Low Compression = Deep Depression

[steviewhitts]

Been having some problems starting the engine on Wizard this winter so while having some work done last week I thought I would have a compression test done.

The readings that came back were 9.5 bar for both cylinders and I'm told the minimum decent compression would be around 20 bar. The engine still starts (eventually) and runs ok.

My question is: is there anything that can be done to improve compression (bigger pistons??) or is it eventually going to be a case of a new engine? The engine is a Volvo 2002 of elderly vintage but I have no idea of hours run so far.

As I only do a couple of hundred hours a year on the engine at most I'm happy to perserve for a while but if it needs replacing I better start saving now.

Steve

 

[ccscott49]

As long as it runs and doesnt burn oil, then I'd persevere. with it, until you have the funds available. But it's maybe going to need a rebore eventually. Not as huge a cost as you may be imagining.
Also you need to find out if its the valves or the rings, before making a decision. Do another compression test, with another compression tester, (always sensible)then squirt a bit of oil in each bore, if the compression pressure rises significantly, then it's bores/rings. If it doesnt, then it may well be valves, which is just a head off job. Then at least you will know what to budget for.

 

[savageseadog]

I'd be very cautious about interpreting compression test readings closely. A lot can depend on the exact configuration of the meter and connection. The fact that both cylinders read the same is reassuring,. It might pay to look at the injection system first.

 

[macnorton]

The test should have been repeated after putting a little oil down the cylinders, if the second result shows less than a 10% increase then cylinders are fine and the problem is valves.
I agree with savagseadog although I would also check valve clearances.

 

[CPD]

ccscott49's advice is absolutely correct imho. dry and wet compression tests will tell you if it is top or bottom of cylinder causing the problem. Either way, I would be very very tempted to do the repairs myself (the end repair may be a workshop job depending upon what you eventually find). It is amazing whaty you will learn, and the skills you will pick up by doing a job like this yourself.

BEFORE you do anything however, do make sure that you dont have any decompressors fitted to the engine that either are stuck open, or are malfunctioning.

Good luck !!

 

[tyce]

very good advice from all here, the wet and dry test will reveal all

 

[oldharry]

Interpreting diesel compression tests is a bit complex, and the result you have may not be indicative of anything other than a poorly set up test set.

A simple test you can do is to check whether the engine is suffering blowby. Block off the crank case breather, and remove the oil filler cap. Place a rag over the oil filler, and hold it down firmly while revving the engine to about 1/3rd throttle for 5 - 8 seconds. Release the rag. If you have a whoosh of air and fumes from the filler then the the pistons or rings are worn. If not, then they are OK, and so basically is the engine.

 

[oldharry]

Interpreting diesel compression tests is a bit complex, and the result you have may not be indicative of anything other than a poorly set up test set.

A simple test you can do is to check whether the engine is suffering blowby. Block off the crank case breather, and remove the oil filler cap. Place a rag over the oil filler, and hold it down firmly while revving the engine to about 1/3rd throttle for 5 - 8 seconds. Release the rag. If you have a whoosh of air and fumes from the filler then the the pistons or rings are worn. If not, then they are OK, and so basically is the engine.

A leakdown test will reveal much more to an experienced mechanic than a compression test. The fact both cylinders came out the same makes the test itself suspect.

 

[oldaljones]

I had a similar problem some years ago with a Volvo 2003 It would only start from cold with easystart turned out to be burnt or pitted exhaust valve seats, Volvo said early engines (mine was 1984) were prone to this and supply hardened valve seats, they quoted me £400 I removed the head and took it to an automotive engineer who replaced all six valve seats for £80
DONT DISPAIR

oldal

 

[nigelhudson]

Don't assume that the bores/rings are shot because the compression is low - the valves are the most likely culprits.

Had the same problem on our 2002 (1986 vintage). Took the cylinder head off and sent it to a specialist. He has stripped it, cleaned it, re-cut the exhaust valve seats (badly pitted but didn't need replacing), re-ground and re-assembled the valves. Cost was £70.

The bores showed very little wear and the oil consumption was low so I'm expecting the engine problems to be cured as a result of the work on the head and last several seasons before any further major work. I hope to finish re-assembling the engine this weekend and restart it. I'll post to let other VP200x owners know the result.

 

[oldharry]

oops - sorry. Seeing double - posting double ... good stuff this malt!

 

[neil_s]

You have plenty of time over which to save. My Bukh engine has been in that state for the past five seasons. Just develop the techniques to help your engine start during the cold patches in the spring, eg, bone up on the manufacturer's cold start procedure, have a can of easistart handy etc. Also, don't let it get worse by letting the engine run without load.



Cheers! Neil

 

[Plomong]

I presume you have been using the correct starting procedure for the Volvo 2002 engine:
1) Turn on ignition key.
2) Pull stop handle fully out and then push fully in again.
3) Turn ignition key to start the motor.

On my previous boat these instructions were buried in an inappropriate part of the manual, were poorly worded, and not referred to nor included in the Starting Instructions section !!!

Some other forumite may enlighten us as to what step 2 does ????

 

[Kylora]

[ QUOTE ]

2) Pull stop handle fully out and then push fully in again.

Some other forumite may enlighten us as to what step 2 does ????

[/ QUOTE ]

On the Volvo MD6A, you need to open the throttle first before pulling out and then returning the stop pull. This action sets the cold start device which injects more diesel than normal.

I would imagine that your engine does the same.

Ash