engine trouble, need advice

[recordsj]

1500 MG Midget

On a drive I had some engine trouble.

On idle the car dies and I have to pull the choke a bit to keep it running at idle (before the issues, I didn't need to do this).

I also had some smoke from the bonnet (from some oil spewing out from somewhere). Burned about 1qt of oil in 15 miles.

Pulled the spark plugs and all 4 are covered with burned oil.

I did a compression test and saw the following on both dry and wet compression tests:
cyl 1) 120 psi
2) 140
3) 90
4) 140

I also did a vacuum test and at idle I saw 15 inHg which it fluctuated about +/- 1 inHg steadly.

Unfortuatly I don't have readings on the engine before this issue came up to compare to.

Any thoughts on the issue?

 

[Jim_Gruber]

I see a valve job and possibly rings in your future.

 

[recordsj]

if it is valves or rings, wouldn't the vacuum reading be more than fluctuating +/- 1 inHg?

 

[recordsj]

after running the engine with the hood open running my tests some more, I noticed the oil coming out is from the dipstick tube when reving the engine.

I did check the PCV valve in which it is operating correctly apon inspection, then cleaned it out and reinstalled it.

After reinstalled it, ran the engine, then oil came out again after reving the engine.

Any thoughts on what the root cause of the issue?

 

[recordsj]

A thought I had...
if it is a valve, lets say an exhaust valve, could exhuast gas leak past it into the crankcase and cause pressure in the crankcase. In which then that exhaust gas is what is causing the oil to be pushed out of the dipstick tube when the engine is revved?

 

[SilentUnicorn]

sounds like a toasted valve. can you do a leakdown test

m

 

[recordsj]

From what I have read about the vacuum test I should be seeing more of a fluctuation of the vacuum reading if it is a valve issue.

But from the compression test it does point to a valve.

I don't have the equipment to do a leakdown test.

 

[Guest]

Set the valves and check comp again. I had crossed up plug wires once that gave me bad blow by, but my motor was preety well shot too. Pulled the choke? What carb you got?

 

[recordsj]

I have already checked the valve lash.
Then engine was running fine, then it started to have problems (i.e. I wasn't just working on it to have caused the issue to appear).

I have a weber dgv carb.

 

[SilentUnicorn]

is/are the carb and manifolds tight? no leaks any where?

 

[recordsj]

not seeing or noticing any leaks (sprayed brake cleaner around the intake manifold gasket and carb gasket). Plus if the issue was just a vacuum leak, I wouldn't be having the issue of loosing oil....

But I am suspecting there is indeed something wrong with a valve with the low compression reading in cyl #3 (90psi). But having 15 inHg +/- 1 inHg vacuum reading, I would expect this to fluctuate more if there was a valve problem. Or would I be assuming incorrectly?

 

[recordsj]

If I am getting excessive blowby, wouldn't that lead to mean that it is a piston ring issue and eliminate the issue of an exhaust valve problem?

 

[jlaird]

I would suspect rings, do a compression check. Cheep and fast.

 

[recordsj]

I did do a compression check (both dry and wet). For the wet test by squirting some oil into the cylinder, I did not see any difference in the compression results of:
cyl 1) 120 psi
2) 140
3) 90
4) 140

Which led me to think a valve issue.
But I am getting some exessive blowby (oil is coming out of the dipstick tube), which leads me to think it is a piston issue. The test results are a little confusing of what is going on and what the root cause is.

Any insight?

 

[Billm]

You could have easily cracked a ring on #3

 

[recordsj]

I did a compression test and saw the following on both dry and wet compression tests:
cyl #1) 120 psi
#2) 140
#3) 90
#4) 140

I have seen oil come out of the dipstick tube when the engine was running (none coming out during the tests).

But when I did a vacuum test, it held steady @ 15 inHg, but jumped +/- 1 inHg.

the leak down test showed a 40-50% leak rate on all cylinders(I have a two gauge system from Harbor Freight). In doing the test I did make sure the valves were closed (opened the valve cover and checked to see if I can move the rockers).

I feel air coming out of the dipstick tube, no noticable air from the carb, hard to tell if any air is coming if at all from the exhaust (the exhaust manifold is still connected with the engine in the car).

Any thoughts on the root cause? I would of expected a much higher leakage rate out of cyl #3.

 

[recordsj]

I reran the test after realizing I had a broken gauge. Found a high leakage rate on #3 as one would expect and it looks like bad piston rings or cylinder bore.