NWP shortblock ms 390 shearing flywheel key

[taxidermist]

I installed a nwp 390 in a ms 310 case. I went to start start it and it bucked, it never did start. I took the flywheel off and the key was sheared. I thought it might have been cracked from when the ms 310 seized and i just missed. I replaced it with a new OEM flywheel and got it to start. It did not run good so I started to adjust the carb and after a few restarts the key sheared again.

I do small eng repair and have rebuilt about 30 saws so its not my first rodeo lol Just never used a nwp short block before and was wondering if anyone has had any issued with them.

I do have a call into Bayleys to see if they have had any issues.

Thank you,
Rob

 

[nmurph]

How are you tightening the FW nut? If it's with an impact, make sure you have the nut snugged against the FW bf you hit it with the gun. Not having it tight has cost me a couple of FW keys (sheared one a couple of weeks ago bc I got in a hurry). Snugging them down and then hitting them with the impact will work without a problem...I've done hundreds this way.

 

[old-cat]

I don't mean to belittle you. Make sure the taper in the flywheel and crank match plus no burrs etc. Also make sure you have the right torque on the nut, 28 Nm

 

[albert]

You don't need the key, even if cast in. De-bur the flywheel. Clean shaft and bore with solvent, it must be oil free. Mark the shaft and flywheel to line it up, tap the flywheel on with a deep socket so it doesn't slip and torque it. Most shear from not being tight enough like Murph said.

 

[taxidermist]

Thank you for the replys. I can say that I have never used a impact wrench to tighten or remove any flywheel. I use rope in the jug and a ratchet wrench.

As for the torque wrench I can honestly say I have never used one on any flywheels.

I will clean up the shaft in the am and try to torque it down and see what happens.

Thank you,
Rob

 

[fearofpavement]

I always use a butterfly impact to remove clutch and flywheel nuts. Don't need a rope in the cylinder. In fact, you don't even have to have a spark plug installed and it will work equally well. It's fast and effective.

 

[firefighterwolf]

The others are spot-on as far as what to check first. However, since you are applying significant force with a ratchet and that it has sheared a flywheel twice... I'd bet a dollar there's a timing issue with the new shortblock.

 

[nstueve]

Yea what they said. Also is your ignition module tight? If it gets a little to close it could hit the flywheel magnet and sheer the key. The tapered shaft allows no key to be used as long as alignment is good.

 

[a. palmer jr.]

Since it has the key sheared you can try turning the flywheel about 1/4" clockwise on the crank, measured at the outside perimeter of the flywheel, this will in effect retard the timing a bit if you think maybe it's timed too advanced. If it runs too lazy then you can always set the timing the way it was.

 

[texastele]

I put the motor in an ms310 and it sheared the flywheel key on the old flywheel. I put on another flywheel from a part saw and I haven't had any problems.

 

[taxidermist]

I installed the flywheel again and torque it down to 28nm and it fired right up. I was planning on using it this weekend but we have had 2 days of cold temps and blowing snow. Maybe I will be able to hit the wood pile in thew AM and try it out.

Rob

 

[a. palmer jr.]

Bad weather here too, won't be doing anything with chainsaws but I have plenty to do, Christmas shopping, taxes, insurance to worry about this time every year.

 

[sachsmo]

Don't do Stihls,

so the 290/310/390 have the key cast into the flywheel?

Had a Husky 2100 that would shear keys, I lapped the flywheel to the tapered snout with fine clover valve compound.

No more sheared keys on that one

 

[nmurph]

Most modern saws have cast keys.

 

[HuskStihl]

Before I learned on here that you don't need a key, I sheared one, used a triangular file to make a groove in the flywheel where the old key was, made a new "key", glued it into the groove and reassembled. Prolly just needed to torque it back down

 

[a. palmer jr.]

Don't do Stihls,

so the 290/310/390 have the key cast into the flywheel?

Had a Husky 2100 that would shear keys, I lapped the flywheel to the tapered snout with fine clover valve compound.

No more sheared keys on that one

What would you do if, when it sheared the key it took part of the crankshaft with it? I have an old saw that tore about 1/8 of the crankshaft away when it sheared. I left the key out and used red loctite on it, then tightened the nut about as much as I thought it would take. Haven't run it since then but wondering if it'll hold.. This old saw isn't worth putting another crankshaft in it.

 

[sachsmo]

Red is pretty tough, I think the green 'retaining' compound is good stuff too.

 

[a. palmer jr.]

I think it's supposed to warm up later this week, I have a few saws that I've rebuilt that I'll fuel up and see if they're any good.

 

[taxidermist]

Well here is a update! I used the saw all weekend and it never missed a beat! I will always use a torque wrench from now on.

Thank you for your help.
Rob

 

[sefh3]

Make sure your crankshaft is clean of no oils or grease. It will sheer a key in a second.