E: Engine Big End Replacement

[Cyborg]

Vincent, I measure them on the main shafts. On the drive side near to and some distance away from the flywheel. On the timing side where the timing side inner bearing goes. The keyways make it difficult on the timing side. I do not measure up on the outside of the flywheels although I know one racer who makes everything a few thou over sized and then cylindrically grinds, main shafts and flywheels so that everything is true to a few tenths of a thou.

Terry Prince says not to check his cranks using the centres. His words " The crank cannot be checked between centres on a lathe, only on knife edges close to the inner bearings as the grinding process does not use the centres and they could be out", so I guess some of it depends on how the crank was made...

His cranks also have a balance factor of 60%.... what do all y'all think about that?

 

[Robert Watson]

First thing to check when you put it in centres is the run out at the ends, and correct the centres with a dremel if needs be.

 

[Vincent Brake]

way to go man

 

[Bill Thomas]

I actually wasn't thinking of motorcycles when I wrote that. I should probably keep my warped sense of humour to myself.....

You should maybe think more about the HOLE in the T/side mainshaft !!. Cheers Bill.

 

[Cyborg]

You should maybe think more about the HOLE in the T/side mainshaft !!. Cheers Bill.

It's all good. I checked that in step one. Cleaned out the passage way and confirmed alignment etc. Given my age and testosterone levels, I seldom think of anything except food, motorcycles, fishing, and where the nearest bathroom is.

 

[Cyborg]

I recall reading in a reprint of one of the first 48 editions of MPH where a Canadian member described the ease with which he replaced a twin big end.All that was needed was a suitable socket,a vice and a straightedge.I don't recall the mention of a large club hammer but I'll bet it was in his tool kit.A lot of the spares I have scrounged over the years have plenty of centre punch and cold chisel marks.Those were the days!

This crank has been subjected to a bunch of abuse. It looks like it was disassembled and reassembled by a troop of baboons that were beating it with large rocks.
As for centre punch marks, this should make you feel nostalgic. You'll notice them surrounding the main bearing housing in a failed attempt to keep the bearing from oscillating around. The screw in the 7 o'clock position is for the bearing retaining plate. It doesn't want to come out because it travels through to the outside of the case and is peened over like a frigging rivet.

 

[Cyborg]

So yesterday, I installed the thrust washers and rod. Lowered the quill to start the T/S flywheel onto the pin. Used a rather crude method (modified puller) to encourage the two parts together (without transferring any forces to the mill) far enough that it would be safe to move the assembly to the press (about 1/3 the way home). Moved it to the hydraulic press and once on all the way, I put the crank assemble between two centres on the lathe. That is all I have at the moment. As mentioned previously I verified that the centres in the crank were true. Now I have a bit of a quandary. I don't know if it was my brilliant use of the mill as an alignment tool or just dumb ass luck, but the rod side clearance is .013" runout on the timing side is .002" and the drive side is somewhere between .0025" and .003" The high points are 180 degrees opposite. Given that Terry Prince does his twin cranks to be within.002 and states that with the usual imperfect case alignment and C3 bearings, it's fine.... along with the fact that I have never beaten a crankshaft in anger (plus this crank has suffered enough) , so the quandary is.... do I just let sleeping dogs lie. I suppose it could still go to hell in a handbag once I torque the timing side crank pin nut.

 

[BigEd]

So yesterday, I installed the thrust washers and rod. Lowered the quill to start the T/S flywheel onto the pin. Used a rather crude method (modified puller) to encourage the two parts together (without transferring any forces to the mill) far enough that it would be safe to move the assembly to the press (about 1/3 the way home). Moved it to the hydraulic press and once on all the way, I put the crank assemble between two centres on the lathe. That is all I have at the moment. As mentioned previously I verified that the centres in the crank were true. Now I have a bit of a quandary. I don't know if it was my brilliant use of the mill as an alignment tool or just dumb ass luck, but the rod side clearance is .013" runout on the timing side is .002" and the drive side is somewhere between .0025" and .003" The high points are 180 degrees opposite. Given that Terry Prince does his twin cranks to be within.002 and states that with the usual imperfect case alignment and C3 bearings, it's fine.... along with the fact that I have never beaten a crankshaft in anger (plus this crank has suffered enough) , so the quandary is.... do I just let sleeping dogs lie. I suppose it could still go to hell in a handbag once I torque the timing side crank pin nut.

View attachment 17700

You have gone to a lot of trouble so far to do things correctly. Why not go the extra "mile" (.0025" - .003") and get it spot on. I doubt being "spot on" will be harmful.

 

[vibrac]

on the other hand those dogs are snoring at the moment but......

 

[Cyborg]

You have gone to a lot of trouble so far to do things correctly. Why not go the extra "mile" (.0025" - .003") and get it spot on. I doubt being "spot on" will be harmful.

Well there is my aforementioned low testosterone levels which helps to keep me in fear of going through the same gong show with the crank as I put myself through tramming the mill. If I knew exactly how many blows it would take and at what velocity with a 15lb lead fishing down rigger weight to move it .001 per, then it would be easier to drum up the courage to do it. I think I'm just going to bask in my glory for a day or so before I proceed. Being spot on won't be harmful, but getting there might be.