300 gt food for throught

[rusty bolts]

to bad it has a knock,has only 15 hours on since a $7000 rebuild ,picked it up as a winter project,the owner did not brake it in well at all even has power steering

 

[R.Johnson]

Re: 300 gt food for throught

Make sure that knock is in the powerhead, and not the gearcase before you start taking things apart.

 

[rusty bolts]

Re: 300 gt food for throught

+Funny you should say that.the person I picked it up from said it sounds like it was coming from the bottom of the power head ,He had just picked up the boat and did not want the motors he only wants mercs , he called me to see if I wanted a winter project ,when I started it on the stand I thought was on top , He thought it may be the lower crank bearing ,hard to tell it is very loud out of the water I will check out the lower.Thank you JD

 

[rusty bolts]

Re: 300 gt food for throught

by the way compression is 150 on all holes ,any ideas Jd

 

[R.Johnson]

Re: 300 gt food for throught

It is quite a simple matter to drop the gearcase. I would do that, and see what it sounds like. Your only going to be running it for a brief time, so I would'nt worry about supplying water to it. Just don't let it get to hot. A noise in a gearcase can really telegraph. I had an engine this last summer doing that. It was a damaged pinion, and forward gear. Can you detect any knock rocking the flywheel back, and forth.

 

[rusty bolts]

Re: 300 gt food for throught

No ,it seems to be tight no knock/sound , when i move it back snd fourth with the plugs out .I will take the lower off over this long weekend and see if it has a knock with the lower off thanks JD

 

[Dhadley]

Re: 300 gt food for throught

At 150 lbs compression youre very close, if not at, the point that you need to run high test fuel. It's probably got small bore heads or stock heads cut a bunch.<br /><br />Be careful.........

 

[Dhadley]

Re: 300 gt food for throught

BTW -- what plugs are in it?

 

[rusty bolts]

Re: 300 gt food for throught

Hi NKG z8hs 10 The motor was built by pmc north america,.If i get it going, i will need a boat to bolt it to Thanks JD

 

[Dhadley]

Re: 300 gt food for throught

Thats what I thought.<br /><br />Those plugs are the kiss of death in that motor. So is that compression. Be very very careful........

 

[rusty bolts]

Re: 300 gt food for throught

I myself always run champs,why will that plug make such a diffrance is it way to hot? Is the compression to high ,and may make that motor prone to fail? Are thes motors any good? I was thinking that if i can get it going right i would find a hull for it for fun on the bay Thanks Jd

 

[dafox99]

Re: 300 gt food for throught

Yeah .. I thought those motors ran a low compression ratio (around 7:1?). I was thinking that would equate to a compression of around 90 - 100 psi. 150 psi indicates around 10:1 (or more)?

 

[Dhadley]

Re: 300 gt food for throught

That motor should have numbers around 100 or so. depends a lot on the gauge. anyway, 150 is right where we start to have to run real good fuel. The motor was designed and calibrated for champion plugs. The NGK being slightly hotter is hard on pistons. You can run NGK's but I would richen up the carbs.<br /><br />The V8's are fantastic motors but they have to be set up like a V8 not a V6. Everyone who bad mouths them has had a bad experience with them. In most cases we can trace the problem directly to set up. That includes top rpm, fuel delivery etc.