Short Stroke 750 Build

Status
Not open for further replies.
YOU'RE GETTING CHIPS ON THE BLOODY YAMAHA!

Doggone it, cover it up, man!

What a neat looking little bike...
 
splatt said:
Thanks for the intresting thread, I'm curious as to what you actually are using as a set up register, as you appear to have turned and bored the sleeve in two steps, and you have removed the case from it's original set up, I suppose my question really is how are you keeping the tunnels in line, :?:
Click to expand...

My uneducated guess is that the cases will go back together for the final bore?
 
Dave,

in this case I just leveled the case using a dial indicator mounted on the quill, and centered on the bearing bore. Since the sleeve is concentric, all I have to do is repeat the process for the final boring.

When I first set up these cases back in the '80s, I had to bore the main bearing boss after welding, because welding the reinforcing plate around the seal area had shrunk the bearing bore when the weld cooled. At that time, I set up the timing side and indicated off the dowel pins to find the coordinates of the bore in the timing side, then did the same with the drive side and bored it to match. Since I already know the bearing bores are in line, all I have to do for this operation is indicate on the existing bore to find the center.

It would be nice to be able to line bore with the cases together, but that would involve making more tooling, and my current method should keep the bearing bores in line within .001" or so, which well within the mis-alignment specs for these bearings.

Ken
 
More progress. The bronze sleeve in the drive side case half is finished. Pictures below show details.

Boring the sleeve in my worn out 20 year old Taiwan mill. Light cuts and slow feeds, but still working.

Short Stroke 750 Build


Cutting the relief for the hardened anti-rotation washer.

Short Stroke 750 Build


The finished sleeve installation.

Short Stroke 750 Build


Next step is Timeserts in case.

Ken
 
swooshdave said:
How much of the sleeve was left? Look like it's about half the thickness it was.
Click to expand...

.084" thick when finished. I could have made it thinner to start, but if I try to make it too thin in the lathe, it tends to be not so round. Easier to make it a bit thick, and just bore it more in the mill. I've also seen the repair done with a steel sleeve shrunk onto the bearing race, and then the whole thing shrunk into the case, which is bored to fit. That would be harder for me, because of the retaining washer. Besides, I like using bronze, because it has a thermal expansion coefficient in between aluminum and steel, and I think that helps keep the fit tight. Just my personal preference.

Ken
 
Finally, a little more progress. I machined the timing side for a retainer to prevent the main bearing from rotating, similar to the one alrady in the drive side.

This is a shot of the retainer during a trial fit before installing the bearing.

Short Stroke 750 Build


I also finished installing Timeserts on the threaded holes for the cylinder studs and through bolts. I like the Timeserts better than helicoils for really high stress areas. I use helicoils in other areas, but for cylinder (and head) fasteners, I prefer the Timeserts.

Short Stroke 750 Build


Next step is deciding on breather design. I've always used the stock system on my race bikes, but I'm really intrigued by the CNW kit developed by Jim Comstock. I've got a couple different small reed valves, and I might make my own along the same lines.

Ken
 
Thanks for the pics. What kind of cost are timeserts? Seems like something that would be worth while keeping a stock of.
 
In the 3/8-16 size, the kit, which includes drill, counterbore, tap, and insertion/licking tool, with 5 or 6 inserts, is around US$50.00. The inserts, which are available in a wide variety of lengths, are around US$1 each.

Lots of info at www.timesert.com. I buy them from Pendergrass Tool, www.pendergrasstool.com, who stocks all the sizes. He's only a few miles from me, so I pick them up from him directly, but he ships all over.

Ken
 
Finally, some more progress. I'm finding it difficult to have the time to work on it, and everything naturally takes much longer than I expect. After reading all the posts about reed valve breathers, particularly Jim Comstock's dyno experiments, I've decided to try one. Jin was kind enough to say he didn't mind us copying his work, so I decided to do my version, using a reed valve from the eBay source Jeandr posted. It's finished, except for cutting some gaskets. Next step is to plug the holes in the timing side, and drill a new drain hole at the bottom, near the oil pump.

Short Stroke 750 Build


Short Stroke 750 Build


Ken
 
Short Stroke 750 Build


Hi Ken, very nice welding job! I wonder did you take any precautions to prevent the case from deforming during welding?
After heating up and welding mine there was a little gap where the two halves come together at the welding spot. Not big enough to give any trouble but I had to bolt the halves together with some force to close this gap. Anyway I like to know if there is a more gentle way to cope with this deforming matter.
Thanx

Short Stroke 750 Build
 
nortonspeed said:
Hi Ken, very nice welding job! I wonder did you take any precautions to prevent the case from deforming during welding?
After heating up and welding mine there was a little gap where the two halves come together at the welding spot. Not big enough to give any trouble but I had to bolt the halves together with some force to close this gap. Anyway I like to know if there is a more gentle way to cope with this deforming matter.
Thanx
Click to expand...

Thanks for the compliment, but I have to give the credit to the welder I used to take this sort of work to back in the '70s. He was really skilled. I do my own welding now, but I'm still not up to his level. I bolted the case halves together before taking them to him, and he preheated them before starting the welds. It still distorted enough that I use Locktite Master Gasket on the mating surfaces, because it will fill larger gaps than the usual case sealants. I also had to re-machine the main bearing bore, which shrunk a bit from welding on the reinforcing plate.

Ken
 
It shouldn't be to hard to put a 1/2 bearing shell on just the bottom side of the cam in the middle. weld, bolt on bronze & line bore/ream.
Jim Schmidt
 
jseng1 said:
It shouldn't be to hard to put a 1/2 bearing shell on just the bottom side of the cam in the middle. weld, bolt on bronze & line bore/ream.
Jim Schmidt
Click to expand...

A good idea for a future build. I wonder if that would let us use an even crazier lift profile.

Ken
 
A little more progress the last few days. I installed new main bearings, with a .005" shim behind the timing side bearing in the case to get a little under .010" end play in the crank. Once I was happy with that, I ground the notches in the outer races for the retaining washers I use. This is a shot of the setup I use for grinding the notche in the race.

Short Stroke 750 Build


This is a shot of the finished counterbore, ready for the washer and retaining screw.

Short Stroke 750 Build


I also plugged the holes in the timing side with aluminum pipe plugs, and tapped the old breather pipe hole for a 3/8" pipe plug.

Next step is a little cleaning and then painting the cases. I haven't painted them in the past, but after seeing the results of the Old Britts technique, I'm going to give it a try. I used to see case painting as a waste for a race bike, but now I'm older and mellower, and a bit more interested in cosmetics.
 
Hi , is it necessary to weld that reinforcing plate , or could we put it around the bearing boss with an interference fit???
and/or fit an "old" bearing in both cases to limit the warpage, or more radically fit the crankshaft in and bolt the cases ??
 
Maney case would weight more than modified Combat cases.
If you weld another bolt-bolt plate on the TS half then ya can drill and place an 11th clamp bolt in that weep prone seam section. I closed my weld distorted gap by time proven brutal beating on welds, a lot. I used a room heater size pancake
LPG burner to get cases with barrel attached at least 500'F or more to burn off oil in pores and any carbon.Acetylene torch soot stain should burn off when Al is ripe to weld.
Combat oil pick up needs move to rear if not already done.

You might consider dealing the the remaining stress risers I still see in the sharp corners next to the through bolt mount bosses. Grind out fill in Al bead then
grind to radius corner. My Combat cases were found crack in these spots not the upper half you've dealt with so far.

I had my cradle/cases re-drilled for interference fit air craft grade 8+ 7/16" fasteners.

Ken placed Timserts in every possible case thread of Peel project, for preventive strength and less wear taking apart and back together a lot.

hobot
 
Seeley920 said:
or just buy a set of Maney cases!!!
Click to expand...

Agreed. I like and use Steve's cases. For this engine, I already had the cases, which I had modified years ago. All they really needed for this build was sleeving the bearing race, and machining for the anti-rotation washers. All that cost was my time, and not too much of that, so it didn't seem to me to justify the cost of another set of Steve's cases.

Ken
 
marinatlas said:
Hi , is it necessary to weld that reinforcing plate , or could we put it around the bearing boss with an interference fit???
and/or fit an "old" bearing in both cases to limit the warpage, or more radically fit the crankshaft in and bolt the cases ??
Click to expand...

I don't know about shrinking on a reinforcing ring. I thought about it, but never tried it. I considered the reinforcing ribs at the rear to be essential, so the cases were already being welded, and it seemed reasonable to weld the reinforcing plate as well at the same time.

I did try welding a set with bearing races installed, and it didn't work out too well. The heat of welding let the material around the races expand, and when the cases cooled, the races stopped them from shrinking back to the original size. The result was a loose bearing bore.

I put a lot more time and effort into the race engines back then. Nobody was making aftermarket cases back in those days, so we pretty much had to do this sort of modification. Nowdays, I'd just do as Seeley920 said, and buy a set of cases from Steve.

Ken
 
Status
Not open for further replies.
Back
Top