M8 Top End

fokus2k3 · May 17, 2015

Hi guys,

I have a 2007 M8 and one cylinder is 10 psi lower than the other (120ish psi vs 110 psi). Does this justify the need for a new top end, or do the rings just need changed? The sled has around 1800 miles, I'm not sure if the previous owner ever changed the top end.

Thanks

tundramonkey · May 17, 2015

With that many miles on the top end and a 9% difference between the cylinders I would replace the rings, pistons, wrist pins and bearings. I would also have the cylinders checked out just to make sure they are good.

ezra · May 17, 2015

I would slap a full top end on it.
I have had good luck with spi . done quit a few lay down twins with them.

Hardass · May 17, 2015

Thats not really that many miles for a m8. Did you check it more than once and with a different tester? i would before you change any thing. Did you check by pulling one plug out of both cylinder and holding the throttle wide open and five solid pulls on each cylinder?

fokus2k3 · May 18, 2015

Hardass said:
Thats not really that many miles for a m8. Did you check it more than once and with a different tester? i would before you change any thing. Did you check by pulling one plug out of both cylinder and holding the throttle wide open and five solid pulls on each cylinder?

Only checked it with one tester back when I bought it, I rode it 3 times and with summer I'm looking into the cause of it now. I don't recall us ever holding the throttle wide open, we did pull it about 5 times per cylinder.

It wouldn't be bad to have a compression tester of my own laying around, I'll probably snag one up.

Hardass · May 18, 2015

Yes have One plug out of each cylinder and hold wide open and try it again. 4 or5000 miles on these motors is not uncommon at all. Good luck.

kiliki · May 18, 2015

Hardass said:
Yes have One plug out of each cylinder and hold wide open and try it again. 4 or5000 miles on these motors is not uncommon at all. Good luck.

^^^^^ what he said a non ho m8 we don't even open them until 4k.
make sure you run the motor until warm before you test it, everything has to expand to normal operating temp.

ezra · May 18, 2015

we are under the assumption he bought it from a stand up guy.
but yeah U usually wont crack them open till 3500 or so. unless I was in your situation.

fokus2k3 · May 20, 2015

Thanks for the response guys. I rented a compression tester today, and doing it as you said to, I have 1 cylinder at approx. 115 psi and the other at approx 110.

kiliki · May 20, 2015

if its more than 10% on a warmed up motor then yes do a top end. if it runs good and under 10% ride the guts out of it!!! it is a M8 not a D8.

Phizzer · May 21, 2015

fokus2k3 said:
Thanks for the response guys. I rented a compression tester today, and doing it as you said to, I have 1 cylinder at approx. 115 psi and the other at approx 110.

115 and 110 is not bad at all. Your still within 5% of each other. Spend your money on something else this year!! SLP pipe and can combo??

fokus2k3 · May 21, 2015

Awesome! It has a speedwerx set up on it, I'd prefer the slp set up but no need to spend extra money for one.

Hardass · May 21, 2015

Speedwerk pipe is a good one keep it

BD-Xtreme · Sep 2, 2015

m8 piston option

Here is another option for replacement pistons. We have a lot of brand new take out pistons from when we do big bore kits to new snowmobiles.

This is the HO style piston, but will still work just fine in the 2007--2009 motors too.

http://www.bd-xtreme.com/index.php?id_product=67&controller=product

mountaincat 800 · Sep 2, 2015

BD-Xtreme said:
Here is another option for replacement pistons. We have a lot of brand new take out pistons from when we do big bore kits to new snowmobiles.

This is the HO style piston, but will still work just fine in the 2007--2009 motors too.

http://www.bd-xtreme.com/index.php?id_product=67&controller=product

A reasonable person would think that after making profit on all the big bore kits that you sold and the number of free to you take off pistons that you have. Why wouldn't you offer an even better price than $95.00? To me this just shows how greedy of a company BDX must be. I could be wrong. Perhaps you discounted the big bores $95.00 to keep the pistons.

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M8 Top End

fokus2k3

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tundramonkey

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ezra

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Hardass

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fokus2k3

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Hardass

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kiliki

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ezra

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fokus2k3

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kiliki

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Phizzer

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fokus2k3

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Hardass

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