the diameter of the threads, a 7/16" nut is 7/16" thick.  So the measured .441" above corresponds to the math of 7/16" being .4375" calculated.

[Matt Wilson]

2 hours ago, Sniper said:

A note, standard nut thickness is generally the same as the diameter of the threads, a 7/16" nut is 7/16" thick.  So the measured .441" above corresponds to the math of 7/16" being .4375" calculated.

Ah, ok, I didn't realize that.  Thanks, Sniper.  The reason I asked is because ARP's head nuts are 0.504" tall, but I was fairly sure the factory DPCD nuts are not that tall.  As you might have figured, this is related to the head stud/head nut questions I've been asking in my other post.  I figured I'd ask this particular question of someone who I know has (or at least had) factory head nuts, hence the reason for coming to this thread.

 

[Matt Wilson]

On 10/28/2017 at 6:31 PM, thebeebe5 said:

Today's progress report:

Spent the morning adjusting my old Ford's carburetor on the wide band O2 sensor so I could get it past emissions.  That left the afternoon to wrap up the valve job.  Got all the  exhaust seats done and lapped to show about a 0.070" contact patch.  Glad they are done.  Those inserts were tough on the grinding stones.... 

 

Hi Jim,

 

Looking at the photos of your exhaust valves (and I think your intakes were similar), I'm wondering if there was any concern over the small distance from the seat OD to the valve head OD?  This photo shows only a very tiny sliver of shiny metal running along the outer circumference of the valve face, just outside the dull ring that indicates the contact band between the valve and the seat.  I've run across a few articles or sets of instructions online that indicate this sliver of shiny metal should be larger than this appears to be, for durability/longevity purposes.  One set of instructions by GM says it should be at least 0.020" wide, while others say at least 1/64" (~0.016"), while still another says it should be at least 1/32" (~0.031") wide.  But then I find forums where guys who do this type of machining for a living say they only leave 0.005 - 0.015" width, or in the case of intake valves, sometimes none at all.

 

The reason I ask is because the contact patterns on my valves (both intake and exhaust) look very much like those on yours, and they measure no more than 0.015" on the exhaust valves no more than 0.010" on the intakes) and before I install them in my engine, I want to find out if there could be any durability issues.  If so, then I might be able to order slightly larger OD valves that will work in my application (265 cid flathead six) to hedge my bets.  But I'd like to find out what your experience has been with these valves, and what the gurus at your shop say about this sort of thing.

 

I'll note that my engine will be hopped up a little, with 8:1 compression, a moderately modified cam, dual carb intake, dual exhaust, and re-curved distributor with electronic ignition.  Also, when driving at highway speeds, the engine will be at 3000 - 3200 rpm continuously.

 

I will also note that the seat widths (contact patches as seen on my valve faces) are in line with the requirements (about 1/16" or so), so at least that's a plus.

 

Anyone else who may have input on this, your advice is appreciated too.

 

Thanks!

[thebeebe5]

On 12/30/2022 at 11:37 AM, Matt Wilson said:

Hi Jim,

 

Looking at the photos of your exhaust valves (and I think your intakes were similar), I'm wondering if there was any concern over the small distance from the seat OD to the valve head OD?  This photo shows only a very tiny sliver of shiny metal running along the outer circumference of the valve face, just outside the dull ring that indicates the contact band between the valve and the seat.  I've run across a few articles or sets of instructions online that indicate this sliver of shiny metal should be larger than this appears to be, for durability/longevity purposes.  One set of instructions by GM says it should be at least 0.020" wide, while others say at least 1/64" (~0.016"), while still another says it should be at least 1/32" (~0.031") wide.  But then I find forums where guys who do this type of machining for a living say they only leave 0.005 - 0.015" width, or in the case of intake valves, sometimes none at all.

 

The reason I ask is because the contact patterns on my valves (both intake and exhaust) look very much like those on yours, and they measure no more than 0.015" on the exhaust valves no more than 0.010" on the intakes) and before I install them in my engine, I want to find out if there could be any durability issues.  If so, then I might be able to order slightly larger OD valves that will work in my application (265 cid flathead six) to hedge my bets.  But I'd like to find out what your experience has been with these valves, and what the gurus at your shop say about this sort of thing.

 

I'll note that my engine will be hopped up a little, with 8:1 compression, a moderately modified cam, dual carb intake, dual exhaust, and re-curved distributor with electronic ignition.  Also, when driving at highway speeds, the engine will be at 3000 - 3200 rpm continuously.

 

I will also note that the seat widths (contact patches as seen on my valve faces) are in line with the requirements (about 1/16" or so), so at least that's a plus.

 

Anyone else who may have input on this, your advice is appreciated too.

 

Thanks!

Matt, I apologize I did not see this when you posted.  I need to check and make sure I get emailed when a comment is added.  
 

The contact of the valve and seat is moved out to the edge of thr valve to maximize the valve size.  I could certainly seat the valve further in but I’d not be taking advantage of the full size of the valve.  With the equipment available to grind seats integral to this flathead engine block the gain is likely nil, but it’s a technique generally used for valve jobs here at the shop so I adhered to it.  It does come into play with multi angle valve jobs on motors that move a lot of air.  In some cases a proper valve job with seat contact placed to maximize valve area can see as much gains (or more!) as swapping in larger seats/valves and not taking advantage of the full size of the new valve.   Good luck with your build! 

[Matt Wilson]

5 hours ago, thebeebe5 said:

Matt, I apologize I did not see this when you posted.  I need to check and make sure I get emailed when a comment is added.  
 

The contact of the valve and seat is moved out to the edge of thr valve to maximize the valve size.  I could certainly seat the valve further in but I’d not be taking advantage of the full size of the valve.  With the equipment available to grind seats integral to this flathead engine block the gain is likely nil, but it’s a technique generally used for valve jobs here at the shop so I adhered to it.  It does come into play with multi angle valve jobs on motors that move a lot of air.  In some cases a proper valve job with seat contact placed to maximize valve area can see as much gains (or more!) as swapping in larger seats/valves and not taking advantage of the full size of the new valve.   Good luck with your build! 

Thanks, Jim!  That's interesting stuff.  Sounds like my valves and seats are just about right the way they are, in that case.

[Matt Wilson]

Hi Jim,

 

I see that you used Crower custom bushings for the connecting rods (small end) and 0.866 diameter wrist pins.  Do you know the OD of the installed bushings?  That would be the same as the ID of the rods.  I'm looking to determine the wall thickness of the bushings after they were installed and honed to fit the pins.

 

Are these bushings made completely of bronze, or are they steel-backed, as some bushings I've seen?

 

Thanks. 

[thebeebe5]

On 3/22/2024 at 8:39 PM, Matt Wilson said:

Hi Jim,

 

I see that you used Crower custom bushings for the connecting rods (small end) and 0.866 diameter wrist pins.  Do you know the OD of the installed bushings?  That would be the same as the ID of the rods.  I'm looking to determine the wall thickness of the bushings after they were installed and honed to fit the pins.

 

Are these bushings made completely of bronze, or are they steel-backed, as some bushings I've seen?

 

Thanks. 

Matt,

The bushings I did were custom.  First checked the small end for roundness and taper.  I don’t recall if I honed to correct any issues, but normally we’d hone them to make them perfectly round and eliminate taper.  Then we called Crower with a spec 0.002” larger than the rod small end ID for proper interference fit. The bushing ID is ordered smaller than the OD of the wrist pin. Once installed (press fitted) into the rod small end the bushing is honed to a final clearance about (edit for this particular build per blueprint notes) 0.0005” larger than the wrist pin for proper oil clearance.  Honestly have no idea where these ended up for thickness as that was 6-7 years ago now, but they aren’t very thick at all. Basically they just allow the rod end to be fitted to the wrist pin.   These were all bronze.  No steel shell. 
 

Hope this answers your question! 
 

JIM

Edited March 28 by thebeebe5

[Matt Wilson]

2 hours ago, thebeebe5 said:

Matt,

The bushings I did were custom.  First checked the small end for roundness and taper.  I don’t recall if I honed to correct any issues, but normally we’d hone them to make them perfectly round and eliminate taper.  Then we called Crower with a spec 0.002” larger than the rod small end ID for proper interference fit. The bushing ID is ordered smaller than the OD of the wrist pin. Once installed (press fitted) into the rod small end the bushing is honed to a final clearance about 0.0007-0.0008” larger than the wrist pin for proper oil clearance.  Honestly have no idea where these ended up for thickness as that was 6-7 years ago now, but they aren’t very thick at all. Basically they just allow the rod end to be fitted to the wrist pin.   These were all bronze.  No steel shell. 
 

Hope this answers your question! 
 

JIM

Thanks, Jim!  That's helpful.