0.080 Overbore on 230 Flathead Six

[Matt Wilson]

Good afternoon to everyone,

I have a 230 cid flathead six in my '49 Dodge Power Wagon, and I'm looking at doing a rebuild.  The cylinders are currently at 0.060" oversize, and I'm wondering how big a deal it is to go 0.080" oversize.  It appears that Silvolite makes pistons of this oversize, based on info from their website, although I have not inquired with them to make sure they actually have them.  I intend to keep the truck for a very long time (already had it for 25+ years), and I want it to be reliable, and hence don't want to have to rebuild the engine again.  With that in mind, will it be risky to bore to 0.080" oversize?

Another thing to be aware of is that I intend to make a few performance mods to give it more oomph, such as dual-carb intake manifold, header (probably Langsdon's, as his are the only ones I know of), maybe electronic ignition, and a cam, probably from Vintage Power Wagons.  I'm not sure if that would be pushing it, in terms of reliability, when coupled with an overbore of 0.080.

I don't intend to do any high-rpm stuff, but I will at times cruise for extended periods at 3000 rpm (which will get about 60 mph with my gearing and tires), but probably never more than that.  A lot of time will spent at lower rpm's, like 1500 - 2000 rpm, when I'm offroad, in case that makes any difference.  I will make sure the rotating components are well-balanced.

I will eventually post this same question on the Power Wagon forums, but it seems that some of you guys do more of the "non-standard" type of stuff, including overboring of engines than the guys on the Power Wagon sites, so I figured I'd start here.

 

Thanks!

Matt

[Dodgeb4ya]

I have seen in the DT truck service bulletins max over bore is .060".

Heat transfer could possibly be an issue... too fast thru the cylinder wall.

I'm sure many go beyond this though and have been OK with it.

I myself wouldn't.. I follow the book.

 

Edited December 3, 2016 by Dodgeb4ya

[Don Coatney]

I suggest you have your machine shop re-builder measure your cylinders to see if an overbore is required. If an overbore is required let the machine shop recommend and or purchase the required pistons. Then the monkey is off your back.

[martybose]

When I bought a 230 to build, it was a worn out 0.060" motor.  We ultrasounded the cylinders, found they were centered with plenty of meat, so  we wound up finding a Toyota metric ringset that came out at 0.072" over, then had a custom set of Venolia forged pistons made to use them.  Bored and honed with a honing plate, been running fine ever since.

 

Marty

[Plymouthy Adams]

if your cylinder are not totally egg shaped and there is no serious score or ridge at the top of the cylinder...and taper is within limit...check the book for limits...you will find them surprising.....you can cut the light ridge, hone to seat and re-ring if your wear is within the limits...it will be a shorter life quick overhaul but for a good running engine now..it will continue to perform as ti buys you time and metal till you seriously need a rebore......

Edited December 3, 2016 by Plymouthy Adams

[DJ194950]

A friend has a 49 Ply. flathead with +.070 over with no problems. Stock type NOS pistons are still out there if your motor will clean up with that.

Sonic testing is always a good idea and most re-builders can do it now. If you are lucky and keep the same bore as Tim suggested your home free!

DJ

Edited December 4, 2016 by DJ194950

[Young Ed]

Agreed with the other guys. You need to find what you have first. If your cylinders are pretty worn it typically takes .030 to fix them. That would bring you beyond that .080 spec. 

[55 Fargo]

Check with Tim Kingsbury AoK Racing teamed up with the famous flathead guru from Pa George Asche Jr. You can certainly overbore past .060, in fact I think Mr Ache has a 230 at either .100 or .125 over.

At any rate contact Tim on this forum....

[RobertKB]

If you want to use the present engine rather than look for a replacement I am surprised no one has yet suggested having the cylinders bored to true them up and then resleeve them either to original or what your heart desires. A bit more costly but it sounds like you want to run this old girl for a while so it could be worth it. Otherwise I would look for a different engine. I recently rebuilt the engine in my '51 Dodge which had never been rebuilt and it was tired and worn and needed a 0.40 oversize bore. Personally, I would not go past 0.60.

Edited December 4, 2016 by RobertKB

[PT81Jan]

When had to bore my motor to oversize more than 0.60 my aprehencion was to get a too thin wall and as aresult a crack latest the motor is running. Decided to resleeve it, since I did not have the option to look for another one. The sleeves of course needs a bit space /larger bore diameter. At least I did not see any break throughs or slight cracks to the water jacket in this phase. Was "a bit" effort,  but with the sleeves inside I can run the engine without bad feeling in the belly. If I had the possibility (or idea...) to ultrasound the walls, this would have been my first choice.  When you know what the wallthickness is you can decide what size to bore or not... 

[dpollo]

.o80 would be farther than I would like to go not so much for the sake of cylinder wall thickness but for the very small surface that the head gasket rests on between cylinders.

[Matt Wilson]

Thanks, everyone.  I really appreciate the input.  I do intend to ask the machinist what he recommends.  I was just trying to get an idea of whether such an oversize would be feasible, and the risk associated with it.  Having said this, I have to admit that there is more to this story.  I rebuilt this engine several years ago, and have put less than 10,000 miles on it since then.  The cylinders mostly look to be in excellent condition, with cross-hatching still visible and everything...so...it seems that I could probably use as is, with perhaps a light re-honing to clean them up, especially to clean up a patch of rust I found on one of the cylinder walls.  The reason I took apart the engine is because I found some issues that need correcting, which stem back to poor work by the machine shop I hired at the time of my first rebuild.  I had a LOT of trouble with the work by that shop, and had to have a lot of it re-done.  I thought I had corrected it all, but a few years later, I found more issues that were major enough to warrant disassembly the engine and re-work.  If anyone's interested in hearing the nature of the problems, I can give you a run-down.  It's pretty sordid.  Anyway, since I now have the engine apart again, I figured I might as well make sure it is done properly, through and through, as I do not want to go through this again.  Of course, I will be taking it to a different machinist this time.

The cylinders are slightly oversized compared to OEM specs, which was at my request to the original machine shop, because I had planned on making performance mods to my engine, and I had read that it is advisable to oversize them a bit to allow for additional piston expansion caused by the added heat of the extra power.  I now wonder if that was really necessary, or if that was only meant for all-out race engines.  Anyway, if I recall correctly, the cylinders are a couple thou over normal clearances, and if I now come along and hone them, they will be even a bit more than that, which seems like not a great place to start with a freshly "rebuilt" engine.  So...I thought, hmmm....it might be interesting to entertain the idea of boring to 0.080" over, but not if it's going to be a reliability concern.

How much does it typically cost to get the cylinders x-rayed for thickness?

Also, the engine overheated severely on an early voyage, which produced a crack on the outside of the head.  The overheating was caused when a core plug installed by the machine shop fell out and allowed all of the coolant to drain out.  I didn't realize this had happened, as the temp gage did not register the increase in temperature for some time, so I kept driving.  Anyway, if the head got hot enough to crack, I have a concern that the block may have also.  After remedying the core plug issue, I did drive the truck for several thousand miles afterward, and never saw any evidence of a crack, but I still wonder.  The patch of rust I found on one of the cylinder walls seemed peculiar to me, as it was very localized to one area of that cylinder, and none of the other cylinders had any sign of rust, which makes me wonder if that rusty spot could have come from a crack.  I'll have the new machine shop perform a magaflux inspection, but I'm also thinking of bolting down a hunk of lumber onto the engine, in place of the head (or maybe I'll just install the head), and then pressurize the block with air or water to see if I find any signs of leakage through a crack anywhere, especially in that rusty cylinder.  Any thoughts on this?  I wonder if X-ray would serve as a backup to find cracks as well?

Sorry for my long e-mail, but I appreciate any help you all can offer.

Thanks!

[Matt Wilson]

43 minutes ago, dpollo said:

.o80 would be farther than I would like to go not so much for the sake of cylinder wall thickness but for the very small surface that the head gasket rests on between cylinders.

Hmmm....very interesting point that I hadn't considered.  Thanks!

[bones44]

Back in the early sixties when I was young and dumb I had a co-worker bore my replacement 230 cu“engine .080 oversize to perk it up. I than took the cylinder head to the local machine shop to have it milled .060 and discussed what was done to the block. He checked his piston books and said there were no .080 over pistons available at that time. He researched further and found if the bore was .0825 we could use .020 oversize Kaiser pistons as the wrist pin center was the same.

Long story short, assembled engine installed,drove about a week and noticed steam from breather. Pulled dipstick and found it milky, pulled pan and found coolant coming down #6 cyl.(pin hole) Removed engine an had #6 sleeved & bored. Assembled and installed. I drove car for over 35 thousand miles before parking it in 1971.

Last year I rebuilt the motor and added some Eggy modification and once again the car is back on the road.

 

[Matt Wilson]

Wow, great-looking engine, Bones!  And great story, too.  It gives me some confidence in some of my options, like sleeving the cylinders if necessary.  It also gives me a little less confidence in trying out the 0.080 over cylinders, which is fine, as it may not be a great idea.  Sleeving the block would be more expensive than boring to 0.080 and buying new pistons to go with that, but probably a lot more reliable, assuming the sleeving job is done properly.  Thanks!

[JBNeal]

With the wear and overheating issue, that block my be at the end of its serviceable life...might be time to start looking for another block and start over...what fun! 

Edited December 4, 2016 by JBNeal
added inspiration

[Dartgame]

If you end up replacing the block remember that a 230 is the same block as 218. Just different crank and rods.

[martybose]

8 hours ago, Dartgame said:

If you end up replacing the block remember that a 230 is the same block as 218. Just different crank and rods.

True, as long as you are aware of the two different setups for the thermostat housings and waterpump bypasses, and use all of the appropriate parts.

Marty

[Mick Blake]

Hi, My 1954 Canadian Plymouth 228 engine was done .090 thou over, I have never had any problems.

[Matt Wilson]

A lot of great info here, guys.  I appreciate it.  I'll be doing some more checks on my block in the next few weeks, but I'm starting to open my mind toward getting a new block.

Anyone have any suggestions on where to find these blocks locally?  I guess I could try machine shops and salvage yards.  They may have an old, rebuildable block sitting around.  Any other ideas for local sources?  I'm in the Dallas-FortWorth area.  If all else fails, I know I can get one from a variety of out-of-town places that specialize in these types of vehicles.

[JBNeal]

I know a guy south of Waco who has a 218 block that has been sitting in his garage for a few years...cuz requesting parts should only be done in the parts wanted section