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Joined: Mar 2010
Posts: 10,732
52Carl Offline OP
Renaissance Man
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?

Last edited by 52Carl; Thu Aug 24 2023 12:50 AM.
Joined: Oct 2021
Posts: 3,187
I think its time to find a new machine shop.

1939 Packard Standard Eight Coupe (The Phantom)
1950 Chevrolet 3100 (Ol' Roy)
1956 Cadillac Coupe de Ville (The Bismarck)
1956 Cadillac Sixty Special Fleetwood (The Godfather)
1966 Oldsmobile Toronado (The Purple Knif)
1966 Ford Mustang (Little Red)
1964 Ford Galaxie 500 coupe
1979 Ford F-100
1976 Ford F-150 (Big Red)
1995 Ford F-150 (Newt)
Joined: Jan 2019
Posts: 1,370
Herder of Cats, Goats, and Sheep (moderator)
Originally Posted by Otto Skorzeny
I think its time to find a new machine shop.


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.

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1958 Apache, long bed Fleetside, V8 w/SM420
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1959 Apache, long bed Fleetside that has been in the family for 25 years but in desperate need of love.
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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.

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Joined: Dec 2018
Posts: 2,586
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.

Last edited by fixite7; Thu Jun 01 2023 12:34 PM.
Joined: Mar 2014
Posts: 3,661
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.


1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Joined: Dec 2017
Posts: 1,328
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.

Last edited by Dragsix; Thu Jun 01 2023 03:33 PM.

Joined: Jan 2014
Posts: 3,137
Dragsix, just out of curiosity…why do you prefer the bronze liners to the bronze guides?

Joined: Jul 2014
Posts: 526
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.

1951 3800 1-ton
'62 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
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Joined: Mar 2010
Posts: 10,732
52Carl Offline OP
Renaissance Man
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.

Last edited by 52Carl; Fri Jun 02 2023 12:14 AM.
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