1974 Yamaha MX360

Brid Caveney 12/8/2017 1:23pm
12/8/2017 1:23pm Edited Date/Time 12/9/2017 3:51pm
High all -- we are a small shop in Austin TX, West Coast Racing, specializing in Custom builds - on Vintage bikes - both street & competition. We have 2 1974 MX360's in right now, for race prep. First one, the barrel was badly scored, so it is on its way to LA Sleeve for a new sleeve and boring for a + 0.25 RT2 piston (it was at 1mm over), that came with the bike (only recently bought by customer) we sort of assumed that piston was correct -- but, can any confirm that please?
It also needs crank seals, and on pulling the clutch side case off, we find a LOT of slack in the crank balancer chain -- is this normal? Don't have a manual for the bikes - so, just going by 'feel'!! Will also need to be knowing what the piston ring gap should be, when we get the barrel back.
Cheers,
Brid.
PS -- Facebook page is www.facebook.com/westcoastracingvintage

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Brid Caveney 12/8/2017 3:39pm
12/8/2017 3:39pm
Also found this piece of hard plastic, wedged behind the balance shaft sprocket -- any ideas where it came from?

FGR01
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FGR01 12/8/2017 10:00pm
12/8/2017 10:00pm
I'm guessing the block of plastic is a chain tensioner that fell out of place and that is why the chain is so loose.
Brid Caveney 12/9/2017 11:47am
12/9/2017 11:47am
FGR01 wrote:
I'm guessing the block of plastic is a chain tensioner that fell out of place and that is why the chain is so loose.
No tensioner on it FGR01! The block is just a guide - and the 'stray' piece of plastic did NOT come off it.
Anyway -- not that bothered really -- BUT, we now get to the crank seals - and spring orientation on them? The existing ones have the spring facing out - both sides (but are hardly likely to be OEM ones)
mx317
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mx317 12/9/2017 3:36pm
12/9/2017 3:36pm
Looks too loose.

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project racer 12/9/2017 3:36pm
12/9/2017 3:36pm Edited Date/Time 12/9/2017 3:51pm
I removed the counter balance garbage on my 74 MX360 Champion. As one of the heaviest two stroke engines Yamaha ever produced, it won't miss the weight. I did have Falicon rebuild and rebalance the crank, though.Kind of a turd engine ,IMO.

Springs facing out is correct on the seals. The spring creates a bit of tension to seal around the crank ends. Also, if a spring were to pop off or break, it does not get sucked into the main bearings, chomped to bits, and leaving it's autograph your nice new cylinder sleeve.

Brid Caveney 12/9/2017 4:05pm
12/9/2017 4:05pm
Nice thing about the champion frame is - you can put a lot of different engines in there!!
Yup - we removed the counter balance mech, but on the springs -- clutch side is spring out, but mag side - spring in. We'll take our chances on that one - hehe! I once owned a Rotax 600 single (& single cam) RR bike, with a Terry Knight frame. Few folks know that, although Terry was well known for his DT frames, he did a short run of RR ones. It handled like a dream! Thanks for the advice -- looks like we're 90% with you.

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