Author Topic: Well....This explains a lot!  (Read 17084 times)

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Offline slawsonb

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Re: Well....This explains a lot!
« Reply #20 on: February 18, 2015, 05:36:21 PM »
In my distant recollection, Probably 1975, I recall talking to a guy at Rockford Motors prior to sending my crank there for rebuild (all new bearings including big ends and laborynth). He explained that they had a set of jigs they used to do this overhaul, and while I'm not conversant on the details of these pieces, couldn't the steel spacer used on your Kawasaki crank be replaced by an assembly jig that controlled the depth of press and therefore the spacing?
...bert

Offline Gerrit

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Re: Well....This explains a lot!
« Reply #21 on: February 18, 2015, 08:27:20 PM »
There's a drawing on page 40 of the Rockford Motors service manual which shows the crankshaft oiling system. Interestingly, the female inner flywheel in the drawing shows a bevel on the edge of the hole where the spigot of the male inner flywheel enters, plus a generous radius (or fillet) where the spigot joins the 30 mm mainshaft on the male inner flywheel. Even more interesting is that the top photo of Sye's flywheels (first post in the "Is this crank usable?" topic) shows this bevel, which is clearly lacking in the photo in monpup's first post in this topic. It's hard to tell whether Sye's male flywheel has the large fillet from the photo, however- judging from the top photo it doesn't.
Could the female flywheel with the bevel be a later, modified part, I wonder. My engine has the number 06213, so hopefully it has a beveled female flywheel and a filleted male flywheel- though there's no guarantee that the crank is the original fitted to the engine in the factory.

Offline disc_valve

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Re: Well....This explains a lot!
« Reply #22 on: February 19, 2015, 07:12:14 AM »
About 30 years back, I had one ignition coil fail on my 175 while out for a ride. With no way of fixing it at the side of the road, I rode home (around 70 miles) on one cylinder. The bike was a bit underpowered and over-geared on on e pot, making pulling away from junctions and traffic lights a bit interesting, but it made it home and fired up first kick once I'd fitted another coil. It's probably just as well I didn't know about the weak crank at the time, otherwise I'd have been a bit worried - but the bike is still running well on the same crank some 15,000 miles later.

It m ay be that the crank break depends on which pot has stopped firing - I think it was the left pot on  mine that went. if the left isn't working, there will be no power pulses running through the crank centre. If it the right hand pot that has failed, the "good" left hand pot will be driving through the crank centre a right hand crank to reach the primary gear. Maybe thatgives more dynamic load and torsional vibration? Food for thought.

In any case, I seem to have got away with it once!

Offline bsracer

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Re: Well....This explains a lot!
« Reply #23 on: February 20, 2015, 04:59:36 AM »
Hi Gerrit,

In the bottom picture of my reply #13 there is a small dimple in the very bottom of the photo. The same dimple can be seen in Moonpup's photo at the beginning of this post. I looked at several 175 cranks and there are dimples opposite each other on the inside of both center crank wheels. I have seen where spacers with the correct distance for the center width are made when rebuilding a twin crank. I'm assuming that when Bridgestone assembled cranks at the factory they must have had some sort of jig that a spacer was put between the centers and pressed with enough force to get proper distance and leave the dimples.

paul

Offline moonpup

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Re: Well....This explains a lot!
« Reply #24 on: February 20, 2015, 07:43:30 PM »
Cranks with dimples.... scheeeesh, no wonder they had weak shafts!  ;D
Confucius say... "Better to have Bridgestone than Kidneystone"

Offline Gerrit

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Re: Well....This explains a lot!
« Reply #25 on: February 21, 2015, 05:59:45 AM »
A quick rough measurement indicates that the distance between the inner flywheels of an assembled GTR crankshaft is about 50 mm, give or take a few tenths. Subtracting the thickness of two shims and the width of two main bearings indicates that a spacer would have to be about 17.4 mm long, but at least 0.05 mm longer than the width of the lab seal to prevent the seal putting a side load on outer races of the inner mains. Bearing companies such as SKF can supply ground steel sleeves with an ID of 30 and an OD of 35 mm, which can be machined to the correct length. This does mean either modifying the standard lab seal or making a new one, but this is a minor matter.
In any case it is the route I'll be using when I get to having my crankshaft rebuilt. No doubt Rockford had a special tool to keep the inner flywheeels at the correct distance, but this is not available to us mere mortals.
Regarding the part numbers for the individual flywheels, Kawasaki didn't mention the part numbers in the parts catalogues for the Triples (though they are mentioned for the Twins in the Great A1 and A7 parts catalogue!), but they were available to dealers in separate documents. So the same probably applies to the GTR and DT. Now to get hold of this info......

Offline davis

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Re: Well....This explains a lot!
« Reply #26 on: February 23, 2015, 08:46:14 AM »
Perhaps I'm wrong, but moonpup's crank pin shear appears to be at the solid end, not at the smaller diameter pressed end. If so, why would it fail at the larger diameter? Possibly the stress is dampened on the pressed joint by a slip of the fit, which in itself would induce greater vibration. Perhaps this is why this problem comes up when running on one cylinder, causing a small slip from the uneven torsional load on the crank shaft. Also, it seems apparent that engine frame support is cracking at its weakest point. Could a slip cause an added vibration not objectional enough to be looked at but enough with time to cause crank pin and/or mounting bracket fatique? It would be interesting for the crank rebuilders to look at the trueness of their alignments before disassembly. I think I would look at using the approiate Locktite for reassembly if it is not already done.

Any thoughts on this?

Offline bsracer

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Re: Well....This explains a lot!
« Reply #27 on: February 26, 2015, 10:57:04 AM »
I talked to the guy who ported my cylinders. He has two cranks that were for Don Vesco's 350s. He said they're wrapped up and in excellent shape. He said he's want $350 per crank if anyone is interested.

paul

Offline farmerdl

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Re: Well....This explains a lot!
« Reply #28 on: February 26, 2015, 11:09:19 AM »
I'd take them in a heartbeat.  Let me know where to contact him.

Offline bsracer

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Re: Well....This explains a lot!
« Reply #29 on: February 26, 2015, 12:16:23 PM »
Sye already asked about one crank, so I guess you got dibs on the other. I need to get Sye a quote for shipping to the UK.


paul

Offline farmerdl

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Re: Well....This explains a lot!
« Reply #30 on: February 26, 2015, 01:59:20 PM »
Thanks,  let me know where to send the check and how much for shipping.
DL

Offline Mopar392

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Re: Well....This explains a lot!
« Reply #31 on: February 26, 2015, 03:08:48 PM »
350 bucks is a steal, that's what I paid 6 years ago for an NOS crank after mine snapped at 75 MPH, what a ride that was.

Offline BRT-GTR

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Re: Well....This explains a lot!
« Reply #32 on: February 27, 2015, 05:48:59 AM »
Paul,
         If either of those deals fall through or you find another one, can I have dibs on it.  That would put another GTR back on the road.
      Brian the Brit.

 
 
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I'm so glad I grew up in the 60s & 70s. I did so much stupid stuff and there's no record of it.............Anywhere !!

Offline slawsonb

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Re: Well....This explains a lot!
« Reply #33 on: February 27, 2015, 10:45:04 AM »
Are the Vesco crank mods detailed somewhere? On the site?
...bert

Offline Gerrit

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Re: Well....This explains a lot!
« Reply #34 on: March 01, 2015, 05:44:38 AM »
Bert, Gordon Jennings didn't modify his "Son of Secret Weapon" crankshaft; at least he didn't mention any mods though he did talk to Don Vesco abot tuning a GTR engine. Tony Murphy, however, did- he added slots to the standard conrods' big-ends and used Yamaha TR2 big-end cages and needles, though the cages require some machining as they are wider than the GTR's.
My guess is that the Vesco crankshafts would be basically standard, as the TR2 appeared for the 1969 season and Don switched to Yamahas that year.
If you would like a copy of the Tony Murphy article I can send you one.

Offline slawsonb

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Re: Well....This explains a lot!
« Reply #35 on: March 01, 2015, 11:02:56 AM »
Gerrit, I would love to read more, so if you could send that would be great. Thanks.
...bert

 


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