Compression testing a bear outboard block

[boostin_7]

Hi all,
My 66 100hp is requiring a rebuild & I'm thinking about using the spare engine block I got from a 67 100hp.
The problem is, I don't know the condition of this block and don't really want to go to all the effort of installing it in the 66 if its low on compression.
Is there any way i can compression test this bare block? Or will I have to try and rig up a starter on it to crank it over for the usual test method.

 

[kodibass]

Re: Compression testing a bear outboard block

if the head gaskets, by-pass/ exhaust/ intake port gaskets are all in-place properly. then I think you could lightly seat the flywheel and do one cylinder at a time leaving the spark plugs out of the other cylinders not being tested to reduce force needed. powerhead would need to be clamped in a large vise, or other means to secure it,. mount the starter and just go black cable from bat-neg to block ground. red cable screw to starter hot post, then just touch other end to bat-pos to crank, or you might be able to use a pull cord wrapped around the fly wheel and pull crank it enuff to get a base line reading. good luck.

 

[F_R]

Re: Compression testing a bear outboard block

Before you go too far, better check closely to see if it is even going to fit up. '67 and '68 have totally different ignition systems. I don't know what if anything was changed to mount that stuff.

Other than that, I agree with kodibass, the hardest part of the compression test would be holding it down so you can crank it. Ropeing it over is good enough, just takes more time and effort because you will only get one or two compression strokes each pull. But not that hard to pull with 3 open cylinders.

 

[boobie]

Re: Compression testing a bear outboard block

I do believe he said he was dealing with '66 and '67 hp mtrs. Not '68. I have taken the CD ignition system off of the '67's and used the'66 ignition system and it worked.

 

[boostin_7]

Re: Compression testing a bear outboard block

Thanks for the advice guys.
I'm going to do some more investigation on the '66 motor to try & find out what's causing the loss of compression in cylinder 4 .
Then try & test the '67 motor.
Do you reckon I'll be able to get gaskets, rings etc for such an old engine?

 

[ajgraz]

Re: Compression testing a bear outboard block

Dunno how your head is held to the leg (bolts? studs and nuts?), but I compression tested a bare Merc block recently by removing the hold-down studs, bolting the powerhead to a board, c-clamping the board to my workbench, and using the starter with a battery and jumper cables.

 

[boostin_7]

Re: Compression testing a bear outboard block

Hmmm .... we tested the '66 engine again & we could only get 30psi readings.. but all were the same.
The guy which tested it for me before was getting 110psi in 3 & 80psi in cylinder 4
Any ideas why the tester read so low? It was a automotive tester though

 

[boobie]

Re: Compression testing a bear outboard block

Try a different tester as they all vary. If the first readings were correct, pull the cyl head on the side that had the 80 psi and take a look.

 

[boostin_7]

Re: Compression testing a bear outboard block

Im keen to pull the head off & have a look, but im waiting to see if the gaskets are available before i do.

 

[boostin_7]

Re: Compression testing a bear outboard block

Ok, I bought a compression tester & tested the engine again.
This time 3 cylinders tested @ 120psi and 1 tested @ 112psi approx, but that wasn't the one which was low before.
I bought some sierra carbon free which I'm going to put through it & see what happens.
I'm going to wait until a day which I know I can take the boat out the following day to give her a good run after the treatment