I have recently been helping my friend with fitting a CRF250 engine to a go kart and have recently stumbled across a slight problem that was not anticipated.

Due to the position the engine is mounted, the angle of the chain is not any use and would be catching the engine casing.

What I have started doing is making a chain guide. I have fabricated a guide , however I am looking to find out what type of plastic is used on the likes of timing chain guides????

I would suggest polycarbonate. Easily bought in sheet form. It's high impact, used in applications such as riot shields etc.

Ok could polycarbonate not be a bit brittle? I was thinking something a bit more like a very hard wearing rubbery sorta plastic.

Will have a look into polycarbonate tho thanks.

The swing arm chain blocks on all the motorbikes I’ve ever had seem to be made of a hard nylon type material . Obviously nylon is used to make bearing blocks and bushes , so it has some self lubricating properties . My last bike had 128 horses at the rear wheel and after 9000 miles the block was still serviceable. So if it was me I’d be looking at Nylon, PTFE , that sort of thing. Or make your guide in Ali and buy the swing arm guide from a Superbike to bastardise and top it shouldn’t be expensive . Ps if you use Wurth dry chain lube it keeps things very clean looking 2009 GS Auto Zermatt Silver - Sold June 21 after 10 years of ownership

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Last edited by MartynB on 10th Nov 2017 8:37 pm. Edited 1 time in total

Trav wrote:

Ok could polycarbonate not be a bit brittle? I was thinking something a bit more like a very hard wearing rubbery sorta plastic.

Will have a look into polycarbonate tho thanks.

Dippy it may be the wrong type, however it pointed my in the correct direction.... Polyurethane is what seems best however may start looking into nylon base products. Polyurethane comes in many grades some as hard as a bowling ball and is extremely scratch impact and heat resistant. Polycarbonate ticker two of the boxes however is not very scratch resistant, which would be required for a chain guide.

Was hoping too make one quite thick about 8-10mm so that it’s not regularly getting changed. Not really wanting to bastardise part to make them fit as we are wanting the kart to look finished to the highest standard and not made in someone’s garage. (Even tho it 100% has been). Will look into it all the same and see what I can come up with.

Usually Go Karts are built for specific engines, what was the original engine? does it have gears, wet or dry clutch if without gears? if dry clutch then the clutch can be reversed to give more clearance. my PC is slightly to the right of Genghis
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We just got the frame with no engine so cannot confirm what type it was. We were assured that it was just a centrifugal clutch and no gearbox. We are fitting a Honda CRF250L. This guide is 100% essential don’t think there is anyway of dancing around it unfortunately.

Think Nylon is the plastic of choice as it is very easy to source in the form of sheets and is relatively cheap as well.

Would like to thank everybody for the suggestions they came up with