Stovebolt.com Forums The Shop Area The Engine Shop Got a call from the machine shop UPDATE

1953 235 "w/Powerglide" engine. I got a call back today from the machine shop about the 848 head (originally from a '56 235). I took it there to have them look at the valves. #1 cylinder was leaking air past the exhaust valve. I removed that valve and the exhaust valve from #2 cylinder for comparison.
The contact area of the leaky #1 valve was not concentric. The contact area of the #2 exhaust valve was concentric, but the contact area where the seat contacts the valve was not centered on the bevel. It was very near the inside edge of the bevel, which is not right. It should be centered.
The guy at the machine shop says that the valve guides are worn out and need to be replaced. The guides were replaced by this machine shop 22,000 miles ago.
2,000 miles ago, this machine shop did a valve job on this head when I brought it in to have it completely overhauled due to a thrown rod.
He told me today that it needs new valve guides, and that the valves are blue from over heating. He suggested that this was from incorrect timing or from running too lean. There is an overheat indicator on the head which they put on all heads so that they can tell if operator error caused failure. That indicator was intact. The spark plugs with 2,000 miles on them look fantastic, and the top of the pistons look unfazed as well. The #1 piston had extra carbon deposits due to incomplete combustion, but it was not excessive in general.
They had put positive valve stem seals on on this head. I am wondering if those were preventing sufficient oil from lubricating the valve stems. I asked him that, but he does not think so. I have to question that, given that these engines do not spray oil all over the place like modern engines which call for positive valve stem seals do.
Would insufficient oiling of the valve stems cause excessive wear and cause the valves to turn blue from excess heat?
BTW, this engine has never gone past 180 degrees, and I never have to add coolant to the radiator, and I drive it as hard as it was designed to run.
What say you?

I think its time to find a new machine shop.

x100

If they did a valve job 2000 miles ago and the contact areas are not perfect, they done screwed it up. The fact that they are blaming you is even more sketch.

At least get a new shop, you have grounds to try and get your money back from this one but it might not be worth the effort.

X2 on the idea that you need a better machinist. I've seen premature guide wear caused by too-efficient valve stem seals, especially if positive stem seals were added to what was already there, such as the O rings in the groove under the split locks. Rather than replace the guides, try to find someone who will ream them out and install bronze guide liners. The liners are available on Ebay, and it's a fairly simple procedure to ream the guides .030" oversize and install the thinwall liners, then ream the liners to the proper oil clearance. The bronze lasts much longer than the original cast iron, especially if they're clearanced properly and used with the right design of oil seals.
Jerry

52 Carl None of my 3 OK engines has those hi-powered seals a 216,235 dipper,235 full pressure,they don,t smoke. All3 do get rid of some oil over time just my DD gets run at hiway speed a lot in the 51 6400 pickup, it has all -.002 bearings and keeps the 30 pound original dash gage pegged year round. Only one I've ever seen do that. In your case would put the head back like it came out originally,that might take valve seats,which I know are dangerous in that they can come out and kill your engine but when the seats are deep,the valve springs are weakened,then you shim. We all need a good bronze-wall machine shop !! When I done that for real was about 22 years old,the old mechanics wouldn't trust me,young racers trusted my sleeve and valve work and we had a pretty good circle track ! Ordinary domestic work I had plenty of valve,bore,hot tank,piston work. One other thing those tight seals were to keep oil out of high compression cylinders to prevent detonation,you don't have much problem there. My .02 cents On your 56 head ,not long ago I drove fresh guides in a similar head worked fine,I guess bronze walls would be the safest for your old casting there. Just saw your head was a 56 848.

I quit using those special valve stem seals 30+ years ago and I abandoned umbrella seals about 20 years ago when I discovered they were no longer made in the USA and they would crack, fall off and make a real mess (which happened in my engine). And once those umbrella seals are gone (assuming you didn't use the O ring type), you get lots of oil running down the valve stem. I've only used the flat O ring-like seals since then and have had no problems. Like Jerry said, you can over-seal them. The bronze liners should be good and if I was to re-do a head today I'd look into those, but if your valves and guides are done correctly and to OEM specs the original style should also be okay. Some people might start throwing rotten tomatoes at me but you can also have your guides knurled and that will help with lubrication of the guide. If you find somebody who knows what they're doing, this isn't a bad choice, but today finding that person may not be easy. It doesn't sound like overheating is a problem. Sorry to hear of your trouble. Not sure what to say about your machine shop.

A friend of mine built a 56 235. Had the guides replaced with new cast iron guides and PC seals. Over heated the valves and broke a guide.

I myself do not like replacing the guides. So for 46 years, I have always used bronze liners and PC seals. Not one single failure, and I run my 235 and 261 motors up to the 5500-5800 rpm range. But you have to be careful when using PC seals. They can be very efficient. That is why they entered the market. They were way better at oil control then the o-rings and umbrella seals, and they lasted way longer. There is a feel to the valves when they are just a bit too tight with the PC seals. A good machinist has that feel. If its a speck to tight, you polish the valve stems to get a tiny bit more clearance. You need a little oil, but not a lot of oil.

So frankly, if the guides themselves are not damaged beyond use, I would have them machined for bronze liners. Get some new valves, and a new machinist. Today's Serdi machines do a three angle valve job in one single cut. Get the new valves faced to match the seats, seats cut, and new PC seals with the caveat that the machinist has to check to make sure the seals are not to tight, not too loose but like Goldilocks, just right.

Dragsix, just out of curiosity…why do you prefer the bronze liners to the bronze guides?

I agree. Sounds like you need another machine shop. The fact that #1 exhaust is not concentric tells me that either the valve head wasn't ground concentric or the guide is offset. If it was wear the sloppy guide would let the valve find home and still be concentric. I've seen guides so loose that you could move the valve and spring back an forth 1/4 inch or more, yet they still sealed compression, more or less.

It's unlikely but possible that the guide was machined off center but they would have discovered that when they ground the seat. Maybe that valve was chucked off center when it was ground and they didn't check the contact on assembly. Maybe they had a bucket of small-block Chev valves and picked one that was bent and didn't check anything. I'd say there is evidence of sloppy workmanship.

I went t the machine shop yesterday to look at the head. They had removed the valves, and hot tanked so that it was bare metal clean. I could see that the area of the combustion chamber between the valves looked like it had been hit with a rose bud until cherry red and became very much blue on all six of them. I also noticed that there was no combustion chamber depression at all in the area of the intake valve.
I do not know how many times this head has been machined or if someone shaved a bunch off to increase compression ratio, prior to when this machine shop has worked on it. They have shaved it twice. Once, when they did the original total rebuild 20,000 miles ago, and a second time after I through a connecting rod 2,000-3,000 miles ago.
I am wondering if the lack of any depression in the combustion chamber near the intake valve has caused the problem of that area to cook, as well as cooking the valves.
I do have two 1954 heads (913) which I believe are unmolested and there is a significant depression near the intake valve which my '56 (848) head is lacking.
I am going to take those to the machine shop tomorrow so that he can measure the height of these to compare to the height of the '56 head to determine how much has been removed from it over the years.
I will likely just have him (not his low paid flunky) rebuild the best of the two '54 heads.
I trust this machine shop, but help is hard to find these days, let alone good help.

The 914 head can be shaved .090" to have the same compression ratio as the 848, but the intake valves must be recessed into the head the same distance to avoid valve to piston interference. Drop me a PM if you would like some more specific details on how that modification is done. It was a pretty common mod before the 848 head was available.
Jerry

I'm struggling to picture the depression Carl is talking about, and to understand how it relates head-shaving. Could someone explain or even better, post a picture?

Normally, there is a small step in the combustion chamber that slightly shrouds the intake valve. When the head is milled, unless the valve is recessed the same distance, the step goes away and exposes the edge of the valve to the flame front as the fuel burns. Obviously, the alleged "machinist" didn't know to move the valves back after the milling was done. That's another reason to find a different metal butcher!
Jerry

Gotcha. That makes sense now.

I just purchased a set of carbide-blade hand turned cutters from an Ebay seller that can be used for the recessing operation. Each one of the different size and angle cutter heads also has a set of blades on the back side that are usually used to narrow the valve seating area from the top. For instance:

www.ebay.com/itm/394349427127? [ebay.com]

Jerry

I went to the machine shop with a '54 235 head so that the height of that head could be compared to the height of the head in question.
My '56 848 head measured .050" less than than the '54 head. We don't know if the '54 head has ever been shaved, so that .050" difference may indeed be more than .050".
This has lead to an elevated compression ratio on a head which is already the highest compression ratio head available. Add to this, the lack of compression chamber volume near the intake valve, things are going to get hot and valves are going to cook.
Jethro from Virginia has graciously offered me a 848 head from his inventory.
I have dropped off the '54 213 head at the machine shop to be built, but I may take up Jethro's generous offer on his 848 head.

An untouched 848 head will be exactly 4.000" thick. In my experience the "quench trench" is approximately .070" to .080" deep. Good luck.

I would not give up on that head if, as you say it's not cracked. They usually crack between the exhaust port and the intake port up the side of the combustion chamber. I have an 848 head that's been milled a moderate amount to make sure it's flat and the quench area around the intake valve is noticeably diminished. The head is on a 261 which should give 9.2:1 + a little from milling. It runs fine on regular gas. I have a hotter than stock cam and checked the intake valve clearance to be 0.050 at minimum. I don't think your blueing is caused by high compression ratio. Probably lean mixture is the culprit. Cut the valve seats back enough to protect the intake valve and set the seat contact at the outer edge. That helps keep the edges cool. Also make sure the intake valves aren't too thin at the edges. I have cut the edges back a little to eliminate thin edges on motorcycle racing engines with no shrouding and had them survive a whole season's racing.

Measure your valve clearance with one cylinder assembled on a used head gasket. If you get 0.050 I'd say you're good to go.

Thanks Curt. That 4.000 thickness was what I needed to know, as well as the .070 to .080 quench trench dimensions.

You may well be correct about not giving up on the head, but it needs new valve guides and new valves, and who knows what all that heat did to the head. I have a couple three extra heads to choose from to put back on this engine. I would rather go that route since my out of pocket expense will be the same whether I have the current head redone or one of three others I have to choose from.

Jon G Not gonna throw anything but have to downplay guide knurling,it just wears out too soon. In the case for our old castings looks like bronze walls are the safest and very durable. However iron guides have kept these engines alive until old geezers like us could take over, right ?? So I'm not afraid to take the chance and drive in new iron guides. I pressed in a set a while back,lot better to use a big hammer and driver to fit. they're running using fresh 350 exhaust valves hard seats ,hard button on the stem in the 235 1948 splash oiler. Gonna go get ready to haul and spread white rock now !!

JW51 Where did you see bronze guides ?? I would like to have a set of those,anytime you see bronze it is usually something durable !!

It sounds like your 848 head is pretty close to being a boat anchor. Drop me a PM and I'll respond with a phone number. There's a few tricks involved in increasing the compression of the early head to make it pretty much equivalent to an 848, but it's best discussed in a 2-way conversation, not with a keyboard. That's what the hotrodders did before 848's became generally available in salvage yard
.
Anybody with a lathe and a micrometer can make his own bronze valve guides, but why bother? Thin wall bronze guide liners are cheap, plentiful, and easy to install. I'll be doing that to a 216 head in the next few days.
Jerry

My neighbor Jethro (only an hour and a half down the road), horse traded me an unmolested 848 head off of a '57 235.
It is at the machine shop now to be cleaned up and magna-fluxed, and to check the valve guides, valves, and seat conditions.

That's great. Now you can stop worrying about the truck and go relax in the Cee-ment pond!

Popped in at the machine shop today to hopefully pick up my rebuilt head. It was not done. They had not even ordered the parts yet. He printed out and handed me a quote for the job. $845.30. He said that it needs all new valves, seats, and valve guides.
My chin hit the counter and I just stared at the quote. He said, "You can take your time and think about it."
I think that he gave me a, "We don't want to work on this head price."
What say you?

I think that he doesn't want to do it. Of course the last time I had valve work done was on my Model A when I was in college. I drove to the machine shop, removed the head, watched while he repaired the seats and replaced the valves (I had bought some cheapo offshore ones that burnt out in short order), paid him maybe $50, replaced the head and drove back to my dorm. So I really don't know what the going rate is.

Yep, my chin hit my desktop and I agree with you. This is the same shop that worked on it before? Kind of lost for words, there. Didn't Jerry say he had a head?

Sound a bit steep to me. Definitely an “I don’t want to work on your head price”.

"$845.30. He said that it needs all new valves, seats, and valve guides."

Carl,

Does that include prepping/machining and reassembly of the head?

What are your options?

Yes. It will be ready to bolt on to the block when they are done. That is how all machine shops I have dealt with do it.
One option is to find another machine shop and go back to this one and say no thanks and take my head back.

They already screwed it up once.

They clearly don't want to do it now.

If someone doesn't want to do something, paying more for it it isn't going to insure that it's done with the care it deserves.

Grab that head and RUN- - - -do not walk away! I just rebuilt a stovebolt head with all new valves, springs, and positive seals for a parts cost of slightly less that $100.00. I even used stainless steel exhaust valves- - - -they're the same ones that fit a small block V8. Are you up for a road trip to Tennessee, or shipping the head to me? PM or give me a phone call.

For instance:
https://www.ebay.com/itm/193918558086?

Jerry

Sounds like and appt and road trip to HRL. Yep, I'd check around. If i had one I'd give it to you!

1500 mile round trip from Carl's to Jerry's. That's 250 bucks in gas and a motel room.

Blue Line Freight (Fastenal)- - - - -burn their Diesel fuel instead of your gasoline.
Jerry

Yes. It will be ready to bolt on to the block when they are done. That is how all machine shops I have dealt with do it.
One option is to find another machine shop and go back to this one and say no thanks and take my head back.

I am going to pick up the head on Monday, and try to find another machine shop.

Update.
Got Jethro's head back from the new to me machine shop. I horse traded him a razor sharp Case folding knife, and a 3 speed transmission for the 848. He threw in a spitload of sweet corn and a head of cabbage. We surely both walked away thinking that we made out like bandits.
The machine dhop did the following:
All new intake valves, and new stainless steel exhaust valves.
New valve guides, and new valve seats. (the old seats were hammered too deep to retain the proper geometry of the rocker arms.
They shaved just the bare minimum from the head to make it true.
They milled the side of the head where the manifold goes.
He charged me $400.00 for rebuilding a head which literally needed everything. That is less than half of what my now former machine shop wanted to charge me.
I just got done priming it, and am fixin to paint it dark gray.
Tomorrow it is going back on the engine.

Sounds like you have a busy day tomorrow. I bet your excited to install the head and get her running again. I know I would be. Good luck!

The cabbage was clincher.

Carl's former cylinder head is now a resident of my shop, where it's going to get a full rehab, including oversized intake and exhaust valves and some minor port reshaping. It's going to find a new home on a highly modified 261 I have on the drawing board. Putting 1.94 inch intake valves for a Powerglide-equipped spray oiler 235, and 1.6 inch diameter stainless steel exhaust valves for a small block Chevy V8 puts the valve seating area out into a fresh area of the cylinder head where valves have never been seated before. It takes a lot of metal butchery that the average machine shot can't (or more accurately WON'T do), but the results can be pretty impressive on the dyno. Thanks again, Carl, for donating that head to the cause!
Jerry

Donating?! I skinned you alive on that horse trade. A chicken sandwich, and you let me supersize the drink and fries.

Got Sweet Pea all back together. She wouldn't start. No spark.
Had voltage at the voltage reducer, fore and aft.
Had voltage at the coil at the "+" and "-" lugs.
Had voltage at the distributor.
Had voltage at the points.
No spark when manually opening the points. BINGO.

Burnished the points with a business card and got spark while opening the points.
Put the cap back on and she started right up.
Brand new everything on that 848 head. Valve seats, stainless steel exhaust valves, new intake valves, new valve guides.
This engine has never run smoother.
A plan has come together, finally.
The best advice which was offered on this thread was, "Find another machine shop." I did. Thank you all.

That's excellent. And you're welcome.

" I love it when a plan comes together!" Enjoy the ride!
Jerry

Great news! Thanks for the wrap up!

Moral of the story.
Make sure that your machine shop knows their stuff about these old engines, or are able and willing to do the research.
In order for you to determine if THEY know their stuff about these engines, YOU need to know your stuff so that you can ask the right questions.
I did not ask the right questions and it cost me $1800 for a second rebuild caused by a broken connecting rod, likely caused by too much compression from the machine shop not knowing what the specs are on the head thickness of a 235.
The second rebuild lasted 3,000 miles before the valves were cooked by overheating in the combustion chamber from too much compression and absence of a quench trench. I am lucky that I did not break another connecting rod before I pulled the head looking for why I had a bad miss on the #1 cylinder.

I will be truthful, I agree that the first shop totally and completely messed up the head. But I think there was more to it then just a little extra compression. I think they really did not know what they were doing over all and all of it contributed to the failures. Really happy to hear you have it all sorted out and running well!

Once I get the new oversize valves fitted (properly) to the problem head, it's going to be interesting to do a CC test on it and calculate the static compression ratio when it's combined with a "261" engine that's actually going to approach 300 cubic inches. The "more is better" approach to compression is sort of a myth, since a lot of people don't understand WHY compression is increased on a high performance engine. When a radical camshaft is installed into an engine, it gets that extra power (only at high speed) by keeping the valves open longer- - - - -opening earlier, and closing later. In the case of the intake valve, that means that a good portion of the compression stroke happens before the valve closes. It's impossible to build up compression pressure in a cylinder with a valve open- - -even slightly. So- - - -if you want to get the compression pressure back up to where it was on a stock engine- - - -you've got to squeeze what's left of the cylinder harder. That requires a dome on the piston, and/or a smaller combustion chamber- - - - -JUST TO GET BACK TO SQUARE ONE!

Increasing the compression ratio without installing a radical cam approaches a situation where spark plugs aren't required- - - -better known as a Diesel engine! Most gasoline engines aren't built to survive that kind of abuse!
Jerry

During a "normal" engine rebuild where the cylinders are bored over .0030 or .0060 due to normal wear and tear, how does this affect performance since the factory camshaft is usually installed.

A Chevy 350 bored .030" oversize goes to 355 cubic inches. That's 5/8 of a cubic inch per cylinder increase in volume. For all practical purposes, the increase in compression can be ignored. There needs to be a big increase in bore and/or stroke, or a dramatic reduction in combustion chamber size to make a big difference in compression pressure. That same 350 with a 76CC cylinder head has about 8.5:1 compression. A 64 CC head brings it up to around 9.5:1 or maybe 10:1. Domed pistons and a 64CC head approach 11:1.

A Chevy 230 six has flat top pistons. A 250 has a 1/4" dish in the piston top and uses the same cylinder head. That's a difference of slightly under 4 cubic inches per cylinder, from a longer stroke on the 250. The dished piston is there to keep the compression the same on both engines. Running a flat top piston for a Chevy 307 V8 in a 250 brings the compression up to about 9:1.
Jerry

Thanks.

My engine was bored .060" over, and there is .050 missing from the bottom of the head, leaving most of the quench trench by the intake valves missing. The machine shop also put in all new valve seats at an unknown level. If the new seats were ground too shallow, compression would be even higher.
I did a hot compression check on all cylinders before I pulled the head, #2 through #6 were at 240 PSI (+/- 5 PSI), and the #1 with the leaky exhaust valve was at 180 PSI.
That is about 100 PSI too high. Its a brand new gauge. I doubt that the gauge is off by 58%.

When I do some major metal butchery on that head- - - -bigger intake and exhaust valves, recessing the intake valves back to the proper depth, opening up the combustion chamber around the bigger exhaust valves to unshroud them, and a few other kinds of metal butchery- - - -I'll have one of two things- - - -a really good-performing head that can be paired up with a pretty radical cam, or a boat anchor! I won't really know until I'm about 75% of the way through the job. If I end up making the head worse than it already is- - - -no big loss, as I can use the new valves in a different head if that one can't be salvaged. I've got a few other sneaky tricks up my sleeve for the engine, other than the cylinder head mods I've mentioned.
Jerry

Yep. You are only into this for a delicious chicken sandwich, large fries, and a large Diet Pepsi.
I still say I came out ahead way ahead on that horse trade. I literally "ate your lunch."

LOL! If you've got another head handy, there's a second course waiting. There's a really good BBQ place a few miles south!
Jerry

There's a gutton born every day.

Locking this thread! Story has gone full circle.