Author Topic: YD1 historical tech query  (Read 224 times)

0 Members and 1 Guest are viewing this topic.

Offline Bluehaze

  • Back Lane Scratcher
  • Posts: 102
  • Location: Australia
YD1 historical tech query
« on: August 30, 2019, 02:16:17 AM »
Not RD, but I have a question regarding the first Yamaha twin.
The 250 YD1 design was reportedly bought from Adler when they stopped making motorbikes.
Adler had an interesting way of making their engine - not split but a "tunnel" design.
The YD1 looks similar from the outside.
But, did it also use that method, or did they change it to a split case from the beginning?

Offline tractorman

  • Club Member
  • Port Hacker
  • Posts: 1361
  • Location: Andover, Hants
Re: YD1 historical tech query
« Reply #1 on: August 30, 2019, 01:39:30 PM »
Steve Cooper in CMM Mechanics has one in this months magazine he's going to strip down. Looking at the photos it isn't horizontally split but cant see if its vertically split.

Offline Bluehaze

  • Back Lane Scratcher
  • Posts: 102
  • Location: Australia
Re: YD1 historical tech query
« Reply #2 on: August 30, 2019, 02:07:10 PM »
Thanks tractorman.
Is a YD1 engine stripdown going to feature in an upcoming issue of Classic Motorcycle Mechanics?
It's not a magazine I see for sale where I live.
If an article does appear, please let us know.

Offline tractorman

  • Club Member
  • Port Hacker
  • Posts: 1361
  • Location: Andover, Hants
Re: YD1 historical tech query
« Reply #3 on: August 30, 2019, 05:04:56 PM »
From reading the first instalment I would say yes.

Offline Bluehaze

  • Back Lane Scratcher
  • Posts: 102
  • Location: Australia
Re: YD1 historical tech query
« Reply #4 on: September 06, 2019, 11:49:18 PM »
Here's the Adler MB250 crankshaft, showing the serrated joint.
Has this been seen on any Yamaha twin?

Online 5port

  • Club Member
  • Port Hacker
  • Posts: 7974
Re: YD1 historical tech query
« Reply #5 on: September 07, 2019, 07:53:31 PM »
That is a good pic Bluehaze!  Can you post more?  It is obvious where a lot of features come from, look at those slotted rods!  As far as the serrated coupling, hmmm there might be others but, I think they will have been similar vintage?  The more recent version I recall of a coupled crank twin is the 5F7 TZ250 about 1981 that has what is really a two-part crank coupled in the middle by what is really a large diameter spline, with shallow engagement.  Cheers

5port
5port

Offline Bluehaze

  • Back Lane Scratcher
  • Posts: 102
  • Location: Australia
Re: YD1 historical tech query
« Reply #6 on: September 08, 2019, 12:35:08 AM »
This is not my bike unfortunately.
The serrated joint is known as a Hirth coupling.
The method of tightening with the special tool is interesting, using a bolt with a "gear-head", necessary for access to enable engine disassembly.
The design allows a single main crankcase casting.
My guess is that Yamaha revised it for the YD1, splitting the case vertically and using a pressed-together crankshaft.
That's how I've seen it on other pre- YDS7 twin engines, but wondered about the first Yam twin with the pressed steel frame - maybe for the one model they followed the Adler system?
There are a few photos of the YD1 online, but I can't find any detailed factory literature.

Another feature that was used on some early Yamahas is the engine-speed clutch.
Spinning the clutch faster allows for a lighter clutch hand-lever action.

Regarding other methods of coupling crankshafts, I think the way it was done on 4 cylinder Yamaha racers was neat: They took the drive from between the two "twin cylinder" shafts that each had a gear on their ends. These engaged with another gear of twice the length. Search for "TZ750 engine" for pics.
« Last Edit: September 08, 2019, 08:39:46 AM by Bluehaze »

Online 5port

  • Club Member
  • Port Hacker
  • Posts: 7974
Re: YD1 historical tech query
« Reply #7 on: September 08, 2019, 07:03:36 PM »
Thanks for those pics!  Yes, very Germanic.  The Hirth coupling and toothed-drive fasteners are interesting, very 40's tech. I do think Yamaha progressed this very well.  The crank-end clutch was another tech that had it's time.  Yes, theoretical weight saving but, that is lost when you factor in the strength that the clutch needs to operate at 9,000rpm.  Didn't work that well in practice and the Yamaha's with crank end clutch had problems.  Far better was the 3,000rpm clutch after the primary gears, can have light alloy basket/drum construction and, piggyback the large primary gear that has to be strong anyway.  ;)
Yes, the TZ750 is neat but, cranks not coupled as such, just sharing the layshaft gear with individual crank gears.  I think the Suzy RG500 is also mechanically similar with four discvalve 125's driving a common layshaft in the middle.   Cheers

5port












     
5port

Offline Bluehaze

  • Back Lane Scratcher
  • Posts: 102
  • Location: Australia
Re: YD1 historical tech query
« Reply #8 on: September 09, 2019, 12:02:36 AM »
That's right about the engine speed clutch needing to be stronger, also probably better balanced.
They had a reputation for being harsher in action, but I didn't notice it on my MZ ETZ250. They had them until end of production in 1993.
Likely they are not popular because of more weight and expense, for little gain.

Aside: I met another MZ owner who said he didn't trust the East German oil pump, so ran his on premix.
I pointed out that the pump was Mikuni, made in Japan.
It also had a Brembo disc brake.