Crank rebuilds at home!

[ferox100]

Hi all,
I've built some cranks with success previously but have come across a problem . I have new centre webs so no previous marks line up to be exactly at the 180 degrees when rebuilding. Anyone here done cranks themselves? If so what method did you use to get the webs exactly at 180 degrees apart?
TIA.
John.

[jon]

I don’t want to sound rude, but if you have to ask that sort of thing, shouldn’t you get it done by someone who knows? I admire your sentiment though and are all for having a go yourself.

Not really sure how to get the webs as close as possible before pressing? Watch some Allen Millyard videos on the subject (if you can bear the constant adverts?). Alternatively might this help?

rdlccrazy.proboards.com/thread/50276/crank-rebuild

I know they are fine tuned in a lathe by holding the centre drillings, and tapped with a copper mallet until the DTI says it’s true. From memory I think the accepted tolerance is 2 thou of eccentricity? Remember watching one of mine trued to 1 thou. All new parts except the clutch side web.

Jon

[zed1015]

Full circle cranks are usually built up using a dedicated tube or pin jig to get the webs as close to the final orientation as possible so that minimal trueing is needed with a copper mallet after pressing up.
It can be done with a good straight edge etc which is more time consuming and reliant on the operators eye but in either case it will still need mallet truing unless you drop lucky.

[steve63]

When I was 16 I took my FS1E to a bike shop to have some new points fitted. Well that's not exactly true. I took it after I'd had a go and then bike subsequently wouldn't start so I panicked and took it in.

Since then I've learned that there is no magic involved in anything to do with motorbikes. It's all just engineering and maths. If you have the time, inclination and aptitude any of it can be learned although it depends on the below.

What I'm trying to say is It's not about the job it's about the person doing the job. For some people changing a plug would result in a stripped thread and or bits falling into the engine but for others a full engine rebuild is a piece of pi$$. I'm all for people having a go, you need to accept which side of the above spectrum you're at 

I recently bought a pair of V blocks, a surface plate and a dial & stand so I can at least check cranks. Re-building one might be too big a leap   

[muttsnuts]

twin cranks are whole lot harder than a single, as Zed has said, you need a pin jig, which holds the big end pins at 180 degrees, that sorts out getting the inners aligned if the inner webs are seperate to the centre pin (depends on the crank etc), the outers are more tricky, but most use a jig again to set them at exactly (or as near as you can) to be true to the inner web you are pressing it onto, some degree of hitting it with a mallet afterwards to true it within spec is generally required, but does depend how good your jig is

[ferox100]

Ok, thanks all for your input, looks like I need to make pin jig to align the centres correctly. The truing side I have no problem with as I've done this several times previously. Now what I really would like is an example of a pin jig in a perfect world . Lol😁.

[liffy16]

Agree with mutts on this single cranks are fairly easy too do ,with twin cranks I came to the conclusion that some sort of jig would have to be made so I never bothered. Pjme,Grampian and a few others do this job for relatively little money I definitely couldn't be bothered now .If you've really got the motivation to do it though then crack on 👍or should that be crank on 😂🤣