yamaha 115 compression question

[bob johnson]

I was given a 1987 2 stroke 115 hp yamaha motor and I figured Id check the compression and check the spark....thinking it might have had problems...

since it was free!!

anyway the compression was 140 in all 4 cylinders...it is a 2 stroke V4.

but on one cylinder the pressure in the screwed in compression gauge started falling right away . after maybe15 seconds it was less than half of what it started at.

i went back and checked another cylinder....and it didnt fall at all

could that just be function of where the piston stopped when I stopped cranking the motor???


ie and exhaust or intake was exposed??

it has great spark....but the lower unit is missing...and the power tilt and trim is missing.

the motor looks like it has never been worked on..( painted gaskets)

there is a build up of carbon on the piston tops when I look in the cylinders.

is it hard to find lower units for this motor? and t&t units?

thanks

bob

 

[JB]

Re: yamaha 115 compression question

http://www.boatmotors.com/motorparts/

 

[triumphrick]

Re: yamaha 115 compression question

I'm not too sure of your gauge, but of those I have used the pressure has to be released manually. I usually crank for about 4-6 seconds and then read the gauge. All this of course after the motor has warmed up.
One more thing about that motor. Pre 1993 Yamahas had a bad habit of breaking the shift rod. They were steel and would rust in two. You can see the rod running down from the front of the powerhead towards the foot. If not replaced by a stainless rod you can get stuck. Just something to keep in mind before you venture too far.

 

[daraghcummins]

Re: yamaha 115 compression question

Help!


Hello all can anyone help me with the following??
I had to replace 1 cyclinder number 3 in my yamaha v4 2-Stroke 115 1986. It was bought this way as it overheated. All the hard work is done but it wont run??? Spark is ruled out and it is also getting healthy fuel.

Compression.... I have 105 on all other 3 cylinders and 93 PSI on number 3 the one causing all the trouble. This cylinder was running after i replaced the piston and is now not its very od! Dont no what to do with it and the summer is coming. I did not rebore the cylinder just but a standard size back in as no damage was caused to the walls of the cylinder however it did require a hoaning.

Thanks in advance
Daragh - Ireland.

 

[JB]

Re: yamaha 115 compression question

Ahoy, Daragh.

Welcome to iboats.

You need to make a new thread for your problem. Please review "How to get the best results. . ." at the top of this forum and title your thread with the nature of your problem.

 

[daraghcummins]

Re: yamaha 115 compression question

Thank you will do..