Groove on Sachs crankshaft???

[Gary Roach]

This is one of those rare Sachs 1751/6A bottom ends. I was disassembling it, and when I removed the pinion gear, I noticed a groove on the crankshaft. I first thought that it was a crack, but after further inspection, I realized it's not. When you look at it through a magnifying glass, you can that the groove is perfect, so it either has to have been machined in, or casted in. I looked inside of the pinion gear, but it has a smooth bore just like the 100/125 motors have. I was hoping that someone could enlighted me on what the purpose of it is.















Gary

[Daniel P. McEntee]

I'm gonna guess that it's just a flaw in the original forging that didn't clean up in the final machining processes. If production was winding down on this engine, the crank may have come from the "it's flawed but ok,so we'll use it if we have to" shelf to help complete the run of engines.If it was a journal that ran in a brass bushing,  I would have said it was for lubrication purposes. If it was a purposeful addition to the finish of the crank shaft, I can't think of any way you could do that by machine, and I don't think CNC technology was around at that time. Interesting.
  Merry Christmas and Happy New Year!
   Dan McEntee

[Paul Danik]

Hi Gary,

   Not sure about that grove, but I do have a question about that engine you may be able to answer.

What I am curious about is the size of the liner in that engine.  I have a NOS Sachs liner and am not sure what it is for.  A local Sachs expert is thinking it is for that engine. If you could give me an OD and ID measurement of the liner, and the length as well, I would sure appreciate it.  The part # on the liner is hard to read but it looks like 0611 113 000.

PS...   Is there a key way cut into that crank for the pinion, I can't tell from the pictures? If not possibly it is to help hold the gear, just an observation...


Thanks,
Paul

[Gary Roach]

Hi Paul,

The pinion gear and crankshaft are both tapered, and there is no key.

The liner measures 60mm ID, 68mm OD, and 127mm length.

Gary

[Paul Danik]

Gary,

   Well it seems that " Crazy Jake " was correct, this liner and piston kit are for the Sachs 175 cc engine.

Thanks,
Paul

[thrownchain]

I believe it to be an oil groove to get oil to and from the bearing behind the gear. Too clean to be a flaw.

[ALB]

Hi Gary,
Thanks for the posting and photos. 20 years ago when I started getting involved with Penton parts, I acquired a complete 175 engine in the box. I never pulled one apart because that NOS engine was the only one that I came across. I always assumed that they were the same bottom end as the 125B with just a larger bored cylinder and head. I assume tha with it being an "A" means that it has a larger diameter crank to compensate for the larger bore.
I find it interesting that the pinion gear is a taper fit and not a straight slide-on with a woodruff key to keep it from spinning.

It also looks like the rod is bigger and longer than the 125 rod.

Alan Buehner

[Kip Kern]

Sachs 7 Speed?  I'm building a few right now.

[Daniel P. McEntee]

Did Sachs do seven speeders in this style case?I wouldn't think t here would be room. I thought all seven speeders were bath tube style cases split horizontally, like on my Herc 250 and 175?
   Merry Christmas,
   Dan McEntee

[checkcrew]

Gary, hi,

here is another neat little quirk about the 1751/ motors,
they use 12 spring clutch's stock,

i have only seen these motors in the 1975 Herc 175's,

 Dwight rode one for the factory team that year,
Vance has a couple of them, one he got from me,

regards,

Mike Gallagher, NJ.
[email protected]

[Gary Roach]

Al,
Yes, it has the larger crank, and the stroke is 61mm. The hole for the piston pin bearing is larger too. The hole in the 100/125 Sachs and 125/175 KTM rods are all 18mm, but this one is 22mm, which I think is about the same size as what's in the 250/400 KTM motors.

Kip,
Did you notice this groove on any of the 7 speed motors?

Dan,
As far as I know, all of the 7 speeds were in the new cases like you have.

Mike,
Yes, you're right, it does have the 12 spring clutch.

Gary