Compression Readings

[Taz59]

Going looking at a 1997 Four Winns Sundowner 205 & it has a Volvo Penta 5.7Litre Engine,it has done 450 hours.
What should the compression readings be.what else should I look out for


Cheers

 

[Silly Seville]

Re: Compression Readings

A minimum of 120 psi each. 150 is good, 180 and it's had a gentle life. No more than 10% difference between them.

I have to ask...are you doing the testing, or having a technician do it?
There is a procedure involved to get accurate readings. Let us know so we can guide you.

 

[Taz59]

Re: Compression Readings

Just had the report back.

The boat is a five our drive away so I have had a marine Engineer check out the Engine,
the boat has hardily been used this year its 1997 Engine 5.7ltr GLi 450 hours.
Compression readings

1,2,3 150
4,5 125
6 130
7 125
8 140

Engine mounts good
Engine Oil Good
Outdrive Oil Good
Rams Good
Anodes need replacing
Starter Good
Steering Good
Engine Clean
Riser Gasket needs replacing on starboard side
Forward & reverse good
Drive pulley corroided
Oil pressuer 48
Trim Gauge Faulty

any thoughts

Taza

 

[JON NEELEY]

Re: Compression Readings

Well all are easy fixes if your a do it yourselfer. I have a 1996 four winns 225 and absolutley love it. I didnt have a survey done but looked at it twice and test drove. Took it home and started my own maint routine. If the price is right on the boat it seems ok. There is a bit of difference in the compression test tho.
SILLYSEVILLE- what is the proper procedure anyhow?

 

[dypcdiver]

Re: Compression Readings

"Trim Gauge Faulty" most likely the trim sender has a wire with cracked insulation and water ingress into the sender. Be aware that it can only be replaced with the boat out of the water. Not a cheap item, but Volvo Penta seem to think they are expendable like filters and anodes, my boat is 1999 and on its 7th sender. usually only find out it is faulty when I put the boat on its mooring for the season!

 

[Silly Seville]

Re: Compression Readings

SILLY SEVILLE- what is the proper procedure anyhow?

Engine should be cold-24 hours. Remove all spark plugs. Disable fuel system so that raw gasoline is not being introduced to the cylinders. Use a quality thread in style gauge set, not a hand held "rubber tip" style. Disconnect ignition system so that high energy spark is not being passed through the distributor or coil packs. You do not want random sparks in the bilge or against your skin. Open the throttle completely using either the boats throttle control or by manually manipulating the carburetor into WOT position. Use a push button style remote start harness attached to the engine starter to facilitate the direct engagement of the starter. This bypasses any need to use the boats electrical/ignition system. Turn the engine over using the remote starter and allow the engine to build maximum cylinder pressure, which should take at least 3 complete revolutions. Now write down your readings. Remove and inspect the threaded fitting at the end of the gauge hose for oil. If any is present, the oil control rings are suspect. The fitting should be bone dry under normal testing conditions. (This would not be so if introducing oil into the cylinders deliberately to test for bad piston rings.) There should be no more than a 10% difference between the highest and lowest reading on a used engine. 5% on a newer engine.

 

[Maclin]

Re: Compression Readings

Have the throttle wide open also.

 

[Taz59]

Re: Compression Readings

Its 1997 Engine 5.7ltr GLi 450 hours.
Compression readings

1,2,3 =150
4,5 =125
6 =130
7 =125
8 =140

The Engine has only been out once this year and that was just to de-winterise it.
The reading were done by a Marine Survey Engineer.

Thanks for all the replies

Taza