Pioneer 620 - Won't rev up clean to full throttle

[cdahl383]

Ran up to the hardware store this morning and got some stuff for the flywheel puller. I have this bigger puller that's sturdy but the slots/bolts that came with it are too big for the little bolts that thread into the flywheel. Got some spacers and washers and nuts for the three bolts that go into the flywheel. Now they fit into the puller really well.

Got it set up and sprayed some Kroil on everything to help loosen stuff up a bit. Will try wrenching on it later today. Hopefully it will come off without too much trouble. But I doubt it haha! I made sure to put the nut on the end of the crankshaft too. A buddy of mine forgot to do that once on a dirtbike and attempted to pull the flywheel using a puller and he mushroomed the threads on the end of the crank. Not good!

 

[cbfarmall]

That'll work. Tighten the puller and pick the whole mess up by the puller threads and hit it with a hammer. Ought to pop off.

Presumably, you've grabbed all the available threads with your little bolts. I think one time in 15-20 years I had the threads tear out of the flywheel.

 

[cdahl383]

Got it off! Tightened it up really good and gave it some good whacks with the brass drift and dead blow hammer.

Double checked for air leaks again by doing another pressure test. The clutch side is solid, no leaks. Pressurized and sprayed soapy water all over the seal no bubbles. I won’t be replacing that one. It’s possible someone did that one not too long ago.

Checked the base gasket, head gasket, intake, nothing, all good no bubbles. Can hear hissing from around the case half. Has to be that flywheel side seal.

Next step will be removing the coil/points to get them out of the way and then pull that case half off. That should be fun haha!

 

[cbfarmall]

Almost there. Do enough of these and eventually you can strip one of these saws down in an hour.

 

[cdahl383]

Went out to the garage today on my lunch break and started working on removing the crankcase half. First I took some photos of how the points were oriented. I see there is a mark on there that has to line up with the mark on the case half. Looks pretty straightforward, but I took some photos anyway.

Then I started prying on the case half. At first I used some large flat head screwdrivers in three different spots. Eventually the gap got too big for those, so I moved on to using my pry bars. I just kept tapping on them over and over going around the three spots I had inserted them in. I've got the case half up now where I can wiggle it around a little bit and the threads are almost recessed into the holes. The problem is now the gaps are so big it's hard to fit anything in there to continue lifting it up.

I'm thinking of possibly using my big puller to try and pull it the rest of the way off. I could get a couple long bolts/screws and thread them into where the points are mounted, and then push against the crankshaft end (with the nut on of course) and see if that would lift it up the rest of the way. I'm not sure if that will work that well since there's only two bolt holes to utilize unlike the flywheel which had three. I think I'll give that a shot first and if that doesn't seem to be working, I'll just go back to trying to pry it up gently a little bit at a time. It's coming up, it's just a slow process. I'm sure if I whaled on the thing more I could get it off quicker but I didn't want to break anything.

Here's a few pics of my progress so far...

 

[cbfarmall]

Looks like the flywheel key is still in place. You need to remove that. Then, hold the saw in the air by fan housing and tap the crank with a soft hammer. You have it halfway apart.

 

[cbfarmall]

Basically, you are trying to knock the crank out of the bearing which will stay in the case. Sometimes the bearing stays on the crank.

 

[cdahl383]

I got it apart! Crankcase half removed! It just took a little more prying and tapping to get it off. Nothing broke and I didn't even swear at it haha!

The crank bearing stayed on the crankshaft. Not sure if that will be a problem or not when putting the cases back together. I didn't want to mess with it though until I did a little more research. I got the case halves apart, cleaned up my work bench, and called it a night.

The crankcase appears to have some nasty varnished looking fuel residue in the bottom. It looks like it actually leaked out at some point onto the bottom of the crankcase on the outside. Probably why it was leaking and not holding pressure. I'll have to clean that stuff up. I'm thinking maybe leaving some Chem-dip in there for a few hours might help dissolve that stuff, similar to what I used in the fuel tank. I'll have to clean everything up really good too before I think about reassembling.

I'll knock the seal out tomorrow and after I've cleaned everything up, I'll drive the new seal in. I'm assuming you just drive it in until it's flush with the backside of the case?

The crankshaft and rod seem to be okay. The crank bearing seems okay too, it spins freely, no weird noises or hangups, etc. Didn't feel any play that I could tell.

I had to remove both keys like you said to get everything off. The smaller one closer to the crankcase is for the points. The larger key further out on the crank is for the flywheel. Got them out without too much trouble.

I didn't notice a gasket anywhere. I swear in the parts diagram I have it shows a gasket there. I've had several folks tell me there's no gasket though, so I guess I'll just use some sort of fuel resistant sealant/gasket maker and call it a day. Any suggestions on that? Maybe Yamabond or something similar?

I was just glad I got it apart tonight. I knew once I got it further up and I was able to wiggle it around it was just a matter of time before it came off. Thanks for the help and tips!

Here's a few pics...

You can see in the pics where the old fuel/oil must have sat for a VERY long time and turned to varnish.