RECONDITIONED CRANK ASSEMBLIES

[Trev Sellars]

Thanks Jess for the support. I have been discussing this with Jess, and Richard T in the Forest, and the conclusion is, If the crank goes at the moment the bike is pretty much scrap. At the moment, the approximate cost of rebuilding a crank is around £750 to £800. So, as Jess has indicated, I am trying to source a solution that is both a "good fix" and at a reasonable cost, to the bike owner. At the moment, the biggest issue is the main journals wearing, causing the mains bearings to be sloppy. I have found a supplier in the UK who can supply a reduced internal dimension bearings of 24.8mm, instead of the normal 25mm. This would prove to be a good low cost alternative, and keep the bike original, IF the rest of the crank is ok. The roller bearings for the CON ROD can be sourced and if the existing con rod, looks to be sound, the entire crank assemblty can be taken apart and rebuilt. Then, the smaller I.D bearings can be used, to good effect. I attach a screen shot of the bearing supplier but the bearings are over £70 plus vat plus postage. Incidentally, the cost for machining the journals, replating them to original spec, is about the same. With help from club members, Richard and Alan, I have found a couple of guys local to me that can do the above BUT as usual, it takes time. Possibly 3 months delay! I have spoken with the ARIEL OWNERS CLUB COMMITTEE and I am hoping that they can fund the first batch of 10 cranks to be done and put into stock. The real problem is, the stock of original con rods is running low, so what alternative do we use? and what knock on effects relating to different con rod lengths cause. AND will people accept a single solution to this problem as the last thing we need, is different requests for different con rods to be used. I think for general bikes NOT racing bikes, the single agreed approach would be the simplest and keep the cost down. Well, what are your thoughts on this?

[nevhunter]

My solution to this Has been fit New drive side shaft. Often the spline is worn too. IF you DO change overs you will end up with some unusable flywheels and perhaps some Mixed ones.. I wouldn't put myself in that Position, frankly. and if the ends of a shaft have had the centres damaged, you can't successfully grind them. People like Carrillo Make new rods (to their style) or you might be able to get New JAWA rods .Nev

[Trev Sellars]

Thanks Nev for your input to this debate and your advice.
I have 12 cranks to refurbish and as you suggest, some do have worn shaft ends and some have been damaged, to put it politely.

It may be the best approach to try and source a complete new crank assembly, however I cannot locate the original drawings or specificatiuons to get an accurate detail for the machine shop to work to and come up with a price.
Does anyone have an original drawing I could copy?

Thanks

[Simon.Gardiner]

Trev

There are several Forum refs to using Lambretta conrods and bearings, I guess either with modified crankpins or maybe flywheels modified to take the Lambretta pin. Brian H (bh_sprint) seems to be using this setup, but if you've been discussing with Jesse I'd think you''d have worked over this option.

There's also a Forum reference to using 'rm125 rods and GT pistons' which might be another option to work over if we could get more details.

However, the mainshafts are going to be an issue - I've seen a set of fully reconditioned cranks on ebay before now, from one of the very reputable 2-stroke shops (Nametab of maybe Fahron) I'm pretty certain they stated chromed and reground shafts so I wonder if t would be possible (or worthwhile) to get a dozen or so sets of shafts reconditioned.

Drags are still offering exchange reconditioned cranks, might be interesting to know if they can do anything with the shafts if they get something with worn ones....

SG

[Roger Gwynn]

If you read the relevant Draganfly page you will see that they talk of the major problem being the wear on the shafts and the fact that all their reconditioned crankshaft assemblies include grinding and hard chrome plating the shafts back to size. They have been doing this for around 40 years. A set of exchange cranks including con-rods is about £490+VAT and refurbished con-rod assemblies £300+VAT per pair. If you talk to them I think you will find that they have lots of old flywheels to replace the odd ones that re not reclaimable.
https://draganfly.co.uk/product-categor ... t-2stroke/

[bh.sprint]

Re the Lambretta conrods. I put Lambretta rods in the Arrow engine but it needed crank pins making which puts up the price . It did mean I could also have needle rollers in the little end which reduces the chance of them seizing up and that engine has been revved. Also had 110 m/m conrods in the MK2 Leader engine , the flywheels needed boring out to accept the bigger crank pins but it works and the piston timing is slightly different which seems to give the engine power in the lower revs, just what is needed on a Leader -- the extra 20 cc also helps -- it has a 270cc capacity.