Cylinder #1 low compression

[phaetn]

I just bought a '74 small bumper Spider. Body looks in good shape. I was able to look under the car when it was on a hoist and it seems decent.

Engine is leaking a lot of oil, however, and some coolant is pooling on the head, too. Hard to tell if oil is from the head gasket (which P.O. indicates has previously been replaced within the past few years) or from the cam covers that have a ton of sealant used. There's definitely oil pooling at the spark plugs, but I haven't isolated the source yet.

The engine is a 1.8L with Mark Allison's distributorless igntion and an EMPI 32/36 carb. It has a 4-2-1 manifold/exhaust and is a straight through pipe with no restrictors until it gets to the muffler at the back.

The car really hesitates at 1/2 to 3/4 throttle at around 3500rpm and spits a bit, with a backfire now and then. Wasn't sure if it was weak spark, too rich, or what. It seems solid at idle and okay if throttle isn't mashed too much and the car is gently brought up to revs. This was the first time the car has been driven this year so gas might well be old, tired plugs etc, and I don't believe it was really driven much of last season if at all since registration was old on the plates. I pulled plug from cylinder #1 and it was very sooty but I figured it may just need to be dialed in since the car hasn't been run in a while.

Since the car was at the mechanic's to get safetied to transfer the title I asked him to check compression:

Cyl 1 - 105psi
Cyl 2 - 130
Cyl 3 - 130
Cyl 4 - 130

The 130s all seem within spec: 130/14.7 = 8.84:1 compression ratio. Different sources claim different numbers, but for a 1974 1.8L I think that's decent enough. #1 cylinder is clearly low and a cause for concern. Given that it's not two cylinders beside each other both with low readings, I gather from the workshop manual that it might not be the head gasket (which I guess would commonly fail between cylinders and seems to have previously done so between 2-3).

I didn't see blue smoke from the exhaust, but I guess I should check the rings with a wet compression test with a tablespoon of oil and see if that brings the number up. If numbers still say low then what - valves?

Anything else to look for? The coolant leak concerns me. Can it be linked to the compression? Not sure how the plumbing works for that...

The car's not home yet as there's a leak likely at/near the manifold that is letting exhaust gases get into the cabin and is a safety issue so that needs to get looked at before I can even get the car plated... Then I'll coax it home and go from there.

[azruss]

may want to retorque the head. sounds like you may be running lean. give the carb a good clean, new or cleaned up plugs. If oil is pooling in the spark plug hole it is probably from the cam covers. also make sure the plugs arent loose. If it is a head gasket, the leaks will be below the manifolds. coolant leak up high could be any of the hoses going into the head.

[majicwrench]

Sealer everywhere == incompetent repairs. Don't bother w a wet compression test, won't tell you anything. Car will never run right w that one low cylinder. I would check valve clearance first, if it's OK time to pull head.
Sounds like a project. Good luck!
Keith

[wizard124]

There doesn't seem to be good info on what the stock compression numbers should be. At least, I haven't come across them. When I bought my '80, l did a comp test also. My readings were in the 150-155 range (cold engine). Being satisfied, I have not had to do any major engine work.

I would do a wet comp test to try to ascertain the condition of the rings. Easy to do. With all the head leaks, etc I would pull it and make it right. Maybe pull the block depending on what you find with the head. How many miles on the lower end?

[majicwrench]

Wet test, when is the last time anyone has done one and learned anything?? Results are incredibly subjective. I do this for a living and haven't done a wet test in decades. I have to do things that get results and not spin my wheels.

[V12StealthHunter]

Wet test, when is the last time anyone has done one and learned anything??

About 2 months ago I did one on a 2006 Jaguar XJR that had overheated and dropped a valve seat over cylinder #4. The owner was told by the dealership to replace both cylinder heads. Not knowing any better, she replaced both at a cost of about $10k. After she got the car back it would throw a CEL for misfire in cylinder #4. So I did a dry compression test and got ~150psi on all cylinder except #4, which showed 90psi. Did a wet test and got 140psi on cylinder #4. So it definitely was useful.

You might want to ask the previous owner why he recently changed the head gasket. Did it overheat? Also who did the job.

Put new spark plugs in and see what #1 looks like after a while.

Given how small these engines are, you could completely rebuild it and have it back in the car before the snow fully melts in Ottawa. And given what you paid for the car, I think you'll still be smiling when its done. I've always used Hosie & Brown near St.Laurent Blvd for my machining in Ottawa. Intelligent people. Good prices.

[majicwrench]

So what did that show you on cylinder #4?? That the compression goes up when you add fluid to a cylinder?? Did you do the same w the other cylinders to have something to compare it to?

Take any cylinder, test compressin, now add fluid, test again, guess what, it goes up. You would need to do this a LOT to get any decent info out of it.

[V12StealthHunter]

Did you do the same w the other cylinders to have something to compare it to?

Yes I did. And the other cylinders were within 5psi. Whereas #4 went up 50psi.

[So Cal Mark]

your mechanic should do a leak down test, that will tell the reason for the low reading

[phaetn]

Thanks for all the replies, gents.

V12StealthHunter, it sounds like you know Ottawa. Flurries today. Things are going to get warmer very soon, though. Thanks for the head up re. the shop.

Right now the car is getting a crack in the exhaust manifold welded, then I'll bring it home next week and start sorting things out. New plugs, fresh tank of gas, and I'll dig into the carb. I'll find a balance between how much work I want to do and how much to have someone else take on.

Mark - one quick question for you since the car has your Compu-Tronix ignition module: I know NOT to test for spark by grounding a plug on the block as it can fry the control module, and instead just use a timing light with a clip and the lead and see if it flashes (twice since it sparks once per rev and not only on the compression stroke).

I know spark plug gap is 0.045". Any recommendations for type of plug? is it worth going for Iridium or it is just a waste of money?

[V12StealthHunter]

V12StealthHunter, it sounds like you know Ottawa.

I lived in Ottawa for 8 years. I went to the Telfer School of Management at Ottawa U and I worked in Kanata. Got tired of only being able to work on my projects for 4 months a year, so I moved to California. I got rid of most of my toys there but I still have a super clean 1989 560SEL sitting in storage should anyone be interested.