I went out to see my old mate (and Team Thumper supporter) Barry Johnson at the weekend. He plied me with beer on friday night, and we talked a load of old rubbish! Cheers Baz!
However, come Saturday, after a fry up, I had a look at a couple of XT600 motors he has. I wanted to measure the length of the studs in his crankcases.
The 34K motor (Jap import) has 4 studs of 31mm (case surface to top-of-thread)
The 3AJ motor (ie. "my" barrel) has 2 left hand studs of 41mm, and the RHS ("inside" the barrel) are 31mm
My 660 cases have 3x 31mm and 1x 36mm stud!
All barrel flanges are in the region of 19.5-20.5 mm deep.
The fixings for the RHS of my motor use a 12mm deep M10 nut (14mm head) and 2.2mm washer. Total depth = 20mm barrel depth + 12mm nut + 2.2 mm washer = 34-35mm
So on the RHS, I'll need studs of at least 36mm. This corresponds to the one stud which looks ok on that side.
However, on the LHS (where the the nuts go down inside the barrel, its recommended to use Yamaha "thick" washers / spacers if possible. (I'll have to ask Martin Sweet why, I didn't question it at the time!) These are 5mm thick, so the total lenth of available stud necessary is 37-38mm
So I reckon I can use 2x 36mm (visible above case) studs on the RHS and 2x 41mm (visible above case) on the LHS, with the thick washers.
I've also just checked the squish and valve-pison clearances. I think I was worrying about nothing, there an easy 2mm on the exhaust valves, and the inlet valves didn't even touch the plasticine.
On the minus side, I think some of the rockerbox and camchain tensioner threads are getting a bit tired. Will have to be careful, but may end up helicoiling them...
I'm going to have to measure the valve srpings tho. I thought on removal that the inner and outer springs were touchiing/rubbing/ or with very little clearance. Now is the time to investigate!
However, its a fairly simple fix- I just need to spend some money!! Then we can start to think about actually building it.
(And sorry for the lack of photos, I left the camera at work...)
andy
Spraying schedule 2014
10 years ago
2 comments:
I can tell you why the thick washers:
Normal-thickness washers will cave in into the softer aluminum under the pressure of the fixing torque and this will be compounded by the heat expansion of the alu, leaving you with reduced torgue.
Such washers were - still are as you can see - normal in well designed engines. My 1954 Mondial also has thicker washers for the 4 head bolts, not as thick as the ones you need due to the restricted room betwee the fins, but these are are ellipsoid in section, thicker in the middle so that they settle in flat on top.
having looked at the picture in that earlier blog, I would suggest using the same washers as on the right side - the are thick enuf. the really thick ones are in fact just spacers to get the nut high enuf to afford the wrench good purchase. So, I suggest turning your own higher nuts to regain the height necessary. Using suitable steel, of course.
Whereever possible, I wuld use "Kaylock" nuts.
[img]http://www.qualityproducts.de/images/pog_kaylock.jpg[/img]
These are 12.8 selflocking nuts without plastic inserts and they have smaller hex sizes. They were originally mean for use in the aircraft industry. One such idea application on the Yam engine is for the exhaust stud nuts.
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