OS 21xm v1 question

[Lowell Tryon]

Not sure if anyone saw the 21xm for sale on rcgroups, but I bought it knowing beforehand the seller said it was hard to turn over by hand.
I got it today- def. hard to turn over by hand, I’ve had some new KB’s that were hard, but not so hard I was afraid to keep pushing it.

Does this seem normal? It’s missing the shim, but that shouldn’t matter?

 

[topfuel443]

Have you torn it apart to check out the internals? Most folks do remove the head shim, but you should always check the head clearance to make sure nothing hits. Is it hard to turn over through the whole rotation, or just when the piston gets near the top of the stroke?

 

[Grimracer]

when you say tight.. do you mean all the way around the stroke or just at the top.

Grim

 

[Lowell Tryon]

I took the head off and removed the sleeve, everything seems to be ok, no discoloration or wear marks. Only gets tight at the top of the stroke.

 

[Grimracer]

cool.. RUN IT!

Grim

 

[Lowell Tryon]

this is the spot where it gets stuck and I can’t push any further(without putting in a vice or something crazy). Is the chipped cooling fin a sign of something bad like overheating?

 

[Lowell Tryon]

Cranked it over with a socket wrench, assuming the starter can turn it, I think it’s ok...

 

[Mike Hughes]

That thing looks like it has not been run. Not hitting from lack of shim. Tight at the top is the way they come from factory. They need to be broken in. Thats the fun part. Good luck.
Mike

 

[Mike Starrett]

this is the spot where it gets stuck and I can’t push any further(without putting in a vice or something crazy). Is the chipped cooling fin a sign of something bad like overheating?

That looks waaaay down in the cylinder to be that tight on an OS. If it's been run...I would look for another problem other than not broken in.
I see your in Louisville. I'm in Georgetown, In and have a bunch of parts we could use to sort out the problem. Hopefully it's just super tight.

 

[Lowell Tryon]

That looks waaaay down in the cylinder to be that tight on an OS. If it's been run...I would look for another problem other than not broken in.
I see your in Louisville. I'm in Georgetown, In and have a bunch of parts we could use to sort out the problem. Hopefully it's just super tight.

Nice to see someone else around here still messes with these! Yeah, the crankcase definitely looks like it has been run, chipped fin and small nicks and scratches. But there is no sign of nitro fuel inside, doesn’t smell like fuel at all. Very confusing. Could this problem occur if someone were to swap in a new sleeve and keep the old piston?

 

[topfuel443]

Mike Starrett is right, that is very far down in the stroke for an OS to be tight. I would do som emore investigating before trying to run it. The piston on the OS is almost flush with the top of the sleeve at TDC. It could be someone mix matching parts like you mentioned.

 

[Mike Starrett]

Nice to see someone else around here still messes with these! Yeah, the crankcase definitely looks like it has been run, chipped fin and small nicks and scratches. But there is no sign of nitro fuel inside, doesn’t smell like fuel at all. Very confusing. Could this problem occur if someone were to swap in a new sleeve and keep the old piston?

It could be caused by a number of things. I'd have to see it and maybe swap a couple parts (temporarily ) just to see if the problem changes. That chipped fin concerns me?

 

[Lowell Tryon]

There is probably some very slight variance in the dimension, but can anyone measure the diameter of the sleeve top and piston?

 

[Mike Starrett]

Measure your liner and see if it's round. Can you push the piston higher into the liner with those parts out of the case?

 

[Lowell Tryon]

piston diameter is 16.6mm. sleeve diameter at top is 16.5mm. Also, what is this mod in the pic? Trying to make a bit more space in the crankcase?

 

[Mike Starrett]

I checked some I have (well worn) and they were all about 16.57 at the top of the sleeve and about the same piston dia. As I said they are all used and some fits were different than others. A couple of the used sleeves may have been squeezed too.

 

[camaroboy383]

I'm surprised nobody has brought to your attention the fact that the sleeve may have been pinched... and if it has, probably went to far... get a piston and liner and run it... unless you can lap the piston back in... but sounds like it's gone beyond lapping back in...

Just sayin,
Ac

 

[camaroboy383]

My guess on the backing plate cuts would be to make room for the transfers.. seems some one was grasping at straws...

Ac

 

[Lowell Tryon]

Yep, it’s seeming like this may have been a bit of a lemon... oh well, it’s risky buying these used. Maybe this lower will be a good candidate for brushless.