Compression test results - 05 M7

[Blk88GT]

I've got about 2100 miles on my M7, 1100 of which are mine.

I fired the sled up for the first time this year last night and it didn't sound quite right.

I did a compression test this morning and got these results. This is a stock M7 @ 700ft elevation.

Mag: 132psi after 3 pulls
PTO: 70psi after 3 pulls, 100psi after 6

Clearly this thing has to come apart. I see some markings on the exhaust side of the pistons and what may be a stuck ring on the PTO side.

Any advice? Should I go through the bottom end as well? Anything else I should do while I'm in here?

 

[ezra]

top end

I would not worry about the crank with olny 2100MI on her I have pulled a few f7 and all have had light scuffing on lower side of jug but not on top side.but I have never pulled one apart that had 2100 on it.all you can do is start pulling off the jugs and see whear you are at.at least the m is a fast top end job.

 

[ripsass]

Unless the top end problem turns out to be from an oiling problem, the bottom is probably fine.

 

[Blk88GT]

I've got it torn right down, crank is going out on Monday to get checked and anything showing signs of wear will be replaced. The PTO cylinder has the nikasil flaked right off, so it'll need a pair of cylinders, pistons rings and gaskets.

Glad I caught it now!

 

[moyiesledhead]

Since you've got it apart anyway, I'd put new crank seals in it too......just because, well...I've been bitten by seal leaks more than once.

 

[Blk88GT]

As soon as the crank comes out, it automatically gets new seals when I do things. No sense going this far and half assing it.

Check out what I found stuck in the reeds on the mag side:

Can anyone tell me where the hell this thing is from? It's plastic?

 

[kane13]

Blk don't know if you have dealt with Recreation Supply in Saskatoon is a great place to get to do the cylinders and get parts from, they had my cylinders done and back to me in a few days, did a great job and it was cheaper for me to send them out there and back to B.C. than it was locally or anywhere in B.C. at the time. I don't think they do it right there but send it just down the road or something and have replacements if needed, great company to deal with.

 

[likkerpig]

May as well do a bigbore? lol!!

 

[ezra]

burn

I 2nd the bb

 

[PCDOC]

http://www.mts.net/~9secgt/Pictures/M7/Rebuild/IMG_3058.jpg[/img]




Looks like an oreo cookie top to me.

 

[kane13]

I third it, might as well you've gone this far...

 

[Blk88GT]

I'd love to do the bigbore, but I want a pull and go sled. I do not want to dick with a boondocker box in my lifetime ever again. The sled needs to figure itself out anywhere from 500ft elevation all the way to 12k without my intervention.

From everything I've read on here and heard from people who own big bores, the only reliable way to get 800 power out of a 700 is a trade in.

 

[Blk88GT]

btw, thanks for the tip on Recreation Supply. I'll be sure to check them out.

 

[blackcloud2k]

Im at a loss on that plastic piece. Does it look the same on both sides? It appears to be melted, is that true?

 

[Blk88GT]

It looks identical on both sides. It's not melted, but looks to have small indentations from bouncing around in the reed cage?

 

[Blk88GT]

After closer inspection, the mag cylinder has the nikasil bubbling off closer to the bottom of the cylinder. What causes this? Not happy....

 

[Blk88GT]

Anyone?

 

[knoba]

M7

BLK88GT thanks again for download,the plastic in your reed cage is it the same type of plastic as the air intake plastic,and nikasil problem,i had a BMW that were prone to softening of the nikasil due to sulfur in the fuel but never heard of that with snowmobiles,just an idea.

 

[Blk88GT]

You're welcome, heopfully you can use it!

Looks like I'm in the market for new cylinders.

 

[007]

Had a friend who was having issues with a 07 m-8 and found the same piece of plastic in his reed cage, just one side.

The only thing that we could think of is the hole that is cut in the intake on the hood.