deadeyejedi

can anyone tell if this is an original piston for a 1970 olds 350 ? any reason why this valve started leaking? Ive been working on this motor for a while and tracked the low 90lbs of compression in the number 7 cylinder to a exhaust valve leaking by. all the other cylinders have about 150lbs of compression.the pics are what ive got so far.is it time to send this head to a machine shop and have it checked out?

66SportCoupe

Pistons look to be original high compression cast. The valve might be able to be fixed just lapping it. Otherwise have the heads freshened up.

deadeyejedi

most of what im seeing this motor looks more like a stock refresh.The cam lifters and pushrods appear to be newer and i would guess it had a rering and hone.more than likely started out at 10:1 compression ? seeing the felpro head gasket ill assume the cr is a bit lower now .i might spend the time and money to cc these heads and do some measuring to get a more accurate idea of what i have.thank you for your reply

deadeyejedi

Another question . On average how far in the hole did these factory pistons sit? Would like to measure and compare my results to see if this block were decked.

RetroRanger

Did you remove the valves and inspect the mating surfaces?

Dynoking

Remove the suspect valve from the head. Post clear pictures of the valve and the seat. What makes you think this valve is bad?

deadeyejedi

I have not removed the valve yet I ran out of time last night . It should be clear what’s going on once I get it out . It’s either the valve or seat because I had shop air hooked to it and it was blowing out the exhaust . Last night I filled that chamber with solvent and it leak right past the valve .

deadeyejedi

Not sure about this valve and seat but the guide is almost egg shaped with a lot of play between it and the valve stem.

66SportCoupe

With seeing that I would have heads refurbished and put it back together.

deadeyejedi

I spoke with my machine shop and he gave me a ball park of 600 to have a valve job and all new seats I guess I have to make a decision now .

Sugar Bear

The guide should be addressed and although unlikely the valve spring could be weak contributing to low compression. Probably best to completely disassemble the head and do an inspection.

Sugar Bear

All new seats may not be necessary.

deadeyejedi

Maybe not but I’m usually not that lucky😂

OLDSter Ralph

Plan on valve guide work on all guides, a couple seats, a couple valves, and maybe a good .020" removed from the head deck surface.

deadeyejedi

Sorry I just reread this I meant to say all new valve guides not seats

Sugar Bear

Consider getting recommendations for valve guide seals from members that have had success and then discussing it with the machine shop vs. using whichever the machine shop has available.

Good luck!!!

BillK

Do you have any idea how much .020" is off a cylinder head ?????? There is nothing I see that shows that the gasket was not sealed up other than one small spot. I bet that .005" will clean it up.

To the OP, that one guide is definitely worn out and if so most likely all of them will be the same. It may or may not need seats. No way to tell just by looking. The head has been off before and might have even had a valve job done on it then. Only way to know exactly what it needs is to start measuring things. $600 is cheap if it if it needs all of the guides and resurfacing.

That being said, it almost looks like the head has been welded up before ??? The pitted area I have circled does not look like normal corrosion. Has your machine shop actually looked at the head ??

Sugar Bear

Bill good catch on the possibly welded area. Do you have any valve seal recommendations?

deadeyejedi

Bill , I’m planning on dropping the head off next week to the machine shop . I will inspect the area circled further . I didn’t even give that spot a thought til you mentioned it .I was told these heads were redone at one point but have no idea to what extent . I really didn’t plan on spending much money on this motor well see what the machinist says.

deadeyejedi

after cleaning this up a bit it looks good i see no evidence of welding .the more i think of it these heads probably got a clean up and valve job. im going to try and cc it and see where thats at. is it possible to just put one guide in this and fix the one valve??

Sugar Bear

Yes it is possible to fix one valve and one guide; but, I wouldn't do that without eyeballing everything else as there maybe/likely others on the edge of failing. It's a personal choice which depends on your budget and long term goal.

Good luck!!!

66SportCoupe

x2

67OAI

In the picture of the valve seat in post #8, it appears to me that an improperly dressed or clogged stone was used and caused a radial scratch that has collected carbon buildup. It should clean up okay with a fresh touch up after any necessary guide work has been done. Your machinest will have the proper instruments to measure the valve stems and valve guides to determine exactly what work shall be required. It is hard to tell in the pictures you have posted whether the deck surface of the block or the surface of the head has been previously surfaced. The factory finish leaves faint machining lines that are in a straight line fore to aft like planing; most machine shops use equipment that leave faint machining lines that are across the surface and slightly curved from a milling machine type of cutter. The blue color tells me that Felpro composite gaskets were used last time heads were off. The composite gaskets are about .042" compressed and the original factory shim steel gasket is about .017" compressed so if you have about .025 or .030" removed from the head surface you should be back close to factory specs with the composite head gasket. Oldsmobile originally used rubber type umbrella valve seals which always deteriorate and fall apart over time. Sometime later they started using a nylon plastic type of material which holds up much better. I favor those for use on a street motor over the positive type of valve seal.

deadeyejedi

i dont really see any indication of previous milling on the block or the the heads. i have a set of felpros on the shelf so probably will use them when i put it back together i should be around the 9:1comp range which is fine with me .i wish i could find videos of the the valve guide process for an olds head. The way i see it you either have to drill the guide out bigger and use an oversize stem(haven't seen them available) or drill out the guide and insert a sleeve of some type.The way its worn i think its too late to simply knurl it .ill go over all this with the machine shop this week .

67OAI

I don't know if anybody still tries to use the knurl process on a valve guide repair. If anything, it is a short term repair, a bandaid. Most Oldsmobile heads I have seen have knurled valve guides from the factory but that is for better oil retention. When replaced, the insert probably won't have knurling. If having all the guides replaced, I would have bronze guides installed, just my preference.

OLDSter Ralph

x 2

Dynoking

x3!

deadeyejedi

This block doesn’t appear to ever been machined .as it sits with factory pistons and no deck work these pistons sit an average of .029 in the hole this will help me to figure out my compression ratio. I’ve measured a bunch of the valve stem clearances and they all seem to be within spec of my manual with the exception of the one exhaust valve. I did notice one new valve stem guide . I’ll have the machinist measure as well and go from there . They are original 1970 #6 heads so I’d like to get them up to par and use them.

Sugar Bear

The visible letters "C" for bore size/factory piston fitment indicate the block has not been decked.

deadeyejedi

ive been playing around a bit trying to cc my number 6 heads . the factory tells us they are 64 cc mine measure out to about 66 which isn't too far off. i tried it with a set of my core number sixes and came out about 65.5ccs.i think ive read that the high compression 70 350 was around 10.25 :1 which would be off using exact numbers.I know a lot of this has been said before but when my memory starts to go i can refer back to this thread

olds 307 and 403

You will be no where close to 10.25 to 1 with a .042" thick Felpro head gasket and the factory 6cc dish pistons. 029" in the hole. I get a hair over 9 to 1 with a 66cc head. Rebuilt with a clean up mill will push you closer to mid 9's. It still allows a decent cam upgrade. Here is a good calculator.
https://uempistons.com/p-27-compress...tio-calculator

deadeyejedi

i know i won't be close to 10-25 :1 my point there was neither was the advertised compression ratio for the stock unit . my hope is to clean up the heads fix any valve stem guide issues and put it back together.i have no idea what cam was installed in this motor at the refresh but im just gonna go with. I have 0 plans for this motor so far only to stand around it with my buddies drink beer and rev it up on the run stand

olds 307 and 403

Nothing wrong with that. Looks like it already had Felpro blue head gaskets. With 150 psi, regular gas will be no issue.

deadeyejedi

can I actually get anything thinner as far as head gaskets without paying an arm and a leg ? I’m not seeing a whole lot of choices other than the cometics .

66SportCoupe

The .027 Cometics are the thinnest now unless you find NOS GM.

tkcutlass

If I recall correctly there is a rv cam in there. rebuilt around 1990 or so. https://www.summitracing.com/parts/mel-cl-mto-1 or similar is my guess
Should be only around 5k on the rebuild.
It had an exhaust leak, is it possible the exhaust leak caused problems with that valve guide?

olds 307 and 403

I think Mr Gasket are .038". If it has the 204/214 Melling cam, low 9 to 1 will be perfect.

deadeyejedi

thanks Tim , good info to figure this thing out . There is evidence of at least a few guide replacements maybe the shop back then opted not to do the ones that met tolerances. I could only guess . Everything else seems to spec out pretty good .at some point I’ll get it back running and post a video.

deadeyejedi

https://www.speedwaymotors.com/Mr-Ga...5-,288499.html We’ll within my budget 👍

deadeyejedi

Cue the snowball effect! Well to hell with it i brought the heads to the machine shop to have them fixed up. I decided to start cleaning and painting some of the parts .The internals of this engine are in pretty good shape.I did find a replacement piston in the number 2 hole but it specs out the same as the rest.