Potential disadvantages of basing a built 750 on an XS2 engine?

[arcticXS]

A while ago, I bought a used XS2 engine, planning to use it for my 750 rephased build.
I already have a rebuilt 533 crank, MrRiggs rephased Shell#1 cam, "big fin" 750 cylinder block, and Wossner pistons for this build.

Is there anything different with regards to primary drive, clutch or gearbox that would make the XS2 a less suitable core for a "built" engine? I plan on removing the electric starter, so that will not be a potential issue.

 

[MaxPete]

I hate to speak on this because I may be quite incorrect - BUT I will out of an abundance of caution. There are two points which may impinge on this question:

1) At least some of the earlier engines (up to 1973 I think) had a different number of teeth and a different chain pitch on the timing chain (i.e. camshaft) drive.

As I am sure everyone is aware, ALL four-stroke cycle engines require a 1:2 ratio between the crankshaft and camshaft and so having a different number of teeth on the crankshaft sprocket means that you cannot mix "old" and "new" camshafts and crankshafts.

2) I believe that some of the early generation engines had a needle roller bearing at the small end of the connecting rod (like one would find in a two-stroke cycle engine) and this resulted in a slightly less robust small end because the needle roller bearing is a fairly bulky. Later con-rods had a beefier small end once Yamaha eliminated the needle roller bearing and went to a bronze bushing - which seems to virtually never fail.

....just my $0.02 (which is around 1.56 cents USD at the present rate of exchange).

Pete

 

[grizld1]

Pete, needle bearings were found only in very early XS1 small ends; Yamaha went to solid wristpins before the first half of the model year was out. Arctic is using a 533 Euro crank and has the knowledge and experience to use a compatible chain and cam sprocket.

Bottom line, arctic: no worries. XS2 cases are the same as later 447 and 533 cases and trannies, up to the very minor 1978 transmission change, and you can even stick a late tranny in those cases if you wish (though I have no idea why you'd want to). The clutch and primary are the same as 447 units up to 1980 as well, and again, you can swap in the late stuff, but I see no reason to do so. Sounds like you have the makings of one fine motor!

 

[grizld1]

Clarification, arctic: the clutch hub and primary are the same, some difference in early friction plates. You'll probably want to use some nice friction plates from Ferodo anyway!

 

[MaxPete]

Pete, needle bearings were found only in very early XS1 small ends; Yamaha went to solid wristpins before the first half of the model year was out. Arctic is using a 533 Euro crank and has the knowledge and experience to use a compatible chain and cam sprocket.

Bottom line, arctic: no worries. XS2 cases are the same as later 447 and 533 cases and trannies, up to the very minor 1978 transmission change, and you can even stick a late tranny in those cases if you wish (though I have no idea why you'd want to). The clutch and primary are the same as 447 units up to 1980 as well, and again, you can swap in the late stuff, but I see no reason to do so. Sounds like you have the makings of one fine motor!

Good info - thanks Dick!

Pete

 

[GLJ]

72 cases are not as robust as later cases they are a bit weak at the upper rear motor mount. They have been known to crack.

 

[650Skull]

Scroll down about a 1/4 of the page..........Shows the difference in the factory strengthening around the rear engine mount, on the 70-72 case to the 74-83 case...........if the cases are apart the 72 case ribbing could be strengthened by building up the ribs
http://www.xs650.org.au/Club Racer Stuff/Club Racer 2017.htm

 

[TwoManyXS1Bs]

The XS2 and 447 cases will have crank squirters for the slotted big ends, shouldn't hurt the 533 "scooped oiling" crank.

http://www.xs650.com/threads/anyone-ever-see-this-before.37327/page-2#post-375597
http://www.xs650.com/threads/extra-oil-gallery-jets-only-to-the-lh-side-why.37362/
http://www.xs650.com/threads/small-ends-and-the-oil-jets.44130/

Recommend using the later 74-up clutch, which has better internal oiling, and the splined mating of the pressure plate to the hub. Avoid the older 70-73 thicker 6-plate clutchpack. The older basket can be used, but may be quite used up.

Posts #7 and #14.
http://www.xs650.com/threads/xs1-clutch-recommendations.51409/#post-539384

Post #51.
http://www.xs650.com/threads/yamaha-xs650-experimental-clutch-version-2-0.50189/page-3#post-530963

 

[grizld1]

Thanks, 2M. I knew the basket/primary gear was the same, assumed hub and pressure plate were as well. And yes, I know why one should never assume....