bad exhaust valve
#1
bad exhaust valve
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?
#3
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
#7
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 .
#17
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 ??
#19
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.
#20
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??
#21
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!!!
Good luck!!!
#22
#23
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.
#24
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 .
#25
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.
#26
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.
#27
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.
#28
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.
#30
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
#31
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
https://uempistons.com/p-27-compress...tio-calculator
#32
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
#34
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 .
#36
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?
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?
#37
#38
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?
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?
#39
https://www.speedwaymotors.com/Mr-Ga...5-,288499.html We’ll within my budget 👍
#40
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.