Flywheel splitting/big end replacement

[Paul Gasson]

Hello, today I started to evaluate my winter project, which is to make roadworthy a 1950 NH. It’s fairly complete but not been used for decades so everything needs looking at. The whole engine is worn out, the piston was rust seized but I managed to get it moving, I will have to replace the barrel as the rust pits are too deep to rebore. My question is regarding the big end, it’s totally worn out and needs replacing. I do not have the equipment to split flywheels and wondered if anyone can recommend someone (member or business) in the north west of England who could help me? I will need a new big end assembly and read that there is a locating pin on the taper which can be fitted in different holes according to model? Any advice regarding this would be most welcome to prevent incorrect assembly. Paul

[paul.jameson]

There are several potential people to help you. If you turn up at one of the Lancs Branch meetings I am sure you will get advice on who to use.

[Vincent.vanGinneke]

Hello Paul, splitting 350cc flywheels is not a big thing.
These bigend's have a taper where it fits in to the cheeks.
Loosen, but dont take of 1 bigend nut and give the nut a hefty blow with a pounds hammer.
That will free one side.
I do this with the assembly in my lap, not in a vice or so.
same action on the other side.
When you have the bigend out you can -obviously- see how the arrangement is with the locating pin.
It is just that, a locating pin. it's there to make sure that the oilway lines up correctly.
When fitting a new bigend you can check if the oilway lines up by looking in the sludge trap hole.
If the oilway in that new bigend does not line up, remove the pin. (if it's there at all)
succes.

[Paul Gasson]

Thanks for your positive suggestion Vincent. If you think it should not be too difficult with just my hand tools I will try. Regarding the big end nuts, do you use a socket, box spanner or something else. I imagine they will be tight? Do you remember the size?

[Vincent.vanGinneke]

I forgot; I clamp the cheek that I want to undo the nut from in the vice (you need a large vice)
Undo with a socket, + a lenght of tube.
Can't remember the size atm but sometimes they differ a bit depending on who made the bigend.
I'll have a look tomorrow.


30-9-'21 - The nuts on my R&M bigend are 1-3/16"

[Paul Gasson]

Vincent, thanks for size information and I note your comment about possibly different sizes depending on maker but will start looking for large sockets and a long extension piece!

[garycullen]

Paul, I split the flywheels from my VB600 to replace the big end myself.
A tip I read elsewhere on this forum suggested grinding off the end of two sockets to remove the entry bevel so that more of the driving faces fitted over the big end nut. This is important as the big end nuts are half thickness on my VB so I assume same for your 350. One socket for each side. I also bought sockets with 6 drive faces as these will resist slipping over the corners like 12 point sockets are likely to do since some force might be required to move the nuts.
I know mine were tight. I used a standard socket wrench on one side, locked to the carpeted floor of my garage with one foot, then using a long socket bar the other side nut released with a small crack!
This left me with one flywheel with the big end attached which I mounted in my vice and used the long bar again to release it. Putting it all back together with a new big end and aligning the fly wheels is a whole other story.
Cheers
Gary

[garycullen]

Paul, meant to add that you shouldn’t need an extremely long extension bar, mine is 580mm tip to tip.
1/2 square drive. I couldn’t find any torque numbers to use when rebuilding except guidance to make sure “really tight”
I decided to use some copper grease, small amount on the threads and fitted one side with fly wheel in the vice using the long extension to “really tight” then back on the floor to fit the other just tight, using a square across the flywheel edges to get it near enough then in the lathe with a DTI to check, back to the floor to make adjustments and final tighten and DTI recheck.
I think the copper grease allows you to get more tightness, others may have a better explanation for this.
Gary

[nevhunter]

Why not send the lot to Alpha bearings. They've done that sort of thing in the past and it's a very straightforward job for them. It's the heart of your motor and they make all the bits so can get better fits for things like the hard bush in the conrod eye. Nev

[Paul Gasson]

Gary, thank you for the information, it gives me more confidence to have a go, having found the right tools. I have a precision straight edge but no lathe to put the assembly on. I read that back in the day scribed lines across the flywheels were used as reference lines when assembling, assuming the assembly was correctly aligned previously. Not sure I can trust that looking at the general condition of the engine.
Nev, thank you for your comment. I contacted Alpha for a big end price, but did not know that they would do the complete swap over and as I need a small end bush fitting and honing, it would be great if they could do it all. I will contact them again for a price.