yamaha 40/50 questions

[wytecraka]

piecing together a bunch of parts ive been collecting to make some stuff run.
got one runnin its an 88 40/50 powerhead 50 carbs/tuner boyseen reeds,
looking to piece together another with the leftover parts.
on to the questions/statements
have a 92 block with an 88 crank and the 92 2 ring pistons, someone in the past had disabled the rev limit and bent a rod, would like to avoid that
have electronics off of a 94 pro 50 and a same from 88 40
which ones are more reliable? not looking to build a race motor, just something reliable.
had the head shaved .025, anyone got an estimate on compression?
stock 50 carbs/tuner on this one as well.
ccm reeds
pro 50 trim
15" mid
nose coned/lwp lower.

recap of my only easy questions
reliability of electronics 88 or 92, if the 88 will even fit on the newer block....
compression? been running 91 non eth in everything as its avail 1/2 mile from my house, will it be fine on 91?
any easy mods ive missed?

probably just run this one until I can piece together a 70 or 90 short shaft.

thanks in advance..

[wytecraka]

also, has anyone used studs for heads instead of bolts? got a crankcase that's perfect except for over half of the head bolt holes have been stripped out by someone over the years. was thinking about using studs and nuts instead so the next time i have to pull the head it doesn't wear out the threads or damage them.

[Fast Fred]

ether black box is reliable , .025 thous is not a lot, maybe 130psi maybe, be fine on 91. you bend a rod when you stick the piston,has nothin to do with the limiter.

[wytecraka]

ether black box is reliable , .025 thous is not a lot, maybe 130psi maybe, be fine on 91. you bend a rod when you stick the piston,has nothin to do with the limiter.

Thanks Fred. Any suggestions on the head studs vs bolts?
Also didn't see any scoring on the cyl with the bent rod. Doubt someone would assemble a block with a bent rod so any thoughts on how that could have seized up?
Thanks again.

[nhpoplin]

Hey Fred. I'm looking to get a 40 head to about 150-155psi for a river running boat. Spend too much time on the river to have a race gas head for every day running. I havent measured the clearance yet as I just got my crank back and dont have it together yet. I was thinking about .075 thous would be a good starting place. Am I on the right track or do i need to get there by welding up the chamber to keep the plug farther from the piston for heat reasons etc? I do make some pretty long river runs. Like 10-15 miles at times and thats a long time for heat to build up

[nhpoplin]

86 yamaha squish band head..could get my hands on an old style head if that would be a better route to go

[Fast Fred]

i would think water bent the rod if the cyl was clean, or they hit somethin. studs or bolts, ether or works, it is common for people to over tighten outboards , make sure your bolts or studs are long enuff, cuzz it is aluminum you need a good amount of thred contact to hold the torque spec.

[Fast Fred]

.075 sounds about right to start, the pocket it self should hold the plug away just fine, just remember you don't want the squish band to dip in on the piston at tdc, or negative squish band, this will choke off the flame front and cause it to knock and she will burn down. ether head works, i like the center fire head my self