3 Questions ???

[bt24]

I have 3 Questions ??? and these will be easy for yall.

1) I'm trying to figure out what year this motor is ? 5V4 000427
2) There seems to be some sort of Black powder coating on the inside of the top end, is this common?
3) #010 is stamped on the barrell, did Yamaha do this?

Photos below, I hope they come out.
Thanks,
Bryan

 

[Sparky100]

It's an 81-82 year motor, in the tech section at the top of the page there is a chart that will tell you this info. I can't answer your last two questions, I'm sure someone else can.

 

[angus67]

your engine has been bored next size up.
Dont know about the black in the head. mine's a 1980, and didnt have that.
the engine number id is also the vin on the frame the engine belonged to. 81-83 heritage.

 

[hmusket]

Just looked at the '82 head I have sitting in front of me, black on the inside, then on the cylinder sleeves has 016, stamped on it. So angus67, you're saying that number relates to a rebore size?

 

[angus67]

yes......been known to be wrong though.
they usually go up in tenths, are you sure? maybe the stamp ink smudged.

 

[hmusket]

Clearly 016 on both. Never really paid attention to it before bt24 asked his questions.

 

[angus67]

hmmmm. dunno.
5twins should be here soon

 

[scabber]

It is the factory bore size the number 75 mm - the number etched on the cylinders equals bore size ' Yamaha matched pistons to the bore. The number on the top of the factory pistons is 74mm plus the number stamped. Subtract piston number from bore number gives piston clearance factory

 

[angus67]

so now i know.

 

[bt24]

I must have missed it on the chart. I saw the 447s but I didn't see any of them that had the#427. I'll look again.

Thanks,
Bryan

 

[bt24]

 

[XSLeo]

#1 You got an answer.
#2 This is a coating to help oil drain out of the rocker box. It also seals any possible pourosity the rocker boxes might have. Used on lots of engine very common.
#3 On page 96 of the Clymer book start reading at paragraph 5. It talks about how to measure piston and bore sizes and how to compute clearance. It explians what the numbers on the pistons and sleeves mean.
scabber has it almost right. When pistons are made they don't all come out the same size. THey measure and mark the pistons. They then match the pistons by weight and size. They then bore the cylinders to match the pistons. Then they mark the sleeves for size.
These numbers only apply when the engine is new. At this point your pistons and cylinders are worn, enough to need a bore? Only measuring can tell.
Leo

 

[bt24]

Thank you all for your knowledge and quick replies.

Bryan