Big end nuts

[simon.holyfield]

Folks, I'm currently assembling the FH bottom end and I've hit a snag. The big end nuts are fouling the crankcase on the timing side.

I've used new bolts, washers and nuts from Draganfly. What should I do? Seek an alternative nut? Delete the washer? Grind out the case?

[Simon.Gardiner]

Simes - it's been a while, remind us please which cases you're using (CNLF or LF) and which crankshaft, big journal or small journal?

SG

[simon.holyfield]

Simes - it's been a while, remind us please which cases you're using (CNLF or LF) and which crankshaft, big journal or small journal?

SG

Sure. These are CNLF cases with a big bearing crank & rods.

[Mick D]

Hi Simon

Have you shimmed the crank to set the end float yet? Why not just compare the old and new components and see where the discrepancy is? Is the contact the result of big end movement not being restricted by the pistons in the bores?

I used the original bolts etc. as they are positively locked with new cotter pins and had no clearance issues.

Regards Mick

[simon.holyfield]

Unfortunately I didn't have the old nuts Mick - the engine was partly disassembled.

I'm on shimming round 2 - I'm waiting for another 0.1 mm (4 thou) to come in the post, so it's almost there.

I found that if I manually hold the drive side rod in the centre of the bore (no piston fitted yet) it appears to clear the case in that the rod will swing when the timing side has fouled - the timing side will still foul if the little end eye is in the centre of the bore.

It would be good to know what thickness the original nuts and washers had. I don't need to lose much - a millimetre would probably do it.

[Mick D]

Hi Simon

I've attached a snag from a disassembly photo, it's the best I have of the nut, may give you some indication of where to concentrate:

Big End Nut.png (226.75 KiB) Viewed 489 times

Regards Mick

Edit: Just looking on the Draganfly website I see there are two types of nut, are you using the self locking ones, the castelatted ones are reduced hex size!

[simon.holyfield]

That's perfect Mick, thank you. Interesting that your nuts don't use separate washers.

I'm using the self locking nuts which as you say are bigger. I have no holes in my rod bolts.

[Mick D]

Hi Simon

From memory there is a thin steel washer, (C 0.012"), under each nut - know anyone with a mill who could cross drill the bolts for you?

Regards Mick

[Roger Gwynn]

The clearance with the large journal crank is very tight and whichever nuts you use I would use the washers, always good practise on aluminium as it spreads the load. The solution is to sand/grind a small amount from the c/case, you will find it is a small amount.

[Mick D]

Hi

The issue with grinding to clear is that if the nuts are moved you may have to repeat the operation. It looks like the Draganfly washers are standard design, better to source some thin ones, and if that doesn't give the required clearance cross drill the bolts and fit castellated as per design. Shame the bolts don't come cross drilled.

Regards Mick