E: Engine Big End Replacement

Cyborg

Cyborg

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I did a bit of reading and came across some old HD info about using Loctite RC40 on some of their crank pins. It has about a 3 hour setup time, so allows for truing. It appears (I stand to be corrected) that RC40 has been superseded by 648 which sets up right away. I suppose it could still be used on one side (the one with slightly less interference fit) as long as the pin goes in perfectly straight.

passenger0_0
Good point about the centres. I don't really have a proper way of checking or grinding them on a disassembled crank..... unless I can attach a crank half to a rotary table and do it in the mill. I'll have to ponder that for a bit.
 
Cyborg

Cyborg

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So figured out (obviously still learning here) that I could put the halves between to centres on the lathe and measure the runout to check the centres on the crank.
The timing side is right on. The drive side indicates between .0005" and .001" out at the bearing surface, but the inboard centre on the drive side mainshaft is questionable so it most likely accounts for some or perhaps all of the runout. The centre on the outboard end of the drive side mainshaft "looks" good.
 
Bill Thomas

Bill Thomas

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Cyborg said:
I did a bit of reading and came across some old HD info about using Loctite RC40 on some of their crank pins. It has about a 3 hour setup time, so allows for truing. It appears (I stand to be corrected) that RC40 has been superseded by 648 which sets up right away. I suppose it could still be used on one side (the one with slightly less interference fit) as long as the pin goes in perfectly straight.

passenger0_0
Good point about the centres. I don't really have a proper way of checking or grinding them on a disassembled crank..... unless I can attach a crank half to a rotary table and do it in the mill. I'll have to ponder that for a bit.
Click to expand...
If you use my mod' with a roller between the shaft and wheel you won't need loctite. Cheers Bill.
 
Cyborg

Cyborg

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Bill Thomas said:
If you use my mod' with a roller between the shaft and wheel you won't need loctite. Cheers Bill.
Click to expand...

It's the crank pin that I'm wondering about using the Loctite on. I think the shafts will be fine.... it won't produce enough power to hurt itself and I'm too old and brittle to ride it like I stole it. It's just that one of the crank pin holes looks like it could use some help staying put. It may be ok as is... just waiting for an addition to my bore gauge collection.
 
Bill Thomas

Bill Thomas

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I have a Twin crank assy, Very few miles on it, And it has shutoff the oil supply, I wonder if the T/shaft has turned, So I will fit rollers to both shafts from now on, The mills pins are not strong. Cheers Bill.
 
T

timetraveller

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OK Cyborg; that is correct. It sounds like you have access to some good equipment to check the centre of the crankpin hole and it is worth doing. The one I mentioned above is the only one where I have seen this problem out of tens of them and I suspect it was a mismatched pair of flywheels that had come from different sources. Whether the works made them so that they could be interchanged or made them in batches which were all matched but perhaps a few thou different from each other I don't know. David, who regularly contributes on here, would know. Remember that a six thou run out on one side is only three thou difference in the centre to centre distance. When racing I always used the mod described by Bill of pegging the drive side main shaft into the flywheel with a quarter inch roller. You are right that it should not be needed for road use but can do no harm. Picadors and some racing engines used larger diameter drive side main shafts, 1.125" versus 1.0", to overcome the problem of the shafts turning in the wheels.
 
Vincent Brake

Vincent Brake

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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...

2016-11-02 18.20.03.jpg
 
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