Building a crank D.I.Y

[Magalluf]

I would presume that to build a crank D.I.Y there is a bit more involved than to take an old GP crank and a RD350 conrod to the local expert and to ask for the conrod to be swoped over. Can anyone explain what else is involved, are there any special parts that need to be obtained like the pin or the big end bearing, is there any machining involved etc.

I know there are many shops willing to sell quality cranks but for the people with limited budgets or those living for example in New Zealand or Argentina shipping costs from the UK make buying overseas non viable.

I have never seen advertized the process in detail eg in Scootering so any links or info would be great not just for me but for many other scooterists

cheers

Steve

[Wayne Miller]

I would presume that to build a crank D.I.Y there is a bit more involved than to take an old GP crank and a RD350 conrod to the local expert and to ask for the conrod to be swoped over. Can anyone explain what else is involved, are there any special parts that need to be obtained like the pin or the big end bearing, is there any machining involved etc.

I know there are many shops willing to sell quality cranks but for the people with limited budgets or those living for example in New Zealand or Argentina shipping costs from the UK make buying overseas non viable.

I have never seen advertized the process in detail eg in Scootering so any links or info would be great not just for me but for many other scooterists

cheers

Steve

First you'll need to find out the internal and external diametre and the width of a GP conrod. Do the same with the RD350 cod rod. Get the RD350 conrod machined to the diamentions of the GP rod, get a few oil ways machined in. Then if your tolerances are all correct it should be a straight swap. Make sure your internal diameter is spot on else youll fook up your bearings and then your engine, basically get a fookin good engineer to carry out the work because if it aint right pop goes your engine

[shocky]

I would presume that to build a crank D.I.Y there is a bit more involved than to take an old GP crank and a RD350 conrod to the local expert and to ask for the conrod to be swoped over. Can anyone explain what else is involved, are there any special parts that need to be obtained like the pin or the big end bearing, is there any machining involved etc.

I know there are many shops willing to sell quality cranks but for the people with limited budgets or those living for example in New Zealand or Argentina shipping costs from the UK make buying overseas non viable.

I have never seen advertized the process in detail eg in Scootering so any links or info would be great not just for me but for many other scooterists

cheers

Steve

im sure there are places in the countrys u mention thet do crank rebuilds
whats involved.... hammers wedges and LOTS of skill

[dirtyhandslopez]

When you have the machinst build a RD/GP crank, have them spread the amount needed to be removed between the conrod and the crank flywheels, otherwise you so lose that added beefyness of the RD conrod.
Now, truing cranks up is a whole 'nuther deal. So far I am over 40 hours into trying to learn and all I have manged to do is bugger up a few cranks .
There was an article in Scootering years ago about truing cranks, anyone remember what month/year?
I seems to me, truing cranks is one of those things you just have to do over and over again to get it right, you can't just read it in a book and do it.

[Magalluf]

To be honest I have a failrly good machinist near to me but as I say do I just turn up with a crank and a rod and say there you go mate it´s a straight fit or is there more involved. What about the spacers that go either side, doesn't the Lambretta rod use a 22´9 cm pin or do you use the RD350 pin. Surely there is someone here who has built one up before.

cheers all

Steve

[storkfoot]

I got a 110 rod fitted to an Indian GP 200 crank about a year back. I had this work done at a local company who are wholesalers and retailers of m/bike conrods and pistons, amongst other bike bits. There must be someone similar in Spain?

I went for a Kawasaki KE175 conrod rather than an RD250/350 because it was easier. The pin, little end, and big end bearings came as part of the kit. Cost me £60, including price of conrod kit, to get fitted and balanced [?] on their machine.

If memory serves me right, this was because the Kawasaki conrod had a 15mm wide big end and went straight in (it did have to have the crank pin machined down as it was too wide though). The RD 250 or 350 rods need to have the webs machined down to 11.65mm to get an overall crank width of 41mm, I think.

[J1MS]

I've had cranks built for me by Grampians in the Past, but now there are many quality cranks with 110 rod kits fitted it's less bother to just buy one of these.
I have access to a press, centres & V blocks, copper mallets wedges clamps & gauges for truing up after.
But I still buy ready made cranks when needed.
I'm not an expert at building cranks but know a little about how it's done, I wouldn't machine all the metal off a big end pin to make it fit between the webs best leave some metal to keep it's strength, some of the rods I used are 15mm at the big end after fitting.
I run most with big end shims but have fitted some without.
The problem with some pins off Japanese kits is they fit very tight in the webs compared with Lambretta pins & some cranks webs can crack if the pin is too tight Japanese webs normally have much wider webs which helps to spread this loading.
Big end shims I've used some in the past off a Vespa P200 (I think) but that was a while back when I was doing Jap barrel conversions, which I have little to do with now.

[dirtyhandslopez]

I wouldn't machine all the metal off a big end pin to make it fit between the webs best leave some metal to keep it's strength

JIMS, do you mean con rod here? Surely if the big end pin is to long, just cut to the correct length, shouldn't affect anything. Keeping the beefyness of the big end of the conrod is one of the reasons for fitting them.
Many ways to get the conrrods to fit, but I would get(or have one cut to the correct length) a big end pin. Add together the width of the webbs,conrod, bearing and shims(2 x .5mm) add in .006(?) for clearance(.003 on each side) See what the difference in the two measurements is, divide that number by four(four areas are avalable to take metal from: each side of conrod and each crank webb), then take the amount you end up with off of each surface. The machinst has to make four cuts on different parts, so expect some labor time for that.


P shims are usable and also Wiseco do different thickness shims if needed.

Or just buy a ready made crank, as JIMS said

What is the trick to truing them up JIMS? Just keep doing it?

[J1MS]

Yes I meant Conrod, it just dosnt read like that now you've pointed it out.

As for trueing crankshafts... A lot of luck.... and a big brother that knows what he's doing is a major plus...

[dirtyhandslopez]

Can I borrow your big brother?