Bent Crank?? What did I do wrong?

[bama]

I recently put a different crank in a 451 Jonsered that I rebuilt. I put the nut on the clutch side and tapped the crank until I could get the crankcase screws to get a decent bite. Then, I slowly tightened the screws until the crankcase sealed. I don't think I hit the crank very hard at all. I used a 12 oz. ball peen.

When I pull the recoil, I can see the clutch drum move in an oblong fashion. If I put a chain on and lift up the slack, the chain will move about 3/16" up and down when I pull the recoil. I have a new chain, bar, and rim, but the sprocket is used.

I am pretty sure it is the crank that is bent. What did I do wrong? I don't want to do the same thing the next time around.

I plan to use the saw since it cuts well. I would imagine the worst that could happen is the end of the crank could break off due to stress. I would have to do what I already did.

Let me know what I can do better and if any of you run with cranks that are not exactly true. Thanks.

 

[Lawn Masters]

I would think that it woudnt be wise to run it with a crank that is questionable. think about the vibration, and what that could potentially do to the bearings, which could potentially take out the top end, rendering the saw useless entirely.

 

[HiOctane]

Netx time you install a crank,use a propane torch to heat the case in the bearing area to get some expansion.The bearings should then fit easily in the case.

 

[bama]

Netx time you install a crank,use a propane torch to heat the case in the bearing area to get some expansion.The bearings should then fit easily in the case.

Could I get the same effect with freezing the crank?


I have to admit that I am surprised that some tapping could bend the crank. For all the stress that it has to absorb, how can some tapping on the end take it out of round? It pizzes me off that I have to go crankshaft hunting, again!

 

[Mr.]

I've seen someone use an 8oz hammer and ruin a small block crank and I have seen someone use an 8 pound sledge and be fine.

The freezing idea is the ticket. I use it for everything. Just make sure you don't greese the refrigerator.

Fred

 

[timberwolf]

HEat the case and freeze the crank to get the best of both, then do it quick so the case does not cool and the crank warms as little as possible.

 

[bama]

Working on saws is a lot of fun and a stress reliever. However, I sure wish I didn't have to learn some of these assembly techniques the hard way! I will use the freezing/heating when I put a different crank in the saw.


BTW, can you straighten a crank that has been bent? Just curious.

 

[sawinredneck]

BTW, can you straighten a crank that has been bent? Just curious.

I have done it on lawn mowers, my Grandpa built a jig just for it. But I do not recommend it for anything anymore! The new heat treating techniques seem to create a very large weak spot that can become flying shrapnel quickly!!! (Bad things happen!!)
Andy

 

[bama]

I have done it on lawn mowers, my Grandpa built a jig just for it. But I do not recommend it for anything anymore! The new heat treating techniques seem to create a very large weak spot that can become flying shrapnel quickly!!! (Bad things happen!!)
Andy

I kind of figured that would be the case. Oh well.

 

[mikey]

When I was much younger and worked at the Motorcycle shop,we use to true 2 stroke cranks after we rebuilt them.If you have the tool its very simple,but it must be a 3 piece crank.Check with your local bike shop for the 2 stroke race mech.cr's,yz's,etc.He can fix you up.

 

[bama]

When I was much younger and worked at the Motorcycle shop,we use to true 2 stroke cranks after we rebuilt them.If you have the tool its very simple,but it must be a 3 piece crank.Check with your local bike shop for the 2 stroke race mech.cr's,yz's,etc.He can fix you up.

Should any larger motorcycle shop have this setup?

 

[SmokinDodge]

I dont know the price on a used crank in good shape but I know what peace of mind cost. Even is you do manage to get the crank straightened will it be as good as new? Will it hold up to 10,000 rpm when a little tapping will distort it? I don't know. It sounds like you like this saw so why take a chance of making scrap metal out the case with a maybe crank?


Ok, feel free to kick the crap out of me.

 

[mikey]

Yes they should,but you know how that goes.Does your saw have a 3 piece crank?I would think so.Call around to the local bike shops and saw shops.Surely someone replaces rod bearings in 2 strokes.If they do,they have to be able to true the crank after its pressed back together.

 

[JohnL]

could be the clutch only is out of round, try removing it and check the bare crank to see if it has the wobble in it when turning

 

[ShoerFast]

Could I get the same effect with freezing the crank?

This may be a little off-the-farm for some, but it works for me.

Most of the time freezing is the best method, heating the part you want bigger just gives you a little more time to make things fit, but also give you a better chance of fitting parts the wrong way (like bearings a little tilted)

Ovens or Deep fat fryers heated to 350 - 400 degrees should be ok for most metels, but you shouldent heat any plastic or systhect parts.

Luquid Nitregen is the best way to freeze something, a styrafom pail (like a minnow pail) is all you need to haul it a short ways, like say if a local mechane shop had a supply. (it's fairly cheap, a 12 pack of beer can get a pail full on a hot day)

Lot of grocery stores have Dry-Ice, not as cold, but easy to use.

You can keep the dry ice in little cooler wraped in news paper for a few hours, but put it in your freezer to last any lenght of time.
Set up a metel pail, coffee can, what ever will fit the part. Fill the pail with acatone, camp-stove gas, pump gas, anything that will not gel or freeze. Bust the dry-ice up and slowly add the broken chips to the acatone , with the thickest golves you have,,,,, with a thin pair inside of those, watch yourself, it will boil and splatter but keep adding chips of ice till it slows bubbling, that is as cold as it will get.

Coat the part with a little grease, latter you will understand why. Dip the part you want smaller into the slurry, again it will boil up, when the boiling seems to slow, that will be as cold/small as it will get, with your big gloves, and a helper (there usally standing way back if they never seen this before) aling the parts and quickly, but presisely, assimble the parts. If everything is fitting right, you will see the thin layer of frost peel off as the grease keeps the frost from sticking to the part, if the grease/frost peels evenly, things are fitting correctly.

Kevin

 

[bama]

could be the clutch only is out of round, try removing it and check the bare crank to see if it has the wobble in it when turning

I wish it was the clutch, but I can see the movement in the crank end. This is a LEARNING mistake for me.

 

[bama]

I am checking around for bike shops. It is a three piece crank. Thanks Mikey.


Kevin, sounds like a good way to do it. I will have to check for liquid nitrogen. I will probably have more luck with dry ice. When the time comes for reassembly, I will give it a go. thanks

 

[bama]

Found a shop that does all the cranks for the area towns. Less than $10 a piece. I can live with that. I figure that it must work if they do a lot of business. If it didn't and cycles and boat motors were blowing up, they would be out of business.

 

[Madsaw]

If you want I have a a 450 crankcase here. I bought it for parts for my 535. The plastic swapped between the 2. The saw turns over good with no rough spots.
Let me know if you need it just incase.
Bob