Scratched valves

I

iKst

Member
Hey,

my car was smoking badly especialy around 2000rpm with very little throttle. It puffed BIG clouds of smoke in idle at that engine speed, otherwise it wasnt that bad. Also, compression was a bit poor, 10 bar on the best cilinder and less than 9 on the worst. All this around 5000, 6000km after engine rebuild.

Today the head went off and i took the valves out. I didnt notice anything special. Cilinder walls were clean and smooth, i poured some gasoline in cilinders and it drained down to sump completly after an hour or so. But i did notice a lot of oil around valves on 4th cilinder. I took the valves out and after close inspection i noticed they are scrathed on the top side.

When engine was rebuilt i also had my head and valve seats fixed. So i guess then damaged the valves there, when they did seats. There is a picture below, its not quite clear (shite camera) but you can see where the damage is. The theory is that scratched part of valves damaged valve seals and oil could get past them. Is that possible ? Please tell me that is my problem, otherwise its engine out job again.

valve.jpg
 
Might be a leaking valve stem seal rather than the valve itself. The area youve circled only has the valve spring round it so I dont think it matters.
 
Thanks...thats useful.

Valve seals look nice and soft, so i dont know if thats is a problem. Any ideas why its smoking so much (there was alot of oil in comb. chamber in head on 4th cilinder) ? Could timing cause smoking. Mechanic said that belt seemd to be 1 tooth off, but he wasnt sure.
 
1 tooth out shouldnt make that much difference, it varys with different cars. all the tooth out will do is advance the timing slightly and to a certain degree the engine should run better. however if its a tooth out in the wrong direction you will get pinking or detonation which will cause the smoking.
 
Might be the oil scraper ring is shot in #4 but compression rings are OK. What was the compression on #4?
 
iKst said:
1. 9.5
2. 9.1
3. 8.6
4. 8.1
Click to expand...

Those are all pretty low mate. You should be seeing 10 bar minimum. You did do the test with the engine warm, all plugs out and throttle open? Did you try putting a bit of oil in the bores to see if the results come up?
 
I know 10 is minimum, and it should be even better with new rings.

Engine was warm, all plugs out, throttle open... A friend who works in VW garage did this test on their pro. testest. We didnt have time to do wet test. At home i did a test again with that manual tester and results were a bit better, but still last 2 were below 10. I tried wet test, but i got almost 15 bar and 4th and almost the same on other 3. I did this the first time, and i realy dont know how much oil to pour down the cilinder so i didnt think the test was realistic.

If the rings are gone, does anyone know the reason. I mean...they are only 5, 6kkm old so there must be something vrong with engine. I know its hard to say, but is there a commom reason for this ?
 
Should be about a teaspoon of oil in each bore for the wet test.

I can only think that either the engine wasnt run in properly.
 
I did what manual said. Slow engine speeds etc for cca 1500km. But i used syntetic oil when running in. Could this be the case ? I know now i should only use mineral oil for first few 1000km. Could this make such a diference ?

Btw...if i change rings, do i have to hone the bores again? They were honed once before (pistons are still std. size). How much larger does the bore actualy get with honing ?
 
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