leaking valves, low compression one cylinder.. .

Faustus · #1 (**permalink**) 03-03-04, 07:07 PM

'81 Coupe DeVille V8-6-4 368cu w/ TBI, automatic

had a rough shudder when in gear so..

did a compression check on all my cylinders... every cylinder was around 115 on the initial turnover, then peaking out at 155 after 7 turnovers..

except one cylinder which was at 65 first turn, and barely moved after 7 turnovers. also all sparks were clean except that same cylinder, lots of black gunk... (haynes *crapey manual!* tells me problem is a leaking valve.)

at this point, mechanic is telling me im basically hooped.. to go for rebuild, or new engine.

i can get a rebuild done for approx $1500 CAD.. or alternatively im being told i can bring my cylinder/valves into a rebuild shop and they will do a "valve grind" for $180. im not sure what is involved with that, so im kinda looking for a basic run down on the procedure from you guys. im definately not going to dump $1500 into getting the engine rebuilt, when i can just go buy a new engine for $600 less. but the valve grind sounds possibly promising.

could someone possibly take a moment and explain (ballpark) what are the things involved with getting to the pieces i need to take into this shop for a "valve grind"? not specifics, i can get a manual for that.. but just an idea of the work that is involved.. and do-ability/practicality in it.

im so close to the point where i could sell the car and get what i can for it... or dedicate some time and money.. i love the car dearly, but i have to be practical at the same time..

thanks! and thank you to everyones help so far with my inane, amatuerish questions, its appreciated

DaveSmed · #2 (**permalink**) 03-04-04, 02:39 AM

All you would need to bring is the heads. The valves are removed, and are installed in a valve grinder (kind of a cross between a bench grinder and a drill) The drill part is held at the angle specified for your valves, and it spins as the grinding wheel cleans and trues the face. This is provided that the valves are not excessively worn. With the valves out of the heads, the seats also get a similar treatment. When this is done, the shop usually will put shims under the valve springs to compensate for the material removed. This is also a good oppurtunity to check your valve guides.

Imprl59 · #3 (**permalink**) 03-04-04, 02:24 PM

You really haven't done enough testing yet to determine the problem. You know you have an issue but it could be many things... Bad valves (as you suspect) bad rings, bad cam etc. I would reccomend that you do a leak down test to pinpoint the problem. Here's an explanation of a leakdown test http://www.autosite.com/garage/repairqa/ques057.asp

Also how many miles are on the engine? On a high mileage engine if you just redo the heads you stand a very good chance of creating an oil consumption problem. Basically once the heads are redone you have a brand new top end but the rings are still old and worn. This can cause oil to be pulled past the rings and burned when it wasn't doing this before. I have tried redoing heads myself twice and been very disappointed in the end result.

Steve B.

Faustus · #4 (**permalink**) 03-04-04, 05:59 PM

thanks guys, very usefull info...

Imprl59; the exact miles im unsure of, because my speedo is reading 41k, i do not believe it has gone all the way over, but something happend at a point in time prior to me owning the vehicle, maybe they did a rebuild and turned the clock back, im not sure.

the oil consumption thing was brought up by the guy that mentioned the valve grind... so definately, yes ill go for the leakdown test first.. get a good idea of exactly whats occuring and go from there.

DaveSmed; thanks for you info too mang

DaveSmed · #5 (**permalink**) 03-05-04, 01:39 AM

Since it looks as if you already have the compression tester, why not do a "wet" compression test first. Squirt some oil in the cylinder, then do the test again. if compression comes back up, its not the valves, its the rings. The leak down is also a good idea, and I would recommend it if the wet compression test produces no change.

Faustus · #6 (**permalink**) 03-05-04, 05:31 PM

Quote:

Originally Posted by DaveSmed

Since it looks as if you already have the compression tester, why not do a "wet" compression test first. Squirt some oil in the cylinder, then do the test again. if compression comes back up, its not the valves, its the rings. The leak down is also a good idea, and I would recommend it if the wet compression test produces no change.

awesome. ill try that first. thanks again for your help... i just hope i can get through this with minimal costs and scrape by.. i dont mind dedicating the time, but im not a rich man heh