Mercruiser Alpha 1 Compression test question

Augoose · Mar 24, 2010

Hello,
does anyone know what size adapter needed to run a compression test on a 1989 3.0 Alpha 1?
The only one I have right now reads "M14LR".

Something tells me I'm not lucky enough to already have the right one!

Thanks

Don S · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

The right fitting is usually already made onto the end of the hose because it's the most common. the adapters are made to fit it. So you shouldn't need an adapter at all.

Bondo · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

reads "M14LR".

Ayuh,... If that's Metric, 14mm, Long Reach,..... You're Good to go..
A short 1 would also work...

Augoose · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Excellent. That's the news I was hoping for!
Thanks all

Augoose · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

One other question as well. The boat that I'm checking compression on doesn't run. It has no battery, no distributor, and no coil. Additionally, the owner claims that the original problem he had was burned points and an issue with the starter, but I've got no details other than that. Before I make an offer on the boat, I wanted to check the compression.

So, can I just connect the compression gauge and hand crank the engine? Any recommended way to crank it by hand? I do also have a marine battery that's charged so my other thought was to hook it up and try to get power to the starter just to get it to crank - any thoughts about that?

Bondo · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Ayuh,... You need the Starter cranking, with the plugs out, with the carb open, to do a compression test,...

Period...

Don S · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

If this is a boat you are looking at to buy, even if cheap, RUN AWAY.
Sounds like this guy is wanting someone to haul his junk off his property.

Unless you can crank that engine over by hand as fast as a starter can with a fully charged battery, then you are wasteing your time. Sellers will tell you anything to get your money.

bigskiohio · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

take dons advice unless he gives it to you to check out and run.

Augoose · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

I thought that if you manually turned the engine over by hand, thereby raising and lowering pistons, you'd build pressure in the chamber and could test it. I used this technique on a CJ7 jeep with a I-6 258 I restored (even though I know we're talking boats here, a compression test should be the same), and that technique allowed me to determine that the #2 cylinder was different from all the rest. I know I'm not going to get the same reading as if it was running but I thought this would at least allow me to verify any difference between cylinders.

I'm considering this purchase as a resto project, so I'm certainly not expecting perfection. I'd just like to rule out any major issues with a compression test prior to making an offer.

Thanks all for the input

Don S · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Augoose said:
I thought that if you manually turned the engine over by hand, thereby raising and lowering pistons, you'd build pressure in the chamber and could test it. Is that not right?

No, that is about as wrong as you can get.

Augoose · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Don S said:
No, that is about as wrong as you can get.

Got it. I'll plan on powering up the starter and cranking it that way. Thanks again for the advice.
Great forum!

Don S · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Here is a compression test service bulletin from Mercruiser, it's word for word for the one from Volvo, and both come from GM.

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

Augoose · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Don S said:
Here is a compression test service bulletin from Mercruiser, it's word for word for the one from Volvo, and both come from GM.

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

Thanks Don, great info. That will definitely come in handy. As said above, I'm considering this is as a project boat. I'm certainly not fully knowledgeable when it comes to engines, however I plan on reading and educating myself. I just got done with a 1 year complete frame off resto on a jeep and now I'm looking for a new project. I grew up on a lake and always had boats around, but my paced budget is keeping me in the project boat category rather than to be able to go out and buy something already running.

Thanks again

Don S · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Think about what you are doing then. Buying a boat with a dead engine and outdrive is like buying a boat without an engine and outdrive.
It's going to cost you to get it running, one way or the other. Buy it running or buy used cheap engines and drives. it's all going to come out fairly equal in the end.

cr2k · Mar 24, 2010

Re: Mercruiser Alpha 1 Compression test question

Well you will find no matter what the initial cost, a project boat is going to be like making interest payments. You could buy a nice boat for say $5000 or you can pay as you go on a similar project boat and spend $10,000 over time.

I would also see if I could pull the head and look real close at the wall between 2 and 3 as well as checking the head.

It just kinda SCREAMS at me to run away when the distributor is missing because the points are bad?

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