Poor compression.

[chrishewett]

Having just got my +2 back on the road after 6 years I decided to test the compression. I was horrified to find it very low. The best figure I obtained was 145 on number 1 and the worst 75 on 2. The engine was rebuilt about four years ago but I only drove it for about 400 miles in about 6months and then it was not driven until the other day. It starts and runs fine but I have only tested it for a couple of miles. I tried putting a little oil in the bores and the figures showed no real difference but then was only 115 on number 1, number 4 went up from 115 to 135.
The engine was rebuilt by a local garage with new oversize pistons. The head went of to PNM engineering for a skim and full rebuild.
Could these figures improve with driving?
The best hope is that I messed up the test. I borrowed the tester from a local garage , it screws into the sparkplug hole.
Can anyone give me some advise please.
Chris

[cliveyboy]

Chris
When I do a compression test I push the accelerator pedal right down and spin the engine. If you do not keep the carbs open you can get funny readings.
Cliveyboy

[types26/36]

Chris
If you do not keep the carbs open you can get funny readings.

Engine must also be at operating temp.
Brian

[Hamish Coutts]

Chris,

I would try putting WD40 down the bores and leave it for a wee while (1 hour) Then spray a bit more down and start the car. I've freed up quite a few stiff rings this way.

Like Cliveyboy says make sure the throttle is FULLY open and the engine is at operating temp or thereabouts. Also the battery needs to be good so that you get a decent crank from the starter.

160 and above is OK.

I did he same thing about a month ago and got 190, 190, 190, 90 and my engine was rebuilt by a local engineer about 15k miles ago, not long before I bought the car.
The rebuild was crap (it was rebored 7 thou too big - you wanna hear the liston slap!) so I'm just about to do it myself. Just got the block back from reboring and crank, crack testing and polishing. Hope it works better this time.
Hope you don't have to be this drastic!!

Regards,

Hamish.

[Hamish Coutts]

Chris,

Just read your post again. The variation in compression could be due to gummed up rings. Try the WD40 trick 2 or 3 times and use quite a long squirt down each plug hole (e.g. at least 3 seconds). Also try cranking the engine with the plugs out after you have put in the wd40. In 6 years the oil and other crap in the rings could have dried out to a goo and cloged up the rings. With any luck the wd40 might wash this out and give them a chance to operate properly.

Just watch you dont put too much in and thin down the engine oil.

Best of luck.

Hamish.

[chrishewett]

Thanks for the tips sofar. I will go and follow your advise. The gummed ring theory sounds likely.
Chris