Repair of worn or damaged crankshaft big end pins

[James P]

Has anyone managed this successfully?

So far I have managed to get only one "good" complete crankshaft out of three used ones ! Damage or advanced wear to the big end pins made two sets of the inner crank webs unusable. Of course, there are a couple of topics on the forum which have partly dealt with this issue, but no solutions so far.

There does not seem to be enough material to bore a hole for a plain/straight press-fit big end pin (i.e. pressing in a new pin would cause the new hole to collapse into the existing hole for the centre shaft).
It would be possible to bore a smaller hole and make a special stepped big end pin, but the smaller contact area would likely increase the chances of the pin moving during use (causing the crank assembly to twist). There may also be problems with stress at the step, unless special attention was paid to providing a suitable radius (which would have to be duplicated on the crank web to allow proper fit). Welding the new pin in place may lessen or eliminate the likelihood of the crank assembly twisting.

This is all very well in theory (well...my limited knowledge of the theory ), but has anyone actually tried it out? Does anyone have any other suggestions for achieving the same objective? I don't know of any type of electroplating which would be suitable for this application and I'm not sure whether grinding down and sleeving the existing big end pin would be a viable option.

Another option may be to find a way of coupling together two KX125 (or other suitable) crankshafts and also providing a means of accommodating the balancer drive gear, but the chances of this being easy are remote...

Opinions and advice welcome!

Thanks & regards,
James

[scooble]

I believe MJ was toying with the idea of using two seperate cranks joined at the ballancer gear. Might be worth PM'ing him to find out more

[TwoStroke Institute]

Your thinking too much No problems using a stepped crank pin, they work perfectly and no need for radiusing etc etc. Kawasaki triples early TZ's and the mighty Bighorn all ran stepped crank pins. Recently offset ground a few for strokers no problems at all.

What causes a crank to twist and spread is a 'rocking couple' the balance shaft virtualy eliminates the couple.
You can have the big end pin ground down, then hard chromed and then ground to final size, you could soften the web machine off the damaged part of the pin, machine a sleeve have it vaccum brazed on then heat treated and final ground back to size (last attempt at that wasn't successful but it was not softened, brazed and hardened rather a sleeve was welded on).

The best option would be to buy some EN36/39B, have it heat treated and then water jet cut the OD ,pin bore and centre hole with tighter interference fits. Then you have the full width to press in a standard 22mm crank pin.

[James P]

Your thinking too much

Hmm, perhaps...that could be the reason my head hurts

Thanks for the suggestions, but I have more questions:

Regarding the stepped big end pin: Should the new pin be made solid? The present fixed pin is 22mm OD and hollow (10mm ID). What would be a suitable OD for the step portion of a new pin, bearing in mind that the adjacent hole for the centre shaft is 25mm ID?

Regarding the grinding and hard-chroming: How long could this be expected to last? I'm certainly no expert, but always thought that hard-chrome was not a suitable finish for needle roller bearing surfaces.

...machine a sleeve have it vaccum brazed on then heat treated and final ground back to size...

What would be a suitable ID for such a sleeve?

The best option would be to buy some EN36/39B, have it heat treated and then water jet cut the OD ,pin bore and centre hole with tighter interference fits. Then you have the full width to press in a standard 22mm crank pin.

I presume you mean "make a new crank web"...? Whatever material one uses, would not the same problem exist with the holes for the big end pin and centre shaft being too close together?

I'm not particularly knowledgeable when it comes to metallurgy (or anything else, for that matter ...my head is hurting again ). Anyone know anybody at the Kawasaki factory who has access to the old CNC/CAM programs and could knock up a few dozen inner crank webs after work in exchange for a carton of beer?

Regards,
James

[James P]

I believe MJ was toying with the idea of using two seperate cranks joined at the ballancer gear. Might be worth PM'ing him to find out more

Thanks for the lead. Once I've had my remaining crankshafts stripped and find them all knackered, I'll definitely be making enquiries in that direction!

Regards,
James

[TwoStroke Institute]

Your thinking too much

Hmm, perhaps...that could be the reason my head hurts

Thanks for the suggestions, but I have more questions:

Regarding the stepped big end pin: Should the new pin be made solid? The present fixed pin is 22mm OD and hollow (10mm ID). What would be a suitable OD for the step portion of a new pin, bearing in mind that the adjacent hole for the centre shaft is 25mm ID?

Regarding the grinding and hard-chroming: How long could this be expected to last? I'm certainly no expert, but always thought that hard-chrome was not a suitable finish for needle roller bearing surfaces.

...machine a sleeve have it vaccum brazed on then heat treated and final ground back to size...

What would be a suitable ID for such a sleeve?

The best option would be to buy some EN36/39B, have it heat treated and then water jet cut the OD ,pin bore and centre hole with tighter interference fits. Then you have the full width to press in a standard 22mm crank pin.

I presume you mean "make a new crank web"...? Whatever material one uses, would not the same problem exist with the holes for the big end pin and centre shaft being too close together?

I'm not particularly knowledgeable when it comes to metallurgy (or anything else, for that matter ...my head is hurting again ). Anyone know anybody at the Kawasaki factory who has access to the old CNC/CAM programs and could knock up a few dozen inner crank webs after work in exchange for a carton of beer?

Regards,
James

Still thinking too much. If the pin and the centre shaft bores being too close together was an issue no TZR's or RGV's would still be running(or made).

Big issue with the KR-1 crank web is where it is waisted down where you need some meat to EDM the pin away would leave no material. From looking a banshee stroker cranks about 3-4mm outboard of the pin bore seems to be as fine as they cut it.

No body needs and CNC CAD CAM or what ever with a simple 2D drawing of a 88(??)mm dia web 15mm(??) thick with a centre hole raduis 12.46mm and one hole on a 25.3mm PCD 10.46mm radius.

A sleeve with 2mm wall would be fine. The hard chroming is something I mixed up with the bearing/seal journal, it's used in karting all the time, but not the crank pins it's for the bearing journal.

[James P]

Still thinking too much. If the pin and the centre shaft bores being too close together was an issue no TZR's or RGV's would still be running(or made).

I can't comment on RGV cranks, but all the TZR cranks I've seen use the same style of fixed big end pin as the KR1. I can only imagine that similar problems would be encountered in trying to make a new full size (i.e. same diameter as original pin) hole for a press-fit big end pin in TZR crank webs. However, I accept the notion that a special stepped pin may work.
I have seen new inner crank webs on sale for the 1KT-based TZRs (not sure of quality though), so that would be my first port of call for rebuilding a worn-out TZR crankshaft. Sadly not yet seen similar parts available for the KR1 .

No body needs and CNC CAD CAM or what ever with a simple 2D drawing of a 88(??)mm dia web 15mm(??) thick with a centre hole raduis 12.46mm and one hole on a 25.3mm PCD 10.46mm radius.

True - my comment you are referring to was just my attempt at humour...or wishful thinking perhaps .

Thanks for your suggestions though. If my remaining crankshafts have any knackered big end pins, I'll be further investigating the special stepped big end pin or the sleeve.

Regards,
James

[TwoStroke Institute]

Maybe the close proximity is an issue but you can do what is done with Yamaha KT100 S/J cranks, the crankpin and bore have a very loose interference fit, until a hardened 'welsh plug is pressed into the hollow crank pin, it expands the pin slightly for better interference fit than just relying on pin and bore size. Because of that the cranks last indefinantly. To remamufacture a integral pin web is not hard just a waste of material.
Why not send a web up to Graham at crankshaft rebulding services and let him come up with a solution, he's good at that kind of thing.

[James P]

Maybe the close proximity is an issue but you can do what is done with Yamaha KT100 S/J cranks, the crankpin and bore have a very loose interference fit, until a hardened 'welsh plug is pressed into the hollow crank pin, it expands the pin slightly for better interference fit than just relying on pin and bore size. Because of that the cranks last indefinantly.

I had seen pictures of this arrangement somewhere, but had forgotten about it! I didn't realise the Yamaha kart engines used this set-up. This may be worth investigating, but if a straight (non-stepped) big end pin is employed, both the pin and centre shaft would likely need these plugs.

To remanufacture a integral pin web is not hard just a waste of material.

Certainly not hard, but quite expensive for those without machine tools! However, still an option worth considering.

Why not send a web up to Graham at crankshaft rebulding services and let him come up with a solution, he's good at that kind of thing.

Also worth investigating. Once I've determined exactly how many of my big end pins need repairing, I'll actively look for a solution (don't want to incur too much expense at this stage). My own crankshaft man has already agreed that the stepped pin or sleeve repairs could be done, but understandably has reservations. I understand that CRS Graham is well-regarded, so will keep him in mind.

Thanks & regards,
James

[TwoStroke Institute]

I checked and the proximity of the 2 bores is the reason for the integral pin. Stepped pin can work. James remanufacturing a web is not a job for the home machinist unless you have some good cylindrical grinders. If you CNC machined 10 or 20 blanks and have them heat treated would not be that expensive. The cylindrical grinding of pin and bore is where all the time is.

Asking for a quote costs nothing.

[James P]

I checked and the proximity of the 2 bores is the reason for the integral pin. Stepped pin can work. James remanufacturing a web is not a job for the home machinist unless you have some good cylindrical grinders. If you CNC machined 10 or 20 blanks and have them heat treated would not be that expensive. The cylindrical grinding of pin and bore is where all the time is.

Asking for a quote costs nothing.

Thanks. I haven't ruled out any option yet - it just depends on the condition of the rest of my crankshafts! I have other projects to attend to at the moment, but will make a decision once I've stripped the remaining engines.

Regards,
James

[scooble]

I have a worn crankshaft, so, if you find a good solution, I would like to build a crank with RD rods and Mito pistons

[500bernie]

Didn't someone post a while back offering billet crankcases, sounds like the perfect solution to stroking the bike and using a more available crank. Assuming they could make changes to accomodate a different crank with longer rods.
Going to see if I can find the post now

[TwoStroke Institute]

The only real options are a stepped pin but there is a lot of material waisted down off the OD of the web or just biting the bullet and remanufacturing the web with the integral pin.

[KR-1R]

http://www.pjme.co.uk/acatalog/Kawasaki ... m_End.html