Engine condition, Compression/leakdown

[andyblackman777]

Hi all , I'm after a bit of advice,

I've pulled the engine out of my car to do some work which requires its removal. The engine runs perfectly. Before I did this I ran a compression check which showed all cylinders evenly low, which is bad.

Now the engine is removed I performed a leak down test this shows on between 5-10 percent leakage on all cylinders, which is good/ok.

I then performed another compression check now I'm getting 125 on all 4 on the left bank and 130 on 3 and 140 on the remaining cylinder on the right bank. Should be 150 +/- 10 %

Now I'm in two minds as what to do. leave it or rebuild it. Bear in mind I have another engine stripped that I was going to rebuild and swap with the current engine. Plus is 3-4k just on bolts, gaskets and bearings if nothing needs replacing!

Im tempted to do what I originally planned and put this motor back in the car. Hmm

Thoughts

Cheers 

Andy 

[Escape]

Did you have the throttles fully open when doing the compression test? Usually a leak down tells you more about the state of the engine. That seems good, so a big problem seems unlikely. Apart from the one at 140, all cilinders are very similar as well.

So I'd be tempted to just put it back, especially as you say it was running perfectly and you have another engine to rebuild.

Filip

[Thartje]

Should be doing a compression test on a hot engine. Not sure if you were able to do that with the engine out of the car.

[andyblackman777]

Yes wide open throttle.

I did both, while it was in the car, all between 100 and 120 best. the hot ones were not much different. Odd now they seem better when its out of the car and stone cold.

I assumed it was maybe on the way out and only did the leak down to see where the air was leaking from. When the leak down didn't seem to bad I though id re check the compression and it was 20 % higher on all cylinders.

[Erikl]

Is it possible the timing is off slighty some how and valves are a wee bit open screwing up the comp test?   Maybe check that the exh and int timing is 100%.  Cant imagine off a tooth but isnt there a part in the cam belt system on V8 that can get loose and slip and folks drill and add a key.

[andyblackman777]

Erick

That's what I thought could be the problem but alas it wasn't. first thing I checked. easy job with the engine out. tolerance pins fitted with the crank Locked against the marked vane. Also if this was the case the air would be escaping from the valves on the leak down test.

 

[Erikl]

Oh I remember what I was thinking

 

on the air cooled 911 if the valve adjustment was off a bit it could make a bad compression but the leak down would be good because you can rock the motor back and forth a little until you get the valves to seal

could it be valve lash

sort of same thing but throwing mud 

[910Esprit]

Just forget about it and put it back on the road.   Could well recover after some regular use and low compression is not risking engine failure.

[andyblackman777]

Yes I did wonder if it was due to lack of use. Or the Gauge...... 

[andyblackman777]

I decided to take the engine apart to inspect it. I'm glad I did. it was previously rebuilt for low compression years ago and I was never overly confident with the build. I took the head off on the side with the lower compression readings. I found loads of silicon still in the waterways, one piece was about 6 inches long and was totally blocking the turbo feed.  A wasp stuck in the head gasket nicely preserved after 20 years! also the bores had been 'honed' but without moving the tool up and down so just lots of horizontal score lines. Also the block had had the old gasket material aggressively scraped off. Cam journals and bearings scored and one cam cap in the wrong place.To finish the head is warped too.

I wonder what the other side is like . hmm......

 

[LotuStuart]

Yikes!
Name and shame?

How the F did that wasp stay like that??

[andyblackman777]

It was 24 years ago I bought the car from a performance car dealer down on the south coast uk. I had problems with the car and the garage they used rebuilt the engine. Mind you it has ran ok all the time.

maybe the glycol is a preservative?? Or Im wondering if it had got in the cooling system whan I changed the radiator and some pipe work a couple of years back??.

[andyblackman777]

Update on the low compressions. The gauge was reading low. Bit of a story, I was selling my old Aprillia race bike which I couldn't get started (no fuel). A guy came to look and said he would have it if the compressions were ok. I checked them with my gauge and they were 180 psi. He had brought a gauge with him and used that and it read 220psi. which is the correct pressure for that engine. He bought the bike and kindly gave me the compression tester. ( we'd had a long chat about the Lotus). I'm glad I have taken it apart though. I think it would have not survived much longer

 

More inspection fun, I found an another piece of metal this time inside the cam where the pulley bolt goes in. Some sort of pin used I assume to try to lock the cam when tightening said bolt. Obviously the tip of it got cut off and luckily remained inside! Also some  metal inside the water jacket, looks like silver solder?

Interestingly the cam pulley bolts had traces of oil on them along with the friction washer and cam pulley mating surfaces. no thread lock and weren't very tight either! I'm amazed none of it ever slipped. All the intake valves had been cleaned with a wire brush to the extent that the stems were badly scored around their circumference  where they run in the guides. Luckily I have another set of heads which are nice and flat and are  at the machine shop getting seats and valves re-cut along with the camshafts having the  journals polished.

Bottom end seems ok crank pins are fine and the crank spins nice and smoothly. 

I've measured the old pistons and liner bores and they are not that worn, 2 thou clearance on the trust axis compared to 1.25 thou on the new ones.

I think the compressions were uneven due to poor ring seal with the weird Honing and the top end having poor valve seal. The heads were a mess.

The wet 2nd compression test did yield higher results.

Interesting the leak down test was ok ish, I guess they run just fine with poor sealing, just don't make the power....

 

Anyway Had fun measuring and all my new bits arrived today so can start rebuilding next week I hope.

 

 

 

 

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