G1 primary clutch retaining bolt

[mikeasis]

Anyone know the primary clutch retaining bolt size and thread pitch. Im needing to clean the crank threads and Im getting lost here. Ive got a new OE bolt so I checked it and I keep coming up with 1/2 x 20 on it, Im pretty sure its supposed to be metric.

Yamaha part #JN7-46249-00

[cgtech]

Definitely metric

[Field6565]

You are correct Mike. 1/2 X 20 is the bolt size. I know this because when first put a clone in my G1 I had to drill and tap the clone crank to fit the original clutch bolt and clutch

[mikeasis]

I have the thread pitch checkers (look like little combs) and I checked like 5 times and none of the metric pitches fit quit right, then took it and stuck it in a check a bolt/thread at the work, I really wouldn't have thought that it would be standard threads but it is. I took a primary bolt out of another engine and verified that it is indeed 1/2 x20.

Now if I can find my case bolts Ill be back in business.

[cgtech]

Wow, never seen any parts made by Yamaha use SAE threads. Not counting the Dana or TEAM axles made in the US for Yamaha. Surely not saying you guys are wrong, just shocked.... Guess I never needed to spec-out that bolt.

[Field6565]

Originally Posted by cgtech

Wow, never seen any parts made by Yamaha use SAE threads. Not counting the Dana or TEAM axles made in the US for Yamaha. Surely not saying you guys are wrong, just shocked.... Guess I never needed to spec-out that bolt.

I was quite surprised myself.

[Magnum61]

I sent my 86 g1 motor out for a rebuild by a certified Yamaha tech. It came back and I couldn’t get the primary clutch bolt to thread into the crankshaft. The old bolt, taken off before the rebuild is a 1/2”-20 thread. I got the new crankshaft thread roughly measured as M12x1.25. Ordered a bolt, it threads into the crankshaft easily and doesn’t jam, but bolt seems loose when threaded in. The tech said the crank he used had the oem yamaha part number on it. Has anybody encountered a smaller hole in the crank, and what size is it, or being these cranks have been discontinued, could they have been superceded by a crankshaft from a different machine, ie. snowmobile?

[Magnum61]

Do you know what size?

[mikeasis]

Originally Posted by Magnum61

I sent my 86 g1 motor out for a rebuild by a certified Yamaha tech. It came back and I couldn’t get the primary clutch bolt to thread into the crankshaft. The old bolt, taken off before the rebuild is a 1/2”-20 thread. I got the new crankshaft thread roughly measured as M12x1.25. Ordered a bolt, it threads into the crankshaft easily and doesn’t jam, but bolt seems loose when threaded in. The tech said the crank he used had the oem yamaha part number on it. Has anybody encountered a smaller hole in the crank, and what size is it, or being these cranks have been discontinued, could they have been superceded by a crankshaft from a different machine, ie. snowmobile?

the G1 engine IS a 250 enticer engine detuned. the engine cases are the same part number as well as 3 of the pieces of the crank shaft. the clutch side of the enticer is longer and has a different part number

if you bought the crankshaft from a Yamaha dealer and they cant provide a bolt that properly fits then it needs warrantied. PERIOD
Im willing to bet theyve sold you an aftermarket crank with **** threads as the OE cranks are no longer available