Loss of compression, rebuilt engine
 

I recently rebuilt my 3.0 SC engine. I also added a BAE turbo kit. I have the following problem:

The engine is losing compression on 4-5-6, where the compression pressures are 150-135-130 respectively. 1-2-3 are at 160. I'm going to do a leakdown this weekend. Car runs good cold, sounds like a lawn mower warm. Turbo at 5 PSI boost. Plugs reveal no sign of internal damage or detonation. The 4-5-6 cylinder bank also leaks oil.

Leakdown will probably reveal whether I put the cams in correctly. I may have somehow forgotten to torque the barrel nuts. I have 993 head studs, which were, IIRC, torqued, then another 90 degrees. Engine sounds, when warm, that the compression is blowing out of the cylinder-head interface. I do not believe I have overheated the engine in it's first 500 miles. This condition has become progressively worse. I am unsure whether these studs needed to be retorqued.

I have some possible theories on what and why, but I am open to hear any other possible scenarios. Best case repair is from me being stupid and not torquing the heads correctly. Worst case is I detonated the heads loose. I am baffled as to why it only happened on the 4-5-6 side, other than that side may run hotter due to the oil cooler, thermostat, etc, on that side.

TIA
Pat

To venture a guess based on your information I have two guesses

Did you install the CE rings between the head and the cylinder? (the ones that fit in the groove on the cylinder)

Or you've pulled the head studs on that side of the motor.

As a quick check, take off the lower valve covers and see if the head nuts are loose. If they are, torque them down. Drive the car for another week and check again.

I think it is unlikely that you forgot to torque the heads correctly. If you have the knowledge and skills to install the kit, I doubt you would make that kind of mistake.

AFJ

If it sounds like 1 1/2 old VW vans, the head gaskets are leaking.

I've had 8 Microbusses, and only one sounded like that, after I blew a plug out on #3 cylinder.

AF, I didn;t find the CE rings in the pile of leftover gaskets, so I must have put them in. In order to retorque the heads, should I loosen the nuts to finger tight, and torque them as if it were the first installation? I will check on stud conditions, etc, after work tonight.

Pat

Pat,

This is very odd. I would NOT lossen them but simply recheck tourque . If you can hear Then I would be concerned. Any oil on the plugs? Is it consuming oil?? It is possible to injest oil which intern will lower octane on the A/F ratio which can cause big problems if prolonged. I don't think that is your problem though. I wish I could be more help but no guesses at this point.

When you built the motor did you check your deck height before assembly?

Ben:
This turbo crap gets pretty complicated, doesn't it?

hm, no, I didn't check my deck height as I would if building a high comp engine cause I really didn't do much to disturb the stock SC settings. I eyeballed it and determined that if anything, my CR bumped incrementally.Mine is the low compression SC 3.0. I doubt there are valve clearance issues. I will definitely know when I do the leakdown check.
Pat

I am thinking cam timing is off on the on side causeing for lower Compression numbers on that bank. that also explains the running crappy when warm. I did this by mistake on my first engine rebuild and retimied and no issues from that point on. just a little off will make a world of difference. It could dare I say cause to bend a few valves just enough to make it run crappy when warm.

I feel like we are now brothers pat. Huge learning curve ;)

Thanks for the sympathy, Ben. I know you know how it is.
I did a cold leakdown on #4 and 5. 5% leakdown on #4, 25% on #5, air coming out the crankcase breather. Had to stop the test to fetch pizza.

This is not looking good. My worst fear on every engine I've ever built is breaking the rings. I'm going out to pull the valve covers off and see how everything looks, while I try to think of any other way for air to escape out the breather if not by the rings. Maybe I'll try it again warm, but a 20% difference in cold from cylinder to cylinder is ugly, no matter how it's cut

I turboed a honda accord about 25 years ago . It doesn,t take much of a run with a lean condition to scorch the rings and cylinder bores.I think you said you were running A/F of 14:1? (Way too lean) I would guess you might even have broken rings. The telltale blowby in your previous post reminds me of a similar experience with the Honda. I couldn,t hear audable detonation either but a sustained high speed run of about 5 miles caused the engine to start blowing out volumes of crankcase fumes. We found the top inch of the bores burnt blue. We reassembled with a hone and new rings and ran richer mixtures and less advance. You might notice I also have a Corvair turbo (owned since 1972) They were engineered without a wastegate and used pressure retard and rich mixture under boost but were also prone to fits of detonation and often suffered broken rings and cracked. pistons. I hope the damage is minimal but you need to dismantle to find exact cause. Don,t run without boost enrichment and less advance as a minimum.

Johnsjmc
Thanks. I have seen similar from the VW's we used to turbo in the 70's. We'd put them on the Stuska dyno, and run em without any boost control. They could make 230 HP, fail, but they were just little junk 1600 engines we tested with. Unfortunately, I don't recall details of 25-30 years ago as well as I should (but I'm sure I was having fun!)

So, I went back out to do a bit more testing. I drained the oil, no magnetic bits in the sump. I pulled the exhaust valve cover off 4-5-6. The head studs seem tight. Valve clearances on the exhaust were good. I leak tested #5 again, still cold, but I turned the engine by hand a few times prior. Now, I have like 1% leakage. I tested #6, negligible leakage again. I think next week I'll have to run the engine and get it warmed up, and leak check it again, unless I do it tomorrow.

I'm starting to get a bit baffled by this, but the warm test should be definitive. I initially am thinking broken rings also, but have trouble figuring how the little bit of boost did this, unless I broke them during assembly. I did check the end gaps on a few of the rings, but not all. The ones I did check were good, so I didn't feel it necessary to do them all.

However, detonation is a different story. Again, I have a water injection system set at 3 PSI which should limit the detonation (that's why I installed it). Plugs do not indicate any detonation at all.

Thanks to all of you guys for the help and ideas!
Pat

I am not to be listened to but my guess is cam timing? Just wanted to subscribe. I read on the engine rebuilding board about similar symtoms from experienced (somewhat) people.

Can you hear where the air is rushing to during the leakdown? There are only 4 places for the air to go; intake valve, exhaust valve, headgaskets,or past the piston. You may be able to listen in the exhaust, open the butterfly and listen to the intake, and take off a breather hose or the oil cap and hear where the air is going.
Good luck!

Warm leakdown test results:
1-2-3-6 all less than a couple of percent
5 has about 5% past the rings
4 has in excess of 25%, past the rings (90psi/68 psi)

Either the ring(s) broke, or they didn't seat. I hate when this happens.

I've had problems with using synthetic oil too soon and having the rings not seat. I'm sure that others here have used synthetic from the beginning and had no problems, but maybe you could satisfy my curiosity, what kind of oil were you using?

20w 50 dino, Cam 2 to be precise. Oil may be a bit heavy for break in WRT rings, but it's better for the cams.

pat I have 90 warm on one of my cylinders and my engine is smoked I am afraid you may have done the same

I would guess broken rings, time will tell. I think with poorly seated rings you would see 15% at the worst.

Cheers

Ben
90 was the leakdown test pressure, of which it retained 68, or a 22 PSI loss. The warm compression pressure was 160 PSI.

I'm going to have to take the top end apart and see what's going on in there. Maybe next week when I get back from the Glen.

The engine still runs ok, but it needs to be fixed before I do smoke it.

oh got you.. Man You know how it is missory loves company:D