Thread: Go Kart, Yamaha crank repair

Hi gang,
I dabble in a bit of Go Karting with a bunch of mates we all run Yamaha KT100s (100cc) 2 stroke motors. The crank bearing journals are a bit soft and tend to wear as the bearing inside race is much harder. The usual repair is to split the crank and send the 2 halves off to be hard chromed. The journals are either machined or ground under size and then hard chromed and ground back to size, 20mm. This is not a cheap fix. In the US they fit crank savers to new cranks these are a hardened and ground sleeve, ID is an interference fit on the 20mm and take the OD upto 25mm, you then run 6205 C4 bearings in the case, the sleeve only covers the bearing width and the standard 36x20x7 seal is run in the case. I have fitted a set of these to the crank which is in my current engine. The sleeves are what could almost be off the shelf needle bearing inners but I believe the crank savers are specifically made ground to give the interference fit on the crank.
The attached pics show one of my other cranks that need repair, I was thinking if I can source needle inners in 25 OD with the ID in any range from 19.5 to 18 mm I could machine/grind (SHER tool post grinder ) down the crank journals for an interference fit with the sleeve. The length would need to go to 25mm which covers the seal section of the journal but 36 x 25 x 7 seals are available so no problem.
I have googled high and low but can not source the required size. If any of the group could point me in the right direction that would be appreciated.

Cheers
Bruce

Go to the ekarting news forums and PM Pete Muller.

http://ekartingnews.com/forums/

If there is anyone in the world who can help you it is him, he no longer works on kart motors but still has an interest and helps out where he can. This is his web page and he has a contact email in the FAQ section so you may be able to get him with that...

http://www.muller.net/mullermachine/index.html

There must be thousands of motors out there that have already been done and not used. An advert on Kartbook.net might get you a cheapie that has a good crank

Hi Chris,
Spoke to Pete a few years back, they only use crank savers in the US, the only repair is the hard chrome fix. And yes he is a wonder of knowledge. Here in AUS adding additional mass to the crank and running different bearings would not be allowed under AKA rules, but for non racing and that I like to do my own engine work I would be happy.

Regards
Bruce

It's interesting to hear that hard chrome is used to fix a worn rolling bearing surface.
I'd read that this isn't a good idea due to it being prone to flaking off - not that I'd know. Does it give good service life for you?

Building up worn metal can also be done by metal spraying, a specialist technique. I used to sent out big shafts out of vibrating centrifuges to be sprayed. It's then ground back to standard size. The firm is A1 Metallising in Sydney. http://www.aonemetal.com.au
It's worthwhile for big stuff, not sure about small jobs but could be worth a call.

If you want to get a press fit where there isn't interference, copper plating is easy and effective. Maybe even Loctite?

Jordan

Hi Jordon,
The crank doesn't run in needle bearings I was only referring to the inners from needle bearings as possible hardened sleeves. Once hard chromed the cranks give good service.
Regards
Bruce

Bruce, there would have to be a thousand chromed cranks out there doing nothing so why repair a damaged one when the motor is gradually going out of service. My views on the AKA and their rules can be said in one short sentence and are not for this place. I looked at crank savers over 10 years ago and everyone I spoke to in Australian karting thought I was nuts and refused to entertain the idea.

Bruce, from memory, the Suzuki (early models LJ10/20/50) two strokes had roller bearings in about the size you are looking for.
Kryn

I have another complete engine that has a chromed crank that was built by a very reputable Vic engine builder, I have not run it on the kart as I am saving it until I get more time in the seat. My engine I run now has a nice barrel, should probably put a fresh ring in. I have made it electric start by machining up some parts, it has a Rotax ring gear and a starter from an Italian Radne parasail motor.
The repairing of the KT cranks is more for my enjoyment and tinkering factor, at some stage my friends are going to need rebuilds, none of them are really mechanically adept apart from kart maintenance, which some are questionable at.

Bruce

Originally Posted by KBs PensNmore

Bruce, from memory, the Suzuki (early models LJ10/20/50) two strokes had roller bearings in about the size you are looking for.Kryn

Good luck finding bearings for them!

Bruce can you please tell me who does your hard chroming?

Jordan, hard chroming isn't suitable if used as a bearing race with needle bearings. As you mentioned it flakes. It is however perfect for plain bearings or bushings.

Pete

Hi Pete,
I tried to track down the actual hard chroming business that was being used but could only get the suburb as the engine builders tend to keep it a secret, they charge varying amounts.
From what I can recall Peter Woodgate from Woodgate racing charges I think $140 a half, he mentioned that when he has a few cranks he sends them off as a batch to make it profitable. if you are looking to have something done other that a crank he may pass on the info to you.

Regards
Bruce

Originally Posted by argeng

Hi Pete,I tried to track down the actual hard chroming business that was being used but could only get the suburb as the engine builders tend to keep it a secret, they charge varying amounts.From what I can recall Peter Woodgate from Woodgate racing charges I think $140 a half, he mentioned that when he has a few cranks he sends them off as a batch to make it profitable. if you are looking to have something done other that a crank he may pass on the info to you.RegardsBruce

I suspect RAD hard chroming up here in brizzy might be a usefull mob for you - they charge $300ish for a grind back/chrome/grind to final diameter for fork tubes - i suspect they do all manner of hard chroming work though.

There are three well established hard chrome platers in Melbourne its the grinder you need to find unless you have one

Step1 undercut the crank 0.25 mm mm on Radius

Step 2 have the Plater mask the crank and plate to a depth of 0.30 -0.35 mm

Step 3 Grind the Crank to Size paying particular care not to crash the corner radius

Australian Surface Tecnolgies
http://ast.net.au/

Hardchrome engineering
http://www.hardchrome.com.au/

Carroll Plating
http://www.carrollelectro.com.au/contact-us.htm

Grinding etc

Sothern Grinding etc

Good luck with It Bruce

Ok thanks, I'll follow up those links. Someone in Sydney would be better, but the parts are small enough to freight if required.

RAD do the grinding too - I'd give them a buzz as a one stop shop.