Compression Test?

[adluginb]

First off thanks for any advice. Second I know nothing about engines what-so-ever other than how to change the oil.

Ok... I bought a used boat without testing it, I know its my fault but seller assured me nothing wrong, so much for trusting people. It is a 98 Larson that appeared to be in perfect shape and atually is in perfect exterior condition. Took it to the lake and the boat will not plane. Only bogs down and eventually dies. Haven't been able to get boat into volvo mechanic yet since they are so busy but had a buddy look at it and he did a compression check? The Engine is a 3.0l Volvo which I guess is a chevy. #1 = 150, #2 = 0, #3 = 0 and number 4 cylinder was 110. My friend informed me that I needed a new engine....Great!!! so much for boating this year.

Can you guys tell me what could be going on from this info?


Thanks

 

[Maclin]

Re: Compression Test?

Usually the next thing to do is a leakdown test to see if it is valves or rings, but with zero on 2 cylinders and assuming the compression check was done corrrectly then it is time to remove the head.

It could just be a valve problem but the root cause is probably something more serious. If the head gasket blew out then it could be because the head warped due to a serious overheat. The same type of overheat can get to the valves also. It could have holes in the pistons from running too lean and detonating. Lots of things can be on the list until you remove the head and go from there.

 

[Maclin]

Re: Compression Test?

You might also post all of the recent history that you know of. Like when it was run last before you got it, was it in use a lot by the previous owner or ???. Last known impeller change. Things like that

 

[adluginb]

Re: Compression Test?

Thanks I ordered a new impeller to change since didnt know when it had been done. Will start pulling the head off this week. Hopefully just need new gasket. Anyone know what a head costs? Volva penta 3.0l or chevy 181 long block?

Do you think I should do the leak down test before taking head off?

Thanks

 

[Maclin]

Re: Compression Test?

With 0 compression on 2 cylinders there is no point to the leakdown test. Something is just wrong and in every scenario I can think of the head has to come off to figure out what it is.

 

[Boatist]

Re: Compression Test?

I agree with 0 on two clinders hope it is a head gasket. Leak down test will not help if you are starting with 0 how is it going to leak down.
It could also be a cracked block because it was not winterized and froze up.

Wish you the best of Luck.

 

[mtnrat]

Re: Compression Test?

Worst case scenario, you will want a new long block. Just google marine long block 3.0 and you can get an idea of what is available. Looks to be about $1800 to $2200. Swapping engines is usually easy and you will easily salvage the season. I do hope it is an easier fix than that. I would look up how to do a compression test and see if you get the same results.

 

[Robj]

Re: Compression Test?

With 0 on two holes, my guess it is tulipped valves. A blown head gasket would still show a small amout of compression. You should not have to replace the head, just take it to a machine shop and they will make it as good as new for a couple hundred $$.

The other possibility is a hole in the piston, in which case you need a new motor. Hopefully this is not the case.

Have a great day,

Rob

 

[Maclin]

Re: Compression Test?

With 0 on two holes, my guess it is tulipped valves. A blown head gasket would still show a small amout of compression. You should not have to replace the head, just take it to a machine shop and they will make it as good as new for a couple hundred $$.

I agree with Rob, this is what I would expect (and hope for if it was mine!). The head may even be warped some but the machine shop can usually reface the deck, hopefully no cracks from an overheat.

If it is the head (tulipped valves, or warpage, etc.) then the machine shop will probably be able to tell you if they think it was from running too hot or whatever they think from what they find. If it was from an overheat then you need to make darn sure the cooling system does not have a lingering problem that can start this cycle all over again.

 

[Maclin]

Re: Compression Test?

I am kind of hesitant to post this and pile it on, but there are several other key items that may not have been taken care of. The drive bellows would be the next thing on my list. If that is old (3-5 years) and leaking then water will enter the boat and on the way in will splash or even drown the ujoints and yokes and rust can start, also this water can enter the drive thru the upper unit where the driveshaft yoke goes into the drive and dilute the drive fluid eventually causing damage internally.

I am not sure what all you checked or had checked before you put it in the water, but while it is down is a good time to check some simple things. Check the drive oil level and also the oil itself to see if it is milky or cloudy (water contamination). Maybe just go ahead and change it.

Hopefully you have an owner's manual, if not you can get one in PDF format from the Volvo Penta site. It will have these key items spelled out.

Good luck!