22 replies to this topic

[jime17]

Hi,

998 auto 1990.

As mentioned on a previous thread, I've got low (50psi) compression on cylinder 1. It was running fine just a bit lumpy when stationary with drive selected but otherwise fine. No real lack of performance.

I changed HG hoping hat was the issue but to no avail. Head and valve seats look ok

I adjusted valve clearance to 12 thou and re torqued head bolts after 1st heat cycle

A new problem has occurred though. Drove to work ok. Drove home ok. Got back in 15 min later. Still hot. Just turning over without starting.

I did get it started eventually but it took a long crank and reluctantly just about started. I drove round he block and stopped engine. Same problem on starting.

The plugs are a healthy colour and I've re checked the valve clearances.

Could it be this that's causing my problem? I found it more difficult than I anticipated to get a consistent gap on all rockers.

The only other thing I did was change the manifold gasket.

starting when cold is fine.

Thanks

Jim.

Edited to remove my waffle.

Edited by jime17, 16 April 2014 - 06:38 AM.

[timmy850]

So have you fixed the compression problem? New set of rings or anything?

[jime17]

No. I just don't have the time, knowledge or the facilities to pull an engine out and split it in a reasonable timeframe.

I know that is ultimately part of he solution, but it's puzzling me that before I changed the HG it was still starting and running more or less fine.

[timmy850]

Assume the head gasket was fine before, and it's fine now.

If the rings are on the way out, it's going to only get worse. It will end up scoring up the bores.

The engine will still run on 3 cylinders, but it won't like being under load.

[Dusky]

If you can, I would get the engine out and.a new/secondhand in if its your daily..you can swap engines in a weekend,and you can repair the other one while still being able to drive..

[jime17]

Assume the head gasket was fine before, and it's fine now.

If the rings are on the way out, it's going to only get worse. It will end up scoring up the bores.

The engine will still run on 3 cylinders, but it won't like being under load.

Yes head gasket was fine. Obviously changed it any way. still have same compression readings on all cyl.

to be honest I think the gearbox has seen better days quick is part of the reason im willing to drive it like this until I can get a replacement engine and box. probably a manual.


So anyway, could incorrect valve clearance cause hot starting problems as described?

[timmy850]

If your valves aren't seating properly or closing fully, or you have a crack in the head, you would have reduced compression on that cylinder.

 

If you are confident in taking off the head again, you could pop down to an engine shop with it and get it checked out?

[jime17]

Hi, yes you're quite right.

Sorry maybe with all my waffle at the start my questions been hidden.

To clarify, something I've done has caused the problem with starting when hot it would seem.

are the valve clearances that critical that it would cause this problem if they are very very slightly innacurate. Not loads out. I'm wondering if I've not done it quite right.

Otherwise im at a loss. This problem wasn't there before I changed the HG.

Edited by jime17, 16 April 2014 - 06:30 AM.

[timmy850]

No compression in one cylinder would cause running problems. Until you work out what is causing that, you're going to have issues with running and starting...

 

It could just be that your compression problem has got a lot worse since you changed the head gasket

[jime17]

Ok point taken. I just am dubious that its started this straight after and its been fine in the 200 miles prior to me changing HG that I knew of the compression loss. Obviously im no expert though which is why im here asking.

Im pretty sure its rings. It went from 50 to 70 psi when I added a dash if oil. I can also feel crank case pressure puffing out of the oil filler opening.

It is firing on all 4 as the plug on 1 is a good colour and the rpm drops when I pull the lead off. Its just obviously not as efficient.

Thanks for your help.

[Gremlin]

Did you accidentally touch the carb adjustments or the distributors been knocked round by accident somehow?

[jime17]

Did you accidentally touch the carb adjustments or the distributors been knocked round by accident somehow?

Only touched the carb by disconnecting linkages. Didn't touch timing.

[M J W J]

Pour a small amount of oil into the cylinder that has low compression and re do the compression test. If the readings are higher then it would suggest that your rings are shot. If not then start looking elsewhere for the problem.

[jime17]

Pour a small amount of oil into the cylinder that has low compression and re do the compression test. If the readings are higher then it would suggest that your rings are shot. If not then start looking elsewhere for the problem.

1,2&3 are all in 180s.

4 is 50psi before and after HG change. A dash of oil and it rises to 70.

I'm pretty sure it is the rings in that cyl.

To recap again.

I've changed hg and manifold gasket. I've adjusted valve clearances (not 100% sure if I've done that absolutely correctly as stated above)

it now is reluctant to start when hot and seems down on power a bit even taking into consideration the compression problem.

I'm wondering if my valve clearences are a bit tight.

[Gremlin]

Well do them again slightly looser and see what happens?