1970 Engines

[Jasonbobb]

I went picking today and baught some disassembled motors and some extra parts. The gentlemen told me that one of the engines is an 1970 and one of the most sought after engines because of the stroke and the cam that is in it. Is this true or was he blowin smoke up my tailpipe? I bought everything anyway and will be letting a bunch of it go as I don't need all of it. He did have a complete pamcopete kit and a sweet exhaust system for my bike, I was happy about that. Thankyou Jason

 

[Jasonbobb]

Ok I've been searching the forums like crazy,,lol,,found out that he wAsmt bs'n me. Then I found a vin search PDF and I found out that not only is the engine I picked an xs1 the motor in my current project is too. It's coletwly stock. Sorry forms ting. I should've just done sum more research.

 

[gggGary]

The early engines have good and not so good features. Real early 70 engines have roller small end rod bearings. Oops not such a good idea for a 4 stroke. Yeah the early cams are supposed to be "hotter" but not quite as 'streetable' It's a bit harder to find early engine parts,so more $$. The left exhaust valve cover being three bolt and no E start gear box under the drive sprocket are the fast ID for 70-71 engines. The 256 engines use a 22mm small end rod journal and under hard use it can stretch so that's a minus. The later engines went down to 20mm allowing more beef around it.

Probably the biggie is "real" XS650 nuts will notice the 3 bolt LH valve cover.

 

[yamasarus]

The 70 cylinder head had noise suppressors between the fins. That's a dead giveaway for a correct 70 engine. The needle bearing top end was changed mid production in 1970. When that bearing failed it could destroy the engine, even putting the rod through the case, so if you have needle bearings change it right away.

 

[XSLeo]

The stroke was the same on all years, 74 mm. The early 256 engines used a longer rod with a shorter piston. This extended the dwell time at the TDC position.
The cams had steeper opening and closing ramps as well as different opening and closing timing.
The intake and exhaust porting was different as well.
The carbs were of a raised floor design.
All these things made the engine run a bit stronger across the rpm range. In the later models they changed things to help quiet the engine and ease maintainance. They found out with these changes the overall performance wasn't hurt much.
Leo