Crank Rebuild Problems
Posted: Thu Jul 11, 2019 10:56 pm
I'm continuing with my 53 model 18 rebuild and have some more questions if someone can help. It's a bit long winded I'm afraid.
I stripped it due to lots of bad noises after a run, at first I thought piston slap and sure enough about 0.5mm. However then took the barrel off and found I also had about 0.5mm lift on the conrod so the bigend was goosed too.
Split the crank and found the pin, rollers and conrod bearing surface all in a bad way.
Bit the bullet and ordered a new crankpin from Jampot spares. Then took the crank, new crank pin and conrod to an engineering company I used 35 years ago when rebuilding bike engines. Anyway after a discussion the old guy said he'd done loads over the years (I was also getting a rebore at the same time) and they would call when it was done. (I made a mistake by not taking the new crankpin out of it's plastic covering to check it first so I don't know if I started with problems or if the problems were caused during the building up of the crank – I suspect the latter).
A couple of weeks later I went to collect it. He said the conrod seemed to get tight after it was turned a few times but it shouldn't be a problem.
When I got home I had a closer look and feel. It was as if the big end was wandering across the pin (Which could only be a wander of a couple of thou) then got tight enough that there was no way the conrod would rotate down under it's own weight. I also noticed that the Drive side nut on the crankpin still had about a thread width to go First I put it in a lathe and turned the crank while holding the conrod straight with a bunggie – thinking this may free it off, ran it at about 100 rpm for about a total of 10minutes stopping to feed in more oil every so often via a syringe through the timing side oil hole. But still the bigend would tighten up every four or five turns.
So next I split the crank again. I couldn't really find anything except the rollers and conrod were very tight to get off. Next I looked more at the crank pin length. It measured the same as the original but the shoulder for the timing side was smaller So how could this be?
Next I found a misalignment of the oil holes in the new crank pin axially, you'll see in the next picture with a pin dropped through at the edge of the hole, so misaligned axially by about 1mm. Additionally the pin wouldn't drop through the other pair of holes (There are 4 holes in 2 pairs 90 degrees apart). So I presume that the outer is rotated 90 degrees from where it should be as well. Once I found this I tried the pin in the old crankpin and found it wouldn't go through any of the 4 oil holes – so this probably explained the original trouble with the big end.
Next when checking the new bearing surface in the big end of the conrod I thought the conrod was bent and sure enough checking on a flat surface it definitely was.
So now the questions:-
Has anyone had problems with 2 part crankpins where the outer part has moved with respect to the inner shaft?
Can anyone recommend someone that has the tools and know-how that could rebuild the crank correctly pushing out the bearing race from the conrod bigend and into a new (Second hand) conrod I have, along with any machining that may be required to get the big end moving freely and then balance the whole lot with the new Gandini 40 thou oversize piston I have which is heavier than the original wirewound?
I stripped it due to lots of bad noises after a run, at first I thought piston slap and sure enough about 0.5mm. However then took the barrel off and found I also had about 0.5mm lift on the conrod so the bigend was goosed too.
Split the crank and found the pin, rollers and conrod bearing surface all in a bad way.
Bit the bullet and ordered a new crankpin from Jampot spares. Then took the crank, new crank pin and conrod to an engineering company I used 35 years ago when rebuilding bike engines. Anyway after a discussion the old guy said he'd done loads over the years (I was also getting a rebore at the same time) and they would call when it was done. (I made a mistake by not taking the new crankpin out of it's plastic covering to check it first so I don't know if I started with problems or if the problems were caused during the building up of the crank – I suspect the latter).
A couple of weeks later I went to collect it. He said the conrod seemed to get tight after it was turned a few times but it shouldn't be a problem.
When I got home I had a closer look and feel. It was as if the big end was wandering across the pin (Which could only be a wander of a couple of thou) then got tight enough that there was no way the conrod would rotate down under it's own weight. I also noticed that the Drive side nut on the crankpin still had about a thread width to go First I put it in a lathe and turned the crank while holding the conrod straight with a bunggie – thinking this may free it off, ran it at about 100 rpm for about a total of 10minutes stopping to feed in more oil every so often via a syringe through the timing side oil hole. But still the bigend would tighten up every four or five turns.
So next I split the crank again. I couldn't really find anything except the rollers and conrod were very tight to get off. Next I looked more at the crank pin length. It measured the same as the original but the shoulder for the timing side was smaller So how could this be?
Next I found a misalignment of the oil holes in the new crank pin axially, you'll see in the next picture with a pin dropped through at the edge of the hole, so misaligned axially by about 1mm. Additionally the pin wouldn't drop through the other pair of holes (There are 4 holes in 2 pairs 90 degrees apart). So I presume that the outer is rotated 90 degrees from where it should be as well. Once I found this I tried the pin in the old crankpin and found it wouldn't go through any of the 4 oil holes – so this probably explained the original trouble with the big end.
Next when checking the new bearing surface in the big end of the conrod I thought the conrod was bent and sure enough checking on a flat surface it definitely was.
So now the questions:-
Has anyone had problems with 2 part crankpins where the outer part has moved with respect to the inner shaft?
Can anyone recommend someone that has the tools and know-how that could rebuild the crank correctly pushing out the bearing race from the conrod bigend and into a new (Second hand) conrod I have, along with any machining that may be required to get the big end moving freely and then balance the whole lot with the new Gandini 40 thou oversize piston I have which is heavier than the original wirewound?