[adkrider]

I guess its to be expected but gosh its been a tough introduction to snowmobiles. 3800 miles has been running great all season had it on the lake heard a loud high pitched scream from the engine, shut it down. Compression tests yield 120 MAG and 25 PTO. It still runs no knocking but very little power. Could not get a good look at the piston but I assume its cracked or has a hole in it. The plug was grey indicating pre-ignition or lean condition. Since its efi, not sure what could have triggered this. Plug chops from yesterday and every time before look perfect and if anything the 700 efi motor runs rich from the factory.

So what do I have for rebuild/replacement options? Can I drop in a ZR 700 engine and use the Fuel injection/stator/ignition/pipes from my wildcat engine? What other engines will bolt up to the bellypan of a 93-95 wildcat efi? Im just brainstorming here and trying to reach the best resolution. I know I could likely re-do the top end but thats more of a summer thing when I have some down time. I'd like to get it up and running for some events later this winter. ARRRGG!!

 

[mr.deeds]

A new top end isn't a summer thing.... it's a couple hours on a weekend. It really is easy,,, a ton easier than dropping a new engine in. I would check it out and if all it needs is some new pistons-- just buy them and slap them in. The first time i rebuilt one i just did a little research and it worked fine.

 

[BC_Dan]

The hard part is figuring out what caused the lean condition. With the damage on the PTO side, the crankcase seal is usually the culprit.

 

[RJ Gleason]

It would most likely be either the PTO crank seal, or the throttle body mounting flange (rubber part). Since these engines use a cover plate on that seal, you can change it without splitting the case.

I would replace both as a matter of course after replacing that piston.

 

[kccats]

Yep likey a seal! Gotta pull it down and see? Yes a ZR 700 will drop right in! Gotta use the flywheel and stator off the EFI!

 

[adkrider]

What should I be using for pistons? OEM? Whats the most reliable?

Thanks for the help. I assume when I go in there I should obviously check the crank and rods looking for heat discoloration, etc. Anything else to check while Im in there?

 

[RJ Gleason]

Where you located?
I have a cyl, head, and piston from a 700.

 

[BC_Dan]

Flush out the bearings of the crank, there could be some debris from the piston that made it down into the bearing. Look for scoring and wear where the crank sits. There's not much down in the bottom end, it's pretty easy to look for bad spots.

 

[adkrider]

Where you located?
I have a cyl, head, and piston from a 700.

Im in Saranac Lake, NY. Its about 3 hours north of Albany and 4 hours east of Rochester.

I think I found the culprit. There are 10-15 pins that hold the rubber intake boot onto airbox and 3-4 near the PTO side pulled out over the course of my last ride and are now missing, would this cause my airleak?

As for the rebuild, I have a shop manual so I'll start there, but I am assume its something like this:
Drain coolant
remove exhaust, intake accessories
Remove cylinder heads (I'll do both pistons while Im in there)
Remove piston pins and pistons
Inspect crank for wear or loose bearings
Inspect cylinders and heads for wear / pitting
Hone cylinders (can I purchase a fitting for my power drill and do this?)
Install new pistons and rings
Install cylinder heads and torque to correct specs

 

[RJ Gleason]

That is a good list.

The parts are available if you want them, $100 for the bunch, you pick up.