E: Engine Big End Replacement
- Thread starter Cyborg
- Start date
I had this goofy idea that I could set up a mandrel to hold the outer race and size it with a tool post grinder on the lathe if I knew roughly how much they shrink when installed. I have a few rods and a few outer races, so could do one outer race slightly too large , fit it to the rod and then when installed on the bearing I would know what to hone the next out race out to. Might take a few tries.... never mind... clevtrev set me on the straight and narrow. I'll drive across town and drop off the b/end bearing and rod at the machine shop. Have I mentioned that I hate sending stuff out.......
I remember talking to Laurie Binns about this. He said that he most frequently found, when fitting new eyes to rods (E5PM or equivalent) that they distorted inward at three equidistant point on the inner circumference. I haven't read enough poetry to understand this phenomenon.
I have just had my crank rebuilt for the third time in around 80,000 miles.
The first two times it was done by a now deceased local 'expert'. The first time he did it he fitted an oversize crank pin which involved boring out the crank pin holes in the wheels, lightened the flywheels and 'pin bored' (his term not mine) both ends of the conrod. That big end lasted less than 5,000 miles before total failure caused, according to the same expert,by poor case hardening of the crank pin. The second job he did on the crank lasted around 20,000 miles.
The chap that fitted the latest crank pin reported the following issues with my crank assembly. 1. Each flywheel as wedge shaped - he assumes that when the wheels were 'lightened' it was not done in a mill or a surface grinder but by some other less accurate means resulting in the face of each wheel NOT being parallel. 2. The crank pin holes in the two flywheels were 0.007" different in their relationship to the main shafts - so each wheel was giving a different stroke. 3. The crankpin holes were not an interference fit, but rather an easy slip fit with just the pressure of the crank pin nuts holding things together. The result of this was that while the main shafts were running more or less true, the crankpin itself was at a slight angle relative to the main shafts and to the conrod - as a result the entire load in the big end was focused on one end of the big end bearing rollers with no load at all on the other.
It was touch and go but he managed to save the flywheels but it took over 10 hours of machine shop time to fix them - and that excludes the time he spent to assemble the new big end once the wheels had been repaired.
Having only just finished putting my Comet all back together with the only 'new' bits being main bearings and the rebuilt bottom end I can tell you that it is performing was way better that it ever has in the past.
So when it comes to rebuilding a crank assembly it not just the main shaft runout you should be checking. You need to check and double check all of the dimentions around the crank assembly - assume nothing!
I wish I had the space, skills and equipment to all this sort of precision engineering work myself so I would not need to send anything out to others.
The first two times it was done by a now deceased local 'expert'. The first time he did it he fitted an oversize crank pin which involved boring out the crank pin holes in the wheels, lightened the flywheels and 'pin bored' (his term not mine) both ends of the conrod. That big end lasted less than 5,000 miles before total failure caused, according to the same expert,by poor case hardening of the crank pin. The second job he did on the crank lasted around 20,000 miles.
The chap that fitted the latest crank pin reported the following issues with my crank assembly. 1. Each flywheel as wedge shaped - he assumes that when the wheels were 'lightened' it was not done in a mill or a surface grinder but by some other less accurate means resulting in the face of each wheel NOT being parallel. 2. The crank pin holes in the two flywheels were 0.007" different in their relationship to the main shafts - so each wheel was giving a different stroke. 3. The crankpin holes were not an interference fit, but rather an easy slip fit with just the pressure of the crank pin nuts holding things together. The result of this was that while the main shafts were running more or less true, the crankpin itself was at a slight angle relative to the main shafts and to the conrod - as a result the entire load in the big end was focused on one end of the big end bearing rollers with no load at all on the other.
It was touch and go but he managed to save the flywheels but it took over 10 hours of machine shop time to fix them - and that excludes the time he spent to assemble the new big end once the wheels had been repaired.
Having only just finished putting my Comet all back together with the only 'new' bits being main bearings and the rebuilt bottom end I can tell you that it is performing was way better that it ever has in the past.
So when it comes to rebuilding a crank assembly it not just the main shaft runout you should be checking. You need to check and double check all of the dimentions around the crank assembly - assume nothing!
I wish I had the space, skills and equipment to all this sort of precision engineering work myself so I would not need to send anything out to others.
The only thing I am assuming so far, is that the previous owner disassembled this crankshaft with a large blunt instrument and he had very poor aim. Perhaps blind.. inebriated.... or both.
I find the fact that you achieved 20,000 miles on slip fit pin holes quite encouraging. I'm still waiting for my new measuring device, but I do know the pin is somewhat larger than the holes in the wheels.
I find the fact that you achieved 20,000 miles on slip fit pin holes quite encouraging. I'm still waiting for my new measuring device, but I do know the pin is somewhat larger than the holes in the wheels.
Read my post again. It was NOT the previous owner.
BTW with the most recent rebuild - the nuts on the crank pin have been tightened to a reported 200 ft lb
As I have said before, I once took my crank to one of our top blokes, And watched him "Hone", The big end eye by winding the rod round a large pin in the vise by hand, With grinding paste, Others on the Forum said this was OK, But it didn't impress me, Maybe I will have to do it at home, But my hole 560 crank will be a Bodge, Fingers and everything else crossed !!. Cheers Bill.
I work part-time in a bike shop and we rebuild quite a few roller bearing cranks, most are ok but we have the odd one that is out of round or too tight (funnily we don't seem to have any too loose)
When this occurs we have a Delapena bench honing machine like this we use to hone them out.
When this occurs we have a Delapena bench honing machine like this we use to hone them out.
Do you know how deep the hardness goes Chris ?, In the outer track, I know there are some rubbish bearings sold now a days. Cheers Bill.