150 miles on a new motor and this

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cliffa said:
As this doesn't seem to be an uncommon occurrence Is it possible that the gudgeon (wrist) pin is slightly too long and thermal expansion is forcing the circlips out of thier groove ?

Cheers,

cliffa.
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The piston will expand more than the pin.
 
Peter R said:
Did anyone ever used this method on a Commando engine ?
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I have Teflon buttons in my T160 but not my Norton yet, but a friend of mine has had some made and uses them on his 920 Norton with no issues that I'm aware of yet.
 
I had nylon buttons in the Pops Yoshimura kit that I installed in my Honda CB550, it ran all day long at very high revs without complaining in the least. No more than a home-made oil cooler (Lincoln power steering cooler) for any relief. Pulled it apart at about 10,000 miles and everything looked just like new, not even piston scuffing. Zero trace of the buttons sliding along the cylinders; they looked like they did the day I picked them up from the machinist.
 
Thanks all for your replies. I will source circlips from Jseng and perhaps the base gasket and Pliobond as well. These Nortons are fussy bitches!
 
Peter R said:
I have seen Teflon buttons as piston pin retainers (although not a Norton engine) the situation we see here in Pete Komarek's engine could have been prevented this way imo.
Did anyone ever used this method on a Commando engine ?

150 miles on a new motor and this
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I tried it in racing but there was a lot of wear. Teflon wears quickly with long linear movement.

GranPaul -I tried Nylon buttons but in a hot Nort they started melting.
 
comnoz said:
And Spirolocks do work but I have never found one that would fit a Norton size groove.
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Yes, the piston needs to be machined for them...And once the piston is cut for the plain round rings ,it probably can't be resized for the spiral locs..But if the piston is machined properly the round rings don't seem to be an issue ..And the pin length must be the correct so it's not going back and forth like a battering ram..Do you guys check the pin length before asembly?
 
bill said:
to use flat circlips you MUST have square machined circlip grooves AND flat ends on the wrist pin. a qualty round circlip with the right wrist pin is fine when properly installed.
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So your assertion is the pistons are machined incorrectly if the wire circlips (included) come astray? Or the pins are incorrect? I have never seen radiused circlip lands.
 
looking at the close up photo of the piston the piston circlip has broken out due to excessive side thrust
if the piston pin is too tight in the small end eye of the conrod it will cause side thrust , if the rods crank and bores are all in line and there is sufficient clearance between piston thrust cheeks and rod small end eye and the rod big end eye has the correct side clearance all should work in harmony without side thrust bieng applied to the clips

i would investigate rod straightness / crank end float & centralisation in cases / small end fit on gudgeon pin / cylinder bore alignment

it is also very easy to rebore a cylinder block off centre if it is not set up correctly on the cylinder boring bar by the machine shop
 
Hillbilly Bike said:
Yes, the piston needs to be machined for them...And once the piston is cut for the plain round rings ,it probably can't be resized for the spiral locs..But if the piston is machined properly the round rings don't seem to be an issue ..And the pin length must be the correct so it's not going back and forth like a battering ram..Do you guys check the pin length before asembly?
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Unless you have alignment problems there is not going to be any side thrust on the pin. A pin has to have some side clearance or on a cold morning the pin will be trapped and the piston will be forced to go oval.
Anywhere from .005 to .025 will work.
 
I had a race Norton engine once that beat up the pin clips.
It turned out that the person who turned the crank clamped it too tight between the centers which caused the crank to bow. Then he ground the throws. Once he released the pressure on the crank it returned to straight but then the journals were crooked.
There was something like .030 difference in the measurement between the small ends at TDC vs BDC.
 
After I pull the pistons off i will check end play TDC vs BTDC. Thanks gents. I was pretty pissed off when this latest bout of problems hit. Haven't touched the bike since August. Thankfully it's better than I feared.
 
Just check the distance between the rod ends with the crank at BDC and then again at TDC. They should be the same distance apart in either position.

Realistically they are seldom perfect. -.005 difference is not uncommon. -.010 is difference is not so good.

This is a fairly common problem when the crank is ground by someone not familiar with these old rubber cranks.

Check it like this.
150 miles on a new motor and this
150 miles on a new motor and this
 
Don't need the caliper on that one.... It's in Braille...I could feel that one in the dark.
Almost a sideways HD.
 
jbruney said:
Don't need the caliper on that one.... It's in Braille...I could feel that one in the dark.
Almost a sideways HD.
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The calipers tell you if things are out of line. I don't think even the most sensitive set of hands will tell you if the two measurements are within 5 thou of difference.
 
I know. Pic is skewed making it look way off. I've been pondering those calipers.. Don't really like calipers for precision stuff, but can't figure a feasible way to utilize an indicator on this application... ponder some more and perhaps have a brain fart because I'm probably going to be in his position within the next two years and need to have my plans organized beforehand.
 
So .010 sounds like a lot. But when you think about it the runout at the journal is going to be magnified about 6 times by the time it gets to the small end and then cut that in half again because you have two rods and you see the runout on the crankpin is actually something well under .001.
At that point your rods big end side clearance is going to be over the runout so not much is going to happen other than slight uneven wear on the rod insert. [again pretty common] But the small end will not be affected.
 
I have a 77 mk3
That had the cases so the cylinder tilted to the right and the head tilted forward .
The machinist found this when he checked the rough surfacing work . He said it looked like the surfacing was done with a blunt rock.
But being a 77 it was most likely built with reject parts under the receivers instructions

Worth checking the cases are machined correctly

Graeme
 
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