compression test

3361 Views 3 Replies 3 Participants Last post by ghnl, Apr 20, 2011

Huzz

Discussion Starter · Apr 20, 2011

I did a compression test on my 1990 spider and the results seem too low.
105,100,105,100
Can the VVT have anything to do with the readings?
The car runs great, I feel it has plenty of power, but I used 1 qt of oil on a 250 trip. It does not smoke or have any external oil leaks.
I have only driven it 500 since I purchased it a couple months ago. The oil is crystal clean, so clean I was thinking the previous owner might have had the engine rebuilt. Thats why I did the compression test. I thought maybe the rings have not seated.
Or maybe the rings are worn out ?
What should the correct readings be and is there a special procedure for checking?

Save

1 - 4 of 4 Posts

Tifosi

· #2 · Apr 20, 2011

Didja have the throttle WFO while checking?

If the engine is fresh, the rings should be mostly if not completely seated by 500 miles unless they were initially bedded poorly or the parts weren't uber clean during assembly or some twit lined up all the ring gaps in a fit of uniformity OCD.

VVT will have a very small effect, but not as radical as you're showing.
(I wanna say 150~180~ish for VVT equipped and 180~200 for non~VVT, but my memory is kinda dim this time of day)

On the flip side, while your your numbers are very low, they are all within 5% of each other which is a good thing.

Save

Huzz

Discussion Starter · #3 · Apr 20, 2011

Yes, the throttle was wide open and I even checked it with another known good gauge.
Same reading. It does raise with a squirt of oil 20 or 30 lbs.
It's kind of wierd that the performance of the engine is OK.

Save

ghnl

· #4 · Apr 20, 2011

There are a couple of unknown variables - the accuracy of the compression gauge & the strength of the starter/battery.

250 miles/quart of oil is on the high side. You may not see clouds of blue smoke but if it is not leaking it must be burning oil. If it otherwise runs well just make sure to check the oil level frequently and keep it topped up.

Perhaps an "Italian Tune Up" might help clear/seat the rings? See engine break in secrets. FWIW, when I rebuilt the engine in our MGB a few years ago I drove it gently for a few hundred miles thinking I was breaking it in gently. I was not happy with the performance & oil consumption however. Then I read the above link and decided to stop babying it. Within a few hundred miles the performance noticably improved and oil consumption dropped (except it still leaks a bit...).

See less See more

Save

1 - 4 of 4 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month