compression saab900 - cernay12
we\'ve just bought a \'98 saab 900s bifuel (petrol/lpg saab installed) at what seems like a pretty good price @£2500. It has done about 110,000 miles . The gas was not working when we bought it but the vendors said it was a fairly cheap repair.

After conventional service the car was running nicely and after the gas supply specialist service the gas was kicking in and the repair was not too expensive. But the gas specialists said that the compression on one cylinder (the first) was down and this affected performance and the tickover in particular.

In fact it is \'lumpy\', compared to our 9000 but the car seems to run pretty well and does not burn oil or water and temperature seems stable. The performance on gas is similar to petrol.

What are the implications of this compression variation in your view? Do we need to worry? Is there anything we can do short of dismantling the engine?

Do we need to? Is there anything to check which may affect the compression in this cylinder?

I\'d be grateful for your response if you can

compression saab900 - Mike H
Try posting your question here, as although general principles can be applied this is Saab-specific:

Personally, my view is if the compressions is down you have a potential problem that needs fixing - how long you leave it is up to you!
compression saab900 - cernay12
sounds worrying. thanks for the site. I will try it
compression saab900 - Pete F
Compressions are often low because of valve leakage. Don't know the valve operating design on this engine but are the valve clearances OK assuming no hydraulic tappets?
compression saab900 - cernay12
thanks for your reply but I don't really know answer to your question and will try and find out
compression saab900 - Aprilia
At that mileage, running on gas, it is highly likely that you are suffering valve seat recession. This is a particular problem with LPG and some head designs are much less tolerant than others - I don't know specifically about SAABs. LPG is very 'hard' on the valves.

The cure will likely be a head overhaul - new valves and seats.
compression saab900 - cernay12
much obliged for reply. Head overhaul sounds expensive - is it? Can any garage do it or is it a dealer only thing? Forgive banal questions. Is there somewhere I could look to find out more?
compression saab900 - Aprilia
First of all get a proper compression test done - wet/dry, cylinder leakdown.

If it needs new valves and seats it shouldn't be too expensive - a good garage or a SAAB independent would be able to do it without much trouble. You would probably need new valves and seats - I'm not current with SAAB parts prices, but shouldn't be too dear so long as you stay away from the franchised dealer for the labour.

Value my car