787 fast boat update

[irish88]

so today for no real reason i did a compression test it said i had 60psi in one and 20psi in the other i squirt gas down the carrbies and ding dinggg dinggg
sounds a little off like i need to dial in the carbies a bit i mean theres no way this moter would run with compression like that huh?i dose have a hot rod crank and polished crankcase but 60@20 psi???????


i tryed another gage i used the same hose but the other gage said close to the same thing 50@10psi
could i not be seatting the gage right?

 

[Seadoopilot]

does the battery have a full charge ? it needs one to do the compression check
have you had it running ?
Sounds like the rings are stuck at least but the 10/20 is so low that you should get better even without rings
I would pull the head to see what I see
What is the history on the boat ?

 

[seadoosnipe]

Low compression....

An engine will run with low compression. It just won't handle any torque you put on it. With it sitting on the trailer and no back pressure on the impeller, you may get it to run a little. But, that's stretching it. If you do, it won't run in the water, I promise you that.

With the compression your saying you got, the motor is wiped. Sounds like the rings are shot, since you do have some compression. If you have "0", then this is usually from a piston that's melted or has a hole in it from detonation.

I agree with seadoopilot. You've got nothing to lose. Open it up, take a peak. The experience you'll gain is worth it.........:cheers:

 

[irish88]

well its about to start raining here so i got the boat in my shop so tomarow ill pull the head and and post what i see thank you

 

[irish88]

so ive head it run last year i i redid the piston in the back and used a old one for the front after i did that it set for say 6 months mabe longer i come back and this

 

[irish88]

could my comoressison be so low due to never breaking in the moter befor letting it set up??

 

[Seadoopilot]

OK some advice
When ever you re-ring a piston
Take a old ring and snap it in half
Use the old broken ring to clean out the ring groves
The ring should be able to run the grove all the way around the piston without any resistance .
Leaving any carbon buildup in the grove will only lead to the ring seising later .
This leads to loss of compression
I am not saying thats the problem , but you did say you just did them

 

[Seadoopilot]

could my comoressison be so low due to never breaking in the moter befor letting it set up??

No but could be from not winterizing it

 

[irish88]

i dident winterize maan!

 

[irish88]

today!

so i took my head and front jugs ring broke off piston ,bla bla have 3 jugs ready to send to [full bore] for top end rebuild
could be my hotrod crank and connecting rods? are a little worn out to much play where the wrist pin is i don't know it seems like it needsa bigger wrist pin, is there such a thing ?? i would thing they make wrist pins all sizes? anyway i have a stock bottom end that im going to put on top end rebuild ,maybe i should put the stock crank in the ported and polished crankcase now that iam taking things apart and all, that should be ok huh?
also when i took off the jugs , in the port where the rave valve goes it had to ports on the sides has well as the one on top, i have a stock jug ands its just not like this did seadoo make the jugs different?

 

[robin savell lloyd]

so i took my head and front jugs ring broke off piston ,bla bla have 3 jugs ready to send to [full bore] for top end rebuild
could be my hotrod crank and connecting rods? are a little worn out to much play where the wrist pin is i don't know it seems like it needsa bigger wrist pin, is there such a thing ?? i would thing they make wrist pins all sizes? anyway i have a stock bottom end that im going to put on top end rebuild ,maybe i should put the stock crank in the ported and polished crankcase that should be ok huh?
also when i took off the jugs , in the port where the rave valve goes it had to ports on the sides has well as the one on top, i have a stock jug ands its just not like this did seadoo make the jugs different?

Yes this does seem like it is going to be a fast boat. keep up the good work you will get it right. I am sure that there are others here that know way more about this post than I do so I will leave this to the pros.