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Keep us posted
 

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Check your oil pump drive gear carefully.
 

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Chipped or broken teeth on the drive gear. It was a known problem on the early 650’s
 

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Discussion Starter · #26 · (Edited)
Haven’t had much time to dig in. Ended up having to rebuild the driveline of a Honda Foreman I picked up as a toy. It’s about to be wrapped up. Next project is this one.

I forgot I took some videos of the prowler and the noises it was making. I’m posting them. Unfortunately the audio doesn’t sound right. Like the phone was canceling due to the engine noises.

See or hear anything?




 

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Discussion Starter · #27 ·
I’m pulling the engine. Inspect everything. Might as well. I have the engine stripped and ready to pull it. Looks heavy.

Should I pull the bolts in circle 1 or 2? The ones on the right (2) look like it might be easier and less chance the engine falls through the bottom. Thoughts?
Motor vehicle Automotive tire Bumper Automotive exterior Gas
 

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Discussion Starter · #28 ·
I pulled the bolts labeled 2. Was a back passenger side was a little tough, but, not bad. I decided to keep the engine mounts attached for now to stabilize the engine on the table.

Started disassembly of the motor. The piston had some skirt scoring from slapping against the cylinder. However, play on the crankshaft is beautiful. No perceivable up and down play and barely any side by side. Crank appears fine so far. Will need a new piston, rings, and potentially a cylinder. Will look closer to see if I can get away with re-honing. Or maybe just upgrade for some power. Will wait until all damage is known to see what we are in for.

Found this shaft is very sloppy. Attached a video. This is in the transmission. Bearing looks toast. Metal shavings at bottom of the bearing. Signs of what’s to come I’m afraid.

Will continue tear down this weekend. See what I can see. I don’t have any special tools, so, I might have to get creative to split the cases and remove flywheel.

 

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I’m thinking bevel gear.


No boost, no bottle
Just balls and throttle
 

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Discussion Starter · #30 · (Edited)
I broke down and bought flywheel puller. Should be here tomorrow. That thing is on there. Was hoping to get lucky.

Peeking down through the opening where cylinder removed, not really seeing any damage clearly. But, when I spin the drive shafts, the output shaft that is loose starts to bind real bad. I’m guessing that’s my noise. Bearing is toast. Maybe I caught fast enough to not destroy anything? Doubt it, but maybe.

Any suggested upgrades while I’m in here? Considering the straight bevel gears. But hearing a lot of people complain of noise. Not sure I’ll go there. Thoughts?

And I’m considering things like cam/piston/cylinder upgrades. Since I have to purchase anyway. Since mine is carbureted, I guess it’s just swapping jets to tune.
 

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Discussion Starter · #31 ·
Split the cases. I got lucky. No damage I can find. Just the output shaft bearing. Getting my parts list together. Going to replace all seals and the output shaft bearing.

Next just have to decide what I’m doing with top end and cam.

 

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Nice!!


No boost, no bottle
Just balls and throttle
 

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Discussion Starter · #33 ·
I decided not to replace the piston/cylinder. Just reinstall the top end as is. Not even going to replace the timing chain. I’ll do some riding with what I have then determine how much, if any, more power I need. Anything I do won’t require splitting the cases anyway. Top ends are easy.
 

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Nice diagnostic skills!!!


No boost, no bottle
Just balls and throttle
 

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Discussion Starter · #35 ·
My gut said something with the transmission when I first heard it. Then I read everything about the brake chatter. I wasted a lot of time with that. But, was good to rule out either way. And now I have new back brakes and anti rattle springs.
 

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Discussion Starter · #36 ·
So, I decided to check the piston/cylinder clearances. I bought a bore gauge and decided to learn how to be a machinist with the help of YouTube.

With all my measurements I came up with 0.164mm spacing between the cylinder and piston skirt. I think I measured correctly. Probably will double check tonight and determine repeatability. Looks like stock is 0.045mm. However, I don’t know what the service clearances are (don’t see in manual).

I assume I’m past that. Makes Sense with the damage on piston skirt. This thing needs an overbore. I’ve done 0.5mm over many times. However, I can’t find a piston available in larger than 98mm sizes. No 98.50mm in the usual suspects. Either stock or go to 700 big bore. And to go stock requires replating and honing. Not a cheap process. A simple overbore and hone I can have done for about $100. Piston another $150. Now it looks like $6-$700 to rebuild the top end…..and that’s pretty much stock.

Ugh. Wish these were more popular. Parts are getting hard to find and people want an arm and leg for them.
 

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If you bore 10 over pretty sure you will go through the Nikasil anyway ? Was It smoking?
 

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Discussion Starter · #38 ·
No smoking. I was hearing what I thought was a slight piston slap. Thought it was valve chatter but I readjusted and made no difference. Then chalked up to timing chain since I didn’t have any smoking. Timing chain is fine, so, it was the piston slap I was hearing.

it’s not bad though. Probably going to reassemble to get sure everything else is good to go and think about what I want to do with the top end.
 

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Discussion Starter · #39 ·
Quick follow up. Had a local machine shop I trust verify my measurements real quick. I screwed up mine. He said there is barely any runout. Rings looked fine. He recommended I just green scotch brite the piston and cylinder and send it.

On a side note, he said he’d bore and replate the cylinder for me at a very reasonable cost if I decide to move to a 700.
 

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Discussion Starter · #40 ·
Okay. So got a couple bearings changed out, scotch brite the piston skirt and cylinder. She’s back together. Picking up an oil filter and going to set her back in the frame.

good news. No left over parts after assembly. No binding.

I put the engine together last night. This morning I was concerned I might have put the timing 180 degrees out. So, I popped off the cover to check. I didn’t (don’t think). Then the 4 middle valve cover bolts wouldn’t go in properly. One of them stripped bad. I couldn’t figure out why it was binding.

I put a cobalt bit on my drill And tried to ream out the hole. My bit actually broke. It was struggling.Well, I figured out what happened. There are what look like oil passages down where the bolt passes through. And something in that passage is sliding around and pops into the shaft for the bolt. It’s riding on the shaft that the rocker arms pivot on. I had to use a pick to slide to the side so bolt could go in.

I’m afraid I might have damaged something. The only issue I can see is a click in the valve cover at a specific point in the revolution. However, operates smooth. I might need to replace the rockers. But I’ll wait until engine is mounted in the frame to try and pop off the Allen bolts. They are in there tight
 
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