Valve guide - cut off and blend tops?

[Bryan]

So, I found I could buy a $12 air hammer from HF and go to my brother's air compressor and drive the valve guides out sometimes next week when it warms up.   I know the ID is .344-.345" (11/32").   Does anybody know the OD of the guides?   Any brand driver needs to be slightly smaller than the OD and of good steel. Just want to order the tool and not waste next week.

Edited January 29, 2022 by Bryan

[Matt Wilson]

Napa part numbers VG419 and VG420 are the guides, and Napa's website says their OD is 16.695 mm, which converts to 0.6573" for both part numbers.  I have several used ones that came from the 251 that I'm coverting to a 265, and those measured between 0.6568 and 0.6570.

Edited January 30, 2022 by Matt Wilson

[Matt Wilson]

I ordered the valve guide driver in the photo below, many years ago, to drive out the guides in my 230 flathead six.  Ordered it from Goodson, as you can see (part number GP-524-G).  It worked just fine when used with a big freakin' hammer.  I seem to recall having to smack it pretty hard, but it wasn't a big deal.  I had my engine on a stand that supported it only at the back, and I was concerned about hammering so hard with the front of the engine unsupported, so I grabbed a 4x4 or 6x6 piece of wood that I had laying around and used that to prop the front end up.  Worked well and I don't think it was expensive - something like $10 around 10 years ago.

Edited January 30, 2022 by Matt Wilson

[greg g]

Put the guides in the freezer before installing them.  I sprayed down the holes with pb blaster before putting the guides in.  Leave them in the freezer till you are ready to put them in.  I suppose you could also warm the block with a torch also. 

[Bryan]

Took a few pics of the ports while messing with tappets.   I've read from various sources that on flatheads people cut the top of the valve guide off and blend it in with the port .  Tempting..

[Bryan]

I'm wondering if anybody has cut off the tops of their valve guides and blended them to the port base for better flow?  I have seen several posts from Flathead Ford sites about doing this.   Makes sense but wondering how it would affect reliability?  Designers must have seen this and installed high valve guides anyway. The motion is up and down with little or no side forces.   Heat absorption maybe to protect the exhaust valves from hot gases?  But then why the intake guides sticking into the ports?    Looking at mine and all the carbon and crud, trying to elevate the top of the guide above that?   Needing a specific length for travel?    Seems like shortening/blending would really help flow but hesitant to do it.  

[sidevalvepete]

Did the Chrysler engineers do this in any of the later blocks? This engine was manufactured and refined over some decades. If the later ones don't have this adaptation then there's your answer. Either detrimental or offers no benefits. Just my thoughts anyway....

[Merle Coggins]

If this were a high RPM, high performance, engine it may make a difference. But I wouldn't expect you to gain enough performance differences to warrant the added work, compromising the integrity of the valve guides in the process. 

[Dartgame]

I'd think if you reduce the length of the guide you are promoting faster wear on the remaining portion in the block. I'd have to measure how much is being removed to judge whether it is worth it. 

Edited February 3, 2022 by Dartgame

[kencombs]

I considered the same on my 230.  I was concerned about shortening it causing excessive guide wear.    Decided discretion was the better par of valor.  Sp I settled for gasket matching the block and manifold an a slight cleanup and tapering the upper end of the guides.  Might no help at all, but it was fun.

[Sniper]

I don't think guide length is an issue, there is no sideloading on the valve like it would have in an OHV setup.  I also think taking the guide out of the port is probably the most substantial thing you could do to improve port flow.  Better than a cam or port matching. 

[Bryan]

25 minutes ago, Sniper said:

I don't think guide length is an issue, there is no sideloading on the valve like it would have in an OHV setup.  I also think taking the guide out of the port is probably the most substantial thing you could do to improve port flow.  Better than a cam or port matching. 

Do you think heat transfer to the block is a reason?  Same thing with the exhaust guides being turned one way, the intake the opposite. I'd love to whack them, just I'm wanting it to be reliable instead of high rpm.   If there was no reduction in reliability, I'd do it.  Just don't know why the engineers didn't change it

[Sniper]

You have to remember that the flat head was designed in the early 30's.  Back when a lot of engineering was more guess than science and probably not revisited as it was sufficient unto the day.  Anyway, the only formula I could find is in this thread

 

https://www.speed-talk.com/forum/viewtopic.php?t=19767

 

Which works out to a guide length of 1.89" for out flatheads.  That's about an inch shorter than stock.  Remember his math is also based on the fact that he's working with an OHV setup that also imparts a side force on the valve as the rocker tip wipes across it.  Something we do not have to deal with.

 

How does this sort out with more modern designs?  Looking at a 1990 318, last year of the LA318, we see a stock guide length of 2.625" and a calculated length of 2.13", closer but still longer.

 

If you look at any porting instructions I cannot recall any of them leaving the guide protruding into the port much beyond the amount of the head casting protrusion and all of those have much smaller diameter guides, not that tree setup we have.

 

Here's an interesting thread on porting the Ford flat head with a discussion on guide shortening.

[allbizz49]

I personally don't think the juice is worth the squeeze on this one. I'd say maybe if you had a full tilt build that you were trying to get everything you could from the motor. Plus, what about the valve stem? Isn't it still obstructing flow? Of course, not as much but it's still right in the path. 

[FarmerJon]

2 hours ago, Sniper said:

I don't think guide length is an issue, there is no sideloading on the valve like it would have in an OHV setup.  I also think taking the guide out of the port is probably the most substantial thing you could do to improve port flow.  Better than a cam or port matching. 

I think it is also one of the easiest ways to improve flow.

Bryan is installing new guides anyway. Figure up the length, cut them, debur them, install them. 

 

If you feel flush with port floor is too short, you could also turn them thinner where they are in the port, and round the tip into a 'bullet'. 

Check out the math, but I would go flush to the floor, or just above it. 

 

[Bryan]

28 minutes ago, FarmerJon said:

IIf you feel flush with port floor is too short, you could also turn them thinner where they are in the port, and round the tip into a 'bullet'. 

Check out the math, but I would go flush to the floor, or just above it. 

 

I thought about that also, rounding the tip, but was wondering how they could be pressed or driven in without damaging the tip.   I'm still wondering if the guide is also some type of heat sink that absorbs heat that's transferred to the block.  Going to look that up.

[Bryan]

This is for modern engines with valves in heads, but look at 5th paragraph.  Worn Valve Guide Repairs - Engine Builder Magazine.     Heat transfer through valve guides - High Power Media    Valve guides, guide fits, and why it matters: A general overview - AMCA Forum (antiquemotorcycle.org)     https://forum.hetclub.org/discussion/172582/hudson-212-engine-valve-guide-modification

Edited February 4, 2022 by Bryan

[Sniper]

Everything is a balancing act.  Don't forget that the modern engines being talked about in your sources also spin at higher rpms.  Which means more heat.

[kencombs]

One of the reasons I chose not to do this, as mentioned in my earlier response is the higher rpm Sniper highlights.

2 hours ago, Sniper said:

Everything is a balancing act.  Don't forget that the modern engines being talked about in your sources also spin at higher rpms.  Which means more heat.

The higher rpm results in higher velocity, and volume,  air flow thru the intake and exhaust systems.  Absent that increased flow I was unsure of the gain possible, especially since I did no  oiling system mods and will never exceed 4k rpm with the flathead.  Well I am adding a full flow filter but no changes in flow, bearings or pressure.

[1936Forepoint]

I've done it on mine.  Tony Smith has been doing this for some time on his flathead rebuilds.  As Sniper said, there are no side loads on these valves.  Spot facing the guide down to closer to the port surface opens up the port considerably.  As far as heat transfer, it seems to me that there would be less heat delivered to the valve stem since the guide is not sticking out into the exhaust flow.  Less opportunity for heating the bearing surfaces of the guide.  Combining this with port matching gives a much smoother passage for intake and exhaust gases. 

[Bryan]

3 hours ago, 1936Forepoint said:

I've done it on mine.  Tony Smith has been doing this for some time on his flathead rebuilds.  As Sniper said, there are no side loads on these valves.  Spot facing the guide down to closer to the port surface opens up the port considerably.  As far as heat transfer, it seems to me that there would be less heat delivered to the valve stem since the guide is not sticking out into the exhaust flow.  Less opportunity for heating the bearing surfaces of the guide.  Combining this with port matching gives a much smoother passage for intake and exhaust gases. 

That someone has been doing this for a while is a plus.   I disagree about the stem statement. The guide sticking into the exhaust flow would absorb heat and pull it to the block. The exposed valve stem would absorb more heat if exposed, question being (as some of the posts in the links stated) is the percentage shortening change in the 25% of heat the guide absorbs enough to worry about?

[FarmerJon]

The intake ports would be my main focus, since they are siamesed. 

My shop manual stated intake ports are 1.25" diameter. 

How do the guides look in the exhaust side?

 

Good flow should help all RPM range, and reduce fuel drop out.

There are some plans floating around for a shop vac based flow bench....

 

 

[1936Forepoint]

4 hours ago, Bryan said:

That someone has been doing this for a while is a plus.   I disagree about the stem statement. The guide sticking into the exhaust flow would absorb heat and pull it to the block. The exposed valve stem would absorb more heat if exposed, question being (as some of the posts in the links stated) is the percentage shortening change in the 25% of heat the guide absorbs enough to worry about?

Bryan, You may be correct but I'm not so certain and I'm not sure that anyone can be certain.  There are a lot of things at play here and outside of a lab, an engine dynamometer and some very accurate test equipment it may not be possible to know for sure.  It sound like we agree that the majority of heat transfer 70-85% on exhaust valves happens at the seat.  This leaves 15-30% to be transferred to the guide.  The majority of that happens in the cooler end of the guide.  I suppose that my argument on heat transfer is more theoretical than anything but it appears to me that the surface area of the guide that protrudes into the exhaust gas stream acts as a heat collector and that surface area is something on the order of four times the surface area that is presented by the valve stem.  My theory, and it's only a theory, is that less heat is collected by the valve stem in the exhaust stream than what would have been collected by the much larger valve guide in that stream.  The portion of the guide that is in contact with the surrounding cast iron block is where the more significant heat transfer takes place and that valve guide is now much much cooler than it would otherwise have been.  I also believe that it's mostly an academic discussion anyway as our engines are relatively slow turning, low power output engines that are not needing to dissipate as much heat anyway.  at around 1/2 hp per cubic inch, the temperature and physical stresses are quite low compared to most more modern OHV engines.  For those of us trying to eke out as much HP as we reasonably can from our little flatheads, these little bits can add up.  I just got my 23" Dodge 230 running after re-build so I can't claim much at this point.  I'm hoping for around 150-160hp at the rear wheels.  Materials science has come a long way since most of these engines were built.  My valves are new production chevy valves that have much better materials properties than original. Bottom line, In my opinion, I don't see any real downside to shortening the guides in these engines. If your engine is mostly stock in all other areas, I doubt that shortening the guides will provide much additional flow.  If on the other hand, you're attempting to achieve better flow through improved cam, intake manifold, exhaust manifold(s), the removal of the protruding guide from that flow is a significant obstacle to achieving your best possible flow through the engine.  If your opinion differs, another option is to reduce the diameter of that portion of the guide that is in the flow.  This would leave the same valve to guide contact area intact while removing some of that impediment to flow and also the amount of surface area that is collecting heat from the exhaust gasses.   

[Bryan]

10 minutes ago, 1936Forepoint said:

Bryan, You may be correct but I'm not so certain and I'm not sure that anyone can be certain. .....   My theory, and it's only a theory, is that less heat is collected by the valve stem in the exhaust stream than what would have been collected by the much larger valve guide in that stream.  ........If your opinion differs, another option is to reduce the diameter of that portion of the guide that is in the flow.  This would leave the same valve to guide contact area intact while removing some of that impediment to flow and also the amount of surface area that is collecting heat from the exhaust gasses.   

Understand that...and that's a good point..a slim shiny valve stem might absorb less heat exposed than a large rough guide surface.  I'll definitely change something.  And I'm not sure of anything with this.. was hoping there were some folks that had done this a while back and had some data on reliability.   I have a dual exhaust header to put on it after breaking the original taking it off. In a few years I'll add dual or triple carbs. Just wanted to get it overhauled and running. But grinding guides is something I would not want to do 2 years later on a new engine. Prop the valves up, slide an improved cam in later, but no grinding.

[Matt Wilson]

Just one piece of data here, for whatever it's worth.  One factor in my decision to pull the 230 out of my Power Wagon (though a small factor compared to the metal shavings I discovered coming from the tappet bores, which I discussed on your other thread) was that the valve guides were worn.  I had paid the machine shop to replace all guides, but I'm 99% certain they didn't, since I later found that there was 2 - 4 times the allowed valve-to-guide clearance per the manual in most or all of them.  I had somehow overlooked this when assembling the engine.  The valves were new, so I knew it was an issue with the guides.  I'm pretty certain I've also read about other people with guide wear on these engines.  My guides were completely unmodified, just FYI.

 

The point of this is that guides in these engines do wear, despite there being no side loads and despite the low-rpm operation, etc., so cutting down the length may accelerate that.

 

Having said all this, my engine ran well when I decided to pull it, but who knows how long it would have stayed that way.  Cutting the guides may produce other issues, such as allowing oil to get sucked into the combustion chambers more easily.  My combustion chambers were somewhat of an oily mess, so some of that may have been taking place.

 

Though it's not 100% solid data for your decision, I think it's worth considering.