08 250 HPDI portside middle cyl stuck rings

[87gtNOS]

Found the source of my idle issues!
Middle portside cyl no compression...motor ran fine, boat still went 70 with ease!
Piston is fine, rings are pinched on ex side.
Top piston had same compression as rest but exhibits the same marks and was likely next...
I think it must have overheated at some point before I owned it as it has never idled well for me.
It has 20 over WSM pistons in it.

Boring it 30 over, putting in 6 new WSM pistons.
Shaving a bit off the heads too.
Replacing poppet, and both thermostats. Have not removed tstats yet, hoping to find one stuck.

Had my injectors cleaned and the 3 portside double checked and they were good! However, one from starboard was bad. So I bought a new one from Yamaha.
Vid of my injectors

[javelin90]

Are you not replacing the starboard side rings and pistons with new ones? Are they honing the cylinders?
Would it make it better when breaking in the motor, rings to seat.

[87gtNOS]

Starboard is already 20 over and yes I'm putting new Pistons for all 6

[javelin90]

Was it difficult getting the block dissasembled? Looks like you are on the right track. Do you use a anaerobic sealer for the main block and head assembly?
I hope my vmax will last for many years. I thought it mine fails I'll rebuild it myself

[87gtNOS]

My mistake, whole motor 20 over already. Infact, bores were a little too big...so now it is getting 6 new 30 over pistons instead.

[87gtNOS]

Was it difficult getting the block dissasembled? Looks like you are on the right track. Do you use a anaerobic sealer for the main block and head assembly?
I hope my vmax will last for many years. I thought it mine fails I'll rebuild it myself

It was pretty easy, way more bolts than my snowmobile motor, yamaha apex 4cyl stroke.
I will use loctite 518 on the case halves.
I will spray the head gaskets with permatex copper spray...

[javelin90]

I rebuilt my 03 yukon 5.3L motor last year. Once disassembled/reassembled the concept is same. Were the specs for the bolts, torque yields in a Seloc manual or a yamaha manual? Thinking I might need to get a yamaha book just in case...

[87gtNOS]

I have the service manual on pdf

[javelin90]

87Gtnos message sent

[Tonyc]

87Gtnos I sent you a private message

nice job by the way on the rebuild

[87gtNOS]

Update...long wait for pistons, then only 4 arrived! Hopefully the other 2 on Friday.
Old Tstats seem fine, open nicely as I heat up water, but I put in new ones anyways.

Have the block back on the boat. Just need to plug some stuff in tomorrow night and Friday night install 2 pistons and then Saturday break in!

[javelin90]

Looking good!
message sent

[87gtNOS]

***UPDATE!!

It's running great!
Took it to the dock, tied it up, started right up, a bit of assembly smoke, put it in gear and it idled for 2 hours at 770 rpm. Then took it for a gentle ride for 25 mins, varying rpm, one quick blast to 5200 rpm but most between 3000 and 3500. Went home (5 mins away), did compression test, all cyl's even.
Back out today, ran for 30 or 40 mins, again, cruising speeds...let it cool off for an hour and another 30 or 40 mins back home, felt great, another quick blast to 62mph then let off.

Running great, idles in neutral at almost 1000 rpm and shifts between gears perfectly. No more stalling!! LOL

Will continue to put a few more hours on it gently.

30 over WSM pistons.

[javelin90]

I am glad it is running smoothly..

[87gtNOS]

update, at over 6 hours now, been taking it gently, fouled the new plugs I had in it, cruising at 3000 to 3800....new plugs for the last hour+ (cruising at 4000 to 4900) and they look great. Runs excellent.

Need some 300 heads! LOL

[javelin90]

What manual did you use to get the torque and sequences from?
Thanks

[yam911]

Are you going to be running 91/93 octane? Particularly if the heads have been shaved?

[87gtNOS]

What manual did you use to get the torque and sequences from?
Thanks

I found the manual online for the torque #'s....the whole motor has the sequence written at each bolt, 1,2,3 etc...

[87gtNOS]

Are you going to be running 91/93 octane? Particularly if the heads have been shaved?

I actually always run 91 octane from the gas station. I have bought marina 89 octane once or twice.

As for shaved heads, it seems to be some well kept secret as to what to do!! If it were a Merc, I'd get 100 answers!! Wish someone would just say something like, "check installed squish and cut to make new squish =___"....sorta thing!

[javelin90]

Any luck on getting info for shaved heads.