40 V8 compression change all cylinders same time

L78CHEVELLE said:
Got the leak tester and hooked it up to each cylinder at top dead center. I put 100 psi into each cylinder and got the following results:
#1 cylinder held 90 psi
#2 cylinder held 65 psi
#3 cylinder held 60 psi
#4 cylinder held 65 psi
#5 cylinder held 75 psi
#6 cylinder held 90 psi
#7 cylinder held 75 psi
#8 cylinder held 75 psi
Each cylinder tested lost the air pressure through the intake valve with air coming out of the block in the intake valve opening.

Today I took both heads off the engine and took all the valves out of the block. Here is what I see: #2 cylinder intake valve guide was stuck in the block when I tried to take it out. Surface sealing of the #2 intake valve against the seat was not uniform around the intake valve rim. Same deal on cylinder 3, 4, 7, and 8. Intake valve guides were stuck in the block, and surface sealing of the intake valve against the seat was not uniform around the intake valve rim. The exhaust valve guides were not stuck and the exhaust valve rims look like they were making an acceptable seal with the exhaust valve seat. I am going to clean up the valve seats and go with new stainless steel valves, new one piece guides, and new Mercury heavy duty valve springs. Looks to me like all this trouble and time lost is nothing more than a bad valve job on a low mileage rebuilt engine with less than 2000 miles since the rebuild. Odd the intake valves are the problem to me, and the compression decreased so quickly and uniformly on 6 of the 8 cylinders. What do you think?
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L78CHEVELLE said:
Today I took both heads off the engine and took all the valves out of the block. Here is what I see: #2 cylinder intake valve guide was stuck in the block when I tried to take it out. Surface sealing of the #2 intake valve against the seat was not uniform around the intake valve rim. Same deal on cylinder 3, 4, 7, and 8. Intake valve guides were stuck in the block, and surface sealing of the intake valve against the seat was not uniform around the intake valve rim. The exhaust valve guides were not stuck and the exhaust valve rims look like they were making an acceptable seal with the exhaust valve seat. I am going to clean up the valve seats and go with new stainless steel valves, new one piece guides, and new Mercury heavy duty valve springs. Looks to me like all this trouble and time lost is nothing more than a bad valve job on a low mileage rebuilt engine with less than 2000 miles since the rebuild. Odd the intake valves are the problem to me, and the compression decreased so quickly and uniformly on 6 of the 8 cylinders. What do you think?
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I'd assume the stuck intake guides had seals on them, the exhausts did not? A pretty common situation.

It sounds like you're lucky 2 of the cylinders had compression, it does sound like a bad valve job.
 
Russ/40 said:
Did you perform the test I suggested in my post #80?
What was the valve to guide fit like?
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Russ, I did check the guide and valve on the worst cylinders and they show no play. All seem normal. Like you suggested I have gotten the 2000 mile rebuilt engine thinking out of my mind and am treating this as a valve job. I will be using a stone on the valve seats to clean them up and installing all new valve train components except the lifters. I will post my results and findings for all that have an interest.
 
Ross F-1 said:
I'd assume the stuck intake guides had seals on them, the exhausts did not? A pretty common situation.

It sounds like you're lucky 2 of the cylinders had compression, it does sound like a bad valve job.
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The intake and exhaust valve guides both had rubber seals on them. No exhaust valve guides were stuck in the engine.
 
when you get your new valves, just for confirmation, drop the new valve in, and check with the blue stuff to see where your contact area's are, and maybe get away with just lapping since its pretty new. long chance, but the reason i say this is you mention using a stone to do seats. in the car, a much cleaner method would be the new way seat cutters. easier mess to clean up, no stone grit flying around in your new motor. best wishes
 
cas3 said:
when you get your new valves, just for confirmation, drop the new valve in, and check with the blue stuff to see where your contact area's are, and maybe get away with just lapping since its pretty new. long chance, but the reason i say this is you mention using a stone to do seats. in the car, a much cleaner method would be the new way seat cutters. easier mess to clean up, no stone grit flying around in your new motor. best wishes
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Good advise about grit in the new motor. I have been thinking about this valve job that has gone bad in a short time. I have watched several videos on You Tube, and have seen machine shops doing valve jobs with the stones that do flathead engines on a regular bases. The machine shops say they can not do a routine valve job on the flathead block in their machine, because the block will not fit into the machine. Maybe the machine shop that did my engine did not have anything to do the valve seats with, and that has resulted in this problem. I have noticed the good flathead Ford valve tools are very expensive. If a machine shop had to buy them to work on an engine design they do not get often they may have tried some other method. Who knows for sure. I am going to do this repair the best I can and praise the Lord and full steam ahead.
 
You will prevail. The machine shop that claims the work cant be done because it doesn't fit their machine is not a flathead mechanic and should not be doing the work. A "pilot" that centers the surfacing stone or cutter runs off the upper valve bowl and the lower tappet bore to assure concentricity. That is what went wrong in the first place. Did the prior valve job use split guides? If so, mixed up halves would add to the lack of a properly aligned valve job. How do you plan to proceed if you don't mind my asking? PM me if I can be of assistance.

IMPORTANT check the old valves. Are any bent slightly? Any signs of the valves hitting the heads? There has to be a sign somewhere of why this gradually occured.
 
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Call your shop and ask. Valve seats are multi angled. If you have these questions about the valves from the rebuild, I'd also question the bore too. But don't over think it. Call the re builder.
 
Just for an update to all that have an interest. I have purchased a Black and Decker valve seat grinder to clean up the valve seats. The stone I need to do the job is the 1 5/8, which came with my unit, but has a chip on the bottom of it. Also, the set did not have the flathead Ford valve guide adaptor so I had to find one of those. I am looking to buy a new 1 5/8 stone soon and start the process of cleaning up the valve seats. I will post new information when I have it.
 
thanks for keeping us up to date. i could have loaned out the pilot, but you got one. in your case, since it was done so recent, it may not need real grinding. first thing i would do is paint the seat with a magic marker or blue, and turn the stone by hand, and see what the heck is going on. do the same with a new valve and some compound. keep in touch!
 
Ideally you should use 3 stones, 30*, 45* and 60*. This enables you to position the final seat in the correct place, as well as give you control over the width of the seat surface. Google 3 angle valve job.

Curious, did you ever check all the valves for straightness, and potential head contact?

Happy to hear your on your way to getting it fixed. Let us know how it goes.
 
Another up date if you are interested. Hooked up the valve seat grinder today with the 1 5/8 45 degree stone. The valve seats on this engine are not smooth at all with gapes all around the seats. Did the seats on pistons one and two. After grinding the valve seats I could see a big improvement in the surface of the valve seats. I lapped the new valves on pistons one and two. Valves show a very good contact patch and seal all around. Appears to me the shop that did the engine did not have the Flat Head Ford adapter to grind the valve seats properly. Just a guess on my part. Bottom end of the engine looks very good along with the very clean water ports. Will do some more work and post the results for all that have an interest. I have ordered another tool that will attach to a drill and lap the valves much better than the hand twisting I have done in the past. Be about 10 days to get the new tool. Thanks for your interest, support, and encouragement. The situation now seems to be on the up swing.
 
That sounds like good news.

The shop that did the "work" should be ashamed of themselves.

To be honest if the seats have been ground it should only take the slightest amount of lapping. It should be easily achievable by hand. Why not try the ones you have done?

Mart.
 
For those interested here is the latest with this project. Today I did the stone work on all the valve seats. The valve seats that had 60 to 65 compression needed about 7 seconds of grinding to clean them up and remove the dye. The two cylinders that had 90 compression only needed about 3 seconds of stone grinding. This engine should show a big improvement in performance now. Will do the lapping of the seats and valves when the new tool arrives. Will post new findings when they happen.
 
seven seconds is a lot. be careful, or you will end up with the seat very low on the deck. check often, i like magic marker pens
 
i gotta add some more or i will lose sleep on this one! normally, you have a spring on your pilot, and you only briefly touch down on the seat, and the spring pushes the stone off. briefly, as in, the stone cuts quick. if you are grinding for seven seconds, you cut the hole bigger, and put the seat out to the edge of the valve. and, if really grinding for 7 seconds, its darn near time to true the stone again. and theres that much more stone grit to clean up. if your motor builder guy really had the seats that far off, well maybe your new pilot is trying to make a whole new center. with the 3 different stones it can be done, but you end up lower, and lower in the deck. you want the actual seat contact about a 1/16th in from the outer edge of the valve when done, and the valve slightly proud of the deck. i hope i am telling you things you already know, best wishes
 
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If the seat is off center is one thing...but if the guy doing it with a cutter got so much shatter it´s not consistant is another thing.
I see a lot of seats coming it done with a not so sharp cutter that seal poorely...
Stones makes a beautiful job...that we use 3-angle cutters and seat and guide machines is just to cut down the time used...not that it makes a much better job...
 
cas3 said:
i gotta add some more or i will lose sleep on this one! normally, you have a spring on your pilot, and you only briefly touch down on the seat, and the spring pushes the stone off. briefly, as in, the stone cuts quick. if you are grinding for seven seconds, you cut the hole bigger, and put the seat out to the edge of the valve. and, if really grinding for 7 seconds, its darn near time to true the stone again. and theres that much more stone grit to clean up. if your motor builder guy really had the seats that far off, well maybe your new pilot is trying to make a whole new center. with the 3 different stones it can be done, but you end up lower, and lower in the deck. you want the actual seat contact about a 1/16th in from the outer edge of the valve when done, and the valve slightly proud of the deck. i hope i am telling you things you already know, best wishes
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Lot of good advise here. The 7 seconds of grinding is not all at one time. I did about 2 seconds and checked it. Still had dark spots of die. Did the grind again for about 2 seconds and still dark spots. Ended up with about total of 7 seconds on three of the seats. What else can you do if the seat does not clear up and the dye disappears? I saw no alternative but to grind the dye away. Will lap the valves and see what I have. Had an engine that would not run before with the valve seats the way they were. Hoping for the best and trying to make a better situation out of a bad situation.
 
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