Polaris ATV Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
231 Posts
Discussion Starter #1
Okay so we're working on a buddy's grizzly 700 just finished putting new head gasket on why we had the head off we noticed pretty bad scoring in the cylinder at the top of the stroke figured we'd put it back together see how it ran and now I want to make sure that the symptoms it has are consistent with lack of compression. it runs good at idle or Full Throttle but cuts off and breaks up in between and sometimes shuts off has oil in the air box which we think is because of the pressurized lower end forcing oil up the Breather tubes, which are into the air box because of snorkels. the bike has been underwater four times and we think the scoring is from sand sitting on top of the piston. just wanted to see your guy's opinion before I advised him to order a new top end kit
 

Attachments

·
Premium Member
Joined
·
4,025 Posts
If the cylinder walls are scored it will definitely effect the compression. If you haven't already, do a compression test. If the rings are leaking it is allowing gasses from the combustion chamber (top side of the piston) into the crankcase. It is probably burning oil too. Even on a new engine a certain amount of blow by is normal. All those gasses have to go somewhere and they get out of the engine via the crankcase vent back into the air cleaner to be burned again. Excessive blow by results in oil being pushed up in to the intake. In Extreme cases the air filter gets oil saturated.

You probably already know that you can't just throw a new set of rings in it. Gonna have to have the cylinder honed at least and probably bored for an oversize piston. Get your cylinder measured first so you know how much oversize you need to go.

Good luck with it!
 

·
Registered
Joined
·
231 Posts
Discussion Starter #3
The top end kid we would buy comes with new cylinder piston and rings. That's pretty much what we were thinking was happening. His whole airbox has 1/2 inch of oil in the it.
 

·
Registered
Joined
·
251 Posts
Many automotive customers would get pissed @ me when I would not take their money to just do a valve job & that it would magnify the worn bore & rings pushing even more compression into the crankcase than before.

They would take it down the street, spend money and return to us later crying.

Glad you caught it & are doing it right. Any job is worth that IMO.
 

·
Registered
Joined
·
231 Posts
Discussion Starter #5
Ya we thought about big bore kits but did not some resrarch and they're apparently a nightmare to tune so we're goin to reuse head and valves and replace whole piston assembly and cylinder. Think that should take care of it
 

·
Registered
Joined
·
165 Posts
If you can modify a spark plug to hook a air line to it , on TDC compression put pressure 100psi . ..listen for bypass, the kill the air , it should hold for a few seconds . ..if not . Then piston, rings,cylinder...
MHO price a big bore kit as well , lol

Sent from my SM-T230NU using Tapatalk
 

·
Premium Member
Joined
·
4,025 Posts
That much oil, you most likely have a problem. Father in Law had a mower that did that. Until he had the engine replaced, he kept a supply of air filters on hand so when one got saturated he could swap it out. You can do the compression test and leak down as described if you want to confirm it before you shell out the cash, but a pretty good bet you will need to rebuild it. Don't forget to replace the valve guide seals...

I have never seen a top end kit that includes the cylinder....Where can you get it from? Definitely save some time. I have always had the cylinder bored and piston fit. Takes longer that way though. Take the cylinder in to have it measured, then order the piston and wait again for them to finish up. Last one I did was only $75 for the machine shop and another $100 or so for top end kit. Included the piston, rings, wrist pin and top end gasket set.
 

·
Premium Member
Joined
·
4,025 Posts
With the decompression system, I think the spec is 50-90, so that's pretty good. It could still be that 90 is as high as it gets too. Gotta figure with the air box full of oil and the scoring you saw, it might be. Only other possibility would be if it's been on it's side or upside down.
 

·
Registered
Joined
·
232 Posts
Have the cylinder bored out to next oversize and put the high compression piston in at same time if you don't mind running 91 oct fuel. Watch some of the chinese parts on ebay. Stick with some of the name brand.

I have a stock bore piston and jug for a 700 grizz with 1100 kms i would let got f0r $200 cdn if interested
 
1 - 10 of 10 Posts
Top