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Discussion Starter #1 (Edited)
Replaced the crankshaft and now it won't hand crank with the plugs in. Turns over smooth w/o the plugs. With the plugs in, it turns over for on rev but can't get the second cyl. to turn over without breaking the rope. Stock crank (stroke is good) factory gaskets, same stock pistons but somehow the compression is got to be way high. I've run out of ideas and don't want to start tearing it down without knowing what I'm looking for. 35 years of teaching mechanics but first sled eng. 01 Polaris 800 RMK.
Thanks for any suggestions, Moze
 

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Discussion Starter #5
Did you run a compression test on it? Those early 800's were hard to pull, but not that hard...
Compression gage isn't holding but I did see 200 on just on crank over. Bk calls for 140 lb.
 

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Sounds like something wasn't put together right. As Dan said those were hold to start but nowhere near like you are talking about.
 

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Discussion Starter #7
Sounds like something wasn't put together right. As Dan said those were hold to start but nowhere near like you are talking about.
Best that I can measure, the stroke on on the money. Dealer swears that the crank is stock. Used the same pistons that it had. The old crank was broke and the rig had low mileage so I simply replaced the crank. Used new gsks and seals. Maybe the rod length is wrong. Comments?
 

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Possibly, could be the pistons are hanging up as well. Anytime I do work like that on friends I always replace at least the piston rings and hone out the cylinders just to be safe. And if the price is right and time isn't important then a full piston kit and if the cylinders need to be go bigger I send them to indy specialities with the pistons and cylinders/rings and they match them up perfect so the fit is awesome. Personally I would at least pull the cylinder head and have a look around and maybe even pull the cylinders and make sure nothing is caught. Could be something just got caught, just hope you didn't scratch the walls.
 

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Discussion Starter #9
Possibly, could be the pistons are hanging up as well. Anytime I do work like that on friends I always replace at least the piston rings and hone out the cylinders just to be safe. And if the price is right and time isn't important then a full piston kit and if the cylinders need to be go bigger I send them to indy specialities with the pistons and cylinders/rings and they match them up perfect so the fit is awesome. Personally I would at least pull the cylinder head and have a look around and maybe even pull the cylinders and make sure nothing is caught. Could be something just got caught, just hope you didn't scratch the walls.
Thank you. I did deglaze the cyl. walls. It's a twin cyl. and unlikely that both pistons are hung up. The best that I can come up with is that the rod is longer. Stroke would be the same except that the piston would come up higher increasing the compression resulting in my 200 lbs. This would be due to the lesser head space. Guess I'll pull the head and cyl and look around. Not a lot of options here. I wasn't aware that the old crank could be repaired. Cheaper and I wouldn't be thinking about rod length. Damn, I don't want to pull that eng. again. To make matters worse, I'm doing this for a friend. Ha!
 

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I would do it with the engine in the sled if you are just pulling cylinders and the cylinder head. You go to change that crank or rods then yeah you end up pulling it. It is still possible the piston rings are hanging up. I've had it happen to me even with all new stuff when I wasn't sending stuff to indy specialities.

Yeah gotta love working on other peoples stuff sometimes!
 

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Discussion Starter #11
I would do it with the engine in the sled if you are just pulling cylinders and the cylinder head. You go to change that crank or rods then yeah you end up pulling it. It is still possible the piston rings are hanging up. I've had it happen to me even with all new stuff when I wasn't sending stuff to indy specialities.

Yeah gotta love working on other peoples stuff sometimes!
I wouldn't exclude anything at this point however, why the 200 lbs compression. I'll start with the eng. in the sled. Thanks a lot for your input.
 

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I'm thinking the same as you. If the compression is 200+, that would seem to point to connecting rods that are too long, especially if everything else is the same. Maybe you can double up on the base gaskets to relieve the compression issue, but that will change the intake/exhaust port timing...

I had an 800 with 150 psi, that thing was a bear to pull. I can't even imagine 200. Gads!

Have you checked the squish? That could be telling...

 

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Yeah didn't think about the "squish" part of it. I think as well it might be rods but hopefully it is just one of those simple fixes we all hope to have happen when we work on our sleds or anyone else's
 

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Discussion Starter #14
I'm thinking the same as you. If the compression is 200+, that would seem to point to connecting rods that are too long, especially if everything else is the same. Maybe you can double up on the base gaskets to relieve the compression issue, but that will change the intake/exhaust port timing...

I had an 800 with 150 psi, that thing was a bear to pull. I can't even imagine 200. Gads!

Have you checked the squish? That could be telling...

Thanks you for that. Never heard the term before. Know what they are talking about but not the term. Will do.
 

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To measure your squish
Take a piece of soft solider (50/50 works)
Make a bend in it so that when you put in the spark plug hole it will go all the way to the outer wall.
Put the solider directly above the wrist pin and slowly rotate the engine over to squish it!
Do both sides of each piston.
Solider is 0.125 (1/8") most squish bands are about .060
 

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Discussion Starter #18
Head thickness is 1.107. Anyone have a spec for std head thickness? 2001 polaris 800 RMK
 
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