m20b20 time for rebuild?

[Brdjo]

I need your opinion on this one..

I have '88 , M20b20, 206 EE engine, 8.5:1 compression ratio, with 230 000km on it..

My problems are:

1. Oil consumption, 200ml on 2500km. (Elf Evolution 700 STI 10w40, and same consumption with Total Quartz 7000 10w40) also little bit oil leak on sump gasket..

2. Build up some oil in air intake rubber hose, guessing it is coming from breather hose, caused by piston ring blow by?

3. Fair amount of light blue smoke on warm startup after 45 min standing, bad valve seals and valve guides?

4. When the engine is fully warmed up and running, pulling out the dipstick, and some kind of smoke coming out. Piston ring blow by?

Did compression test, dry and wet, almost same results (0.1 and 0.2 difference on wet test, 1 and 5 cylinder):

Dry, fully warmed up:
1= 6.6 bar
2= 6.7 bar
3= 6.8 bar
4= 6.9 bar
5= 6.6 bar
6= 6.8 bar

Did anyone knows is this too low? And how much bar is ok?


My plans are to take the head off and replace valve seals and valve guides, and then i will have a look on bottom end as well.. Not keeping my hopes high for the bottom end, but just wanted your opinion on this one..

Thanks

[pianist]

Usually its between 12bar and 14bar what you looking for and when you doing the test make sure TB is fully open, by what you described it doesn't look good, best scenario is your rings are stuck in piston grooves caused by oil contamination worst: rings broken and cylinders scored. Gl with it pal

P.s. can you smell petrol in oil?

[Brdjo]

Wow 14bar? I was thinking that they are come from factory with 11 bar max.. TB was fully open ofc
Yes, little bit of petrol can be smelled on dipstick, and on breather hose, witch is vented to atmosphere.. Which indicates poor rings..?

After taking head off and measuring cylinders we will see, just hoping that the block still have possibility to be bored to next ring specification..

[pianist]

Like I said it just might be a stuck rings in piston groove cause of oil burning, hope for the best but prepare for the worst

[Brdjo]

Thanks for info so far I did not keep my hopes high
Did some research on parts price for proper rebuild, and I can tell you that everything smells on m50 swap xD

Anyone else on the subject? Can anyone confirm bar values for m20 engine? And how much bar should make healthy m50 engine?

[reggid]

those compression numbers are low but they pretty consistent and adding oil doesn't change them much so im inclined to think the bottom end may not need to be rebuild just yet. 200ml in 2500km is not enough to warrant a rebuild IMO. do the headjob and see what it fixes

An m20b25 is typically 10-11b or so with alot of miles

[Brdjo]

Thanks for reply reggid..

The head must come off that is for sure.. still I can not see how the head can drop so equally pressure, but also that much compression loss must results in way more oil consumption, I think?

Guess I will wait for couple of free days to deal with it, and I will keep you posted..

[reggid]

most people dont seem to realise that the compression test or leakdown tells you little to nothing about the oil rings. the oil rings are separate from the compression ring(s).

as an extreme example f you have an otherwise healthy engine and remove the oil rings then the compression and leakdown will still be ok but it will eat oil in a bad way. the same if the oil rings are mint but there is something wrong with the compression rings or ring grooves the comp test or leakdown will show an anomoly

[Brdjo]

Thank you very much for reply...
as soon as possible the head will come off.. hoping in next 2 or 3 months the weather will allow to get job done.. I will keep you guys posted.. till then it's e30 snow time

[Yeti]

i reckon the valve seats are leaking. have you done a leak down test?

[Brdjo]

No, I only did compression test.. I don't have equipment for leak down test available, but maybe I should get one. Leak down will definitely tell more..

Funny thing is that car has no problem starting on -22 celsius or eny cold start, i was expecting bit of struggle but it's starting like a charm..

[Brdjo]

Just a little update, yesterday I took a compression meter from a friend and it turns out that the first one that I use was broken and showing false reading..

Dry, fully warmed up with second gauge
1= 12.5 bar
2= 12.5 bar
3= 12.6 bar
4= 12.6 bar
5= 12.5 bar
6= 12.6 bar

So, all along I base my conclusions on false reading from first gauge

And the warm start up is probably the issue of bad valve seals, oil gets in the combustion chamber and the fun begins..

[Brianmoooore]

It's possible to change the change the valve stem seals without removing the head, using coiled up string or compressed air to keep the valves in place.

[Brdjo]

It's possible to change the change the valve stem seals without removing the head, using coiled up string or compressed air to keep the valves in place.

Did not know that is possible.. Seems like a painful job. Can you walk me try procedure, in help of better understanding how it works?