361 rebuild help needed

[roundhead]

I just put my MS 361 back together after replacing the crankcase. I installed new seals and bearings etc. as mentioned in a previous post, the fit is kinda tight and so the crankshaft doesnt spin too easily. I thought it would loosen up some eventually since I can turn it but it is pretty tight. so I put it all back together and tried to get it to start but nothing. I have fuel, spark, and compression. cylinder, rings, piston all look great. but I have pretty much pulled to exhaustion. I followed the procedure and put everything back together. my only concern is the fit of the crankcase being too tight. is there something I could be overlooking? my thinking is that because of the tightness, the crank cant spin enough to cause compression and fire. I really dont want to tear it apart again so any helpful ideas would be really appreciated

 

[FATGUY]

After assembling the crankcase, did you give the crank a sharp rap with a brass hammer or rubber mallet? I normally tap the flywheel side with the flywheel nut on it. I don't know if this will help you start the saw, but it will make the crank spin freely.

 

[old-cat]

Do you have spark? Is the gap between the ignition coil and flywheel set right? Do you need a Service Manual?
When you put new seals in, it tightens up the crank a LITTLE. IF everything is assembled right you can give it a tiny bit of gas mix in the carb and it WILL fire.
I rebuilt an 026 that had been sitting for several years, so I put gas in the carb and fired it up then it quit, repeat, repeat 3 or four times, then it finally started working perfectly.

 

[Wood Doctor]

Tight Piston Pin Fit?

I may have just run into something similar with an 046 rebuild. The gap on the inside of the piston was too tight to the needle bearing cage, primarily because the shoulders holding the pin were not dead on 90 degrees to the bearing. I used a small mill bastard file and carefully widened the gap's shoulders on the piston so that the piston head would rotate easily with the bearing. This metal is rather soft, so it didn't take much scraping.

After that, all went well. It's rather surprising that the shoulders holding the piston pin do not have to be at a perfect right angle to the needle cage bearing in the crank shaft, and the engine will still purr along. However, I imagine it has to be a rather free fit laterally. Heat could even tighten it up.

 

[adminfti]

This is the correct procedure to reassemble the crankcase
I use it in my own rebuild and it work perfectly!

Installing new bearings in a chainsaw crank case - YouTube

 

[nmurph]

I disagree with Mitch about the order of installation. Where specified, I don't think I have seen a shop manual that said to install the bearings on the crank first. I certainly haven't read every shop manual and I know there is almost always more than one way to cat a skin. I also know that several here do it, but the manuals I have read say to install the bearings in the case first and then install the crank. I find that heating the case in the oven to about 250°F for about 15 minutes and lubing the bearings lightly, and using an appropriately sized socket to seat them, if needed, will slide the bearings right into their pockets. I also chill the crank and lube it, then it usually will slide right on with the case bolts cinching it in place. If the crank is stiff I tap on the clutch and FW nut to relieve the side load. I also use a feeler gauge to measure the gap bw the case and the crank bells prior to disassembly. JMO

 

[adminfti]

I disagree with Mitch about the order of installation. Where specified, I don't think I have seen a shop manual that said to install the bearings on the crank first. I certainly haven't read every shop manual and I know there is almost always more than one way to cat a skin. I also know that several here do it, but the manuals I have read say to install the bearings in the case first and then install the crank. I find that heating the case in the oven to about 250°F for about 15 minutes and lubing the bearings lightly, and using an appropriately sized socket to seat them, if needed, will slide the bearings right into their pockets. I also chill the crank and lube it, then it usually will slide right on with the case bolts cinching it in place. If the crank is stiff I tap on the clutch and FW nut to relieve the side load. I also use a feeler gauge to measure the gap bw the case and the crank bells prior to disassembly. JMO

Its also another way... It's always interesting to read different point of view...