76 Johnson 75HP - Rebuild Problems

[dhym]

We rebuilt our motor last year all the way from the crank bearings up. Oversize pistons and rings etc. Due to piston breakage we replaced the head with a used one. Got it all back together checked compression and like 60lbs each cylandier. Put it on th lake and power barely pulls the boat up. Questions I have is will a head from a different year fit on this engine and will it have a dome capicity therfore dropping the compression? Or are there differnt base gasket thickness that will vary the compression. Any thoughts?

 

[Walker]

Re: 76 Johnson 75HP - Rebuild Problems

Are you sure you have good spark to all cylinders and your carbs are clean? And your link & sync is set up right.

 

[strouds]

Re: 76 Johnson 75HP - Rebuild Problems

shouldent the comp be around 125lb per cyl

 

[Solittle]

Re: 76 Johnson 75HP - Rebuild Problems

60 lbs is not going to cut it. First try a different compression gage to see if the readings are anywhere close. On the heads - some will fit and work well and some won't. Dhadley is the expert on this and you might do a search with an argument of "Dhadley heads" or something like that. I would suspect you have other problems as well (sync & link, carbs, timing). Get the compression fixed first & go from there.

 

[Dhadley]

Re: 76 Johnson 75HP - Rebuild Problems

How many bolts are there in the t-stat cover on the head you used?