E: Engine Big End Replacement

[greg brillus]

The amount of contact area where the pin presses into the wheel is not that high, and the interference is not high either. I would give it some clouts with a good sized copper face hammer and see what happens, as I don't see any harm happening. The runnout should be not more than 0.002" max remember these cranks have four mains bearings not the usual two, so the alignment is more critical.

 

[Cyborg]

The amount of contact area where the pin presses into the wheel is not that high, and the interference is not high either. I would give it some clouts with a good sized copper face hammer and see what happens, as I don't see any harm happening. The runnout should be not more than 0.002" max remember these cranks have four mains bearings not the usual two, so the alignment is more critical.

Well I sat and stared at if for a minute. Given that the high spots are 180 apart and pretty close to 90 degrees from the pin, one blow might do it. Right where I have to hit it, there is some "shop patina" or beaver marks as I prefer to call them, so that is where it received it's prior beatings with something that wasn't copper faced.

I do wonder what sort of reading I would get if it was on knife edge rollers at the inboard ends and dial gauges outboard.

 

[Martyn Goodwin]

Well I sat and stared at if for a minute. Given that the high spots are 180 apart and pretty close to 90 degrees from the pin, one blow might do it. Right where I have to hit it, there is some "shop patina" or beaver marks as I prefer to call them, so that is where it received it's prior beatings with something that wasn't copper faced.

I do wonder what sort of reading I would get if it was on knife edge rollers at the inboard ends and dial gauges outboard.

You MUST find out as that is the critical measurment. See post #127 from Mr Speet (above)

 

[passenger0_0]

Lead blocks are good Cyborg as they don't dent the wheels.
I find it hard to accurately judge the force of a hammer blow so I 'bump' the flywheels by holding one wheel and gently lowering the other onto a large (soft) aluminium block. Here the flywheel acts as its own hammer. Easy to judge the force and do minor adjustments.

 

[Cyborg]

The Only Correct Way checking a crank is over the bearing positions, nothing else comes near.

tomorrow a picture where the cranck is running on...

View attachment 17566

What is the crank running on. Bearings or knife edge rollers? Could you post a picture of the stand please and thank you.

 

[timetraveller]

You just provided the information I was wondering about. 180 degrees apart and at 90 degrees to the crank pin. Have you fully tightened the drive side nut onto the crank pin. If not then that would be my first move. Then you know just where to use the inertia of the flywheels to hit the wood/aluminium or whatever with the timing side flywheel. They do not move easily if the pin is a good fit in the flywheel so you are unlikely to move too far with the first hit. Give it a good thump and then go back and measure it again. I find it pays to write down the value and the direction of the high spots so that if one enters a confused state one knows where one had got to. Good luck with it. If I can do it then anyone can do it.

 

[Chris Launders]

I've found a mark with a marker pen on one flywheel 90 degrees to the crankpin provides a reference to where and which flywheel I'm hitting. I use a copper hammer myself, feels about a kilo (Thor size 2)

 

[Cyborg]

You just provided the information I was wondering about. 180 degrees apart and at 90 degrees to the crank pin. Have you fully tightened the drive side nut onto the crank pin. If not then that would be my first move. Then you know just where to use the inertia of the flywheels to hit the wood/aluminium or whatever with the timing side flywheel. They do not move easily if the pin is a good fit in the flywheel so you are unlikely to move too far with the first hit. Give it a good thump and then go back and measure it again. I find it pays to write down the value and the direction of the high spots so that if one enters a confused state one knows where one had got to. Good luck with it. If I can do it then anyone can do it.

The drive side nut is torqued to 185.... perhaps I should bump that up a bit. I have a bulls eye marked on the timing side flywheel 90 degrees from the pin on the high side. I haven't done any beating yet. I'm going to make some knife edge rollers and measure it with them running on the inboard bearing journals and dial gauges outboard. I'm having difficulty grasping why it would make a difference from measuring it on centres if the centres have been verified ok. Measuring it both ways might cause that dim bulb to light up.

 

[Vincent Brake]

see how i ve done it: (that is, after the big end has been replaced)
2nd picture only to see the 2 x 2 small bearings, to take up the axle.
jig all within 0,015 mm alinged.
i use it also to check: static crank balance, straightness of pushrods, the long hollow main axle etc.
All a part why my engins are rather quiet, and live longer, (well i hope so)

belowpicture shows a balancing work: (i enlarged the 3 smaller holes)

 

[Cyborg]

I'm going to try squaring these up and bolting them to the mill bed. Trying not to make a career out of this and I keep getting interrupted with things like a triplex bird house for the 4yr old granddaughter.