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left end crank damage

  • Thread starter Thread starter rosco15
  • Start date Start date
R

rosco15

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I know the #1 throw on the crank is a weak spot and alot of guys break the cranks there. I'm debating about putting an outboard bearing support on the crank. I'm thinking it would help keep everything tied together better and maybe save me some expensive damage. I see the newer covers for outboard starting now have bearings in them. I'm going to self start so I would need to do a little machining on my own to make it work. Any thoughts?

Anyone care to share some crank damage pics from #1 letting loose.
 
Agemax said:
why oh why do people not state what engines they are refering to in threads?
Click to expand...

Well every one knows 1260 is a 5mm over 1100 right? :-k


The bike has a JE 1260 low compression kit in it, Gs1150 head with SS valves, and 370 lift megacycle cams. The bottom end has a GRC crank, Slider, and a R+D pro cut tranny. Bike runs on E85 and I built the motor.
Click to expand...
 
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have you got any ideas about how you are going to do this mod? sounds interesting, similar to a sprocket outrigger bearing i guess
 
I would use the stock cover and mount a cup style holder to the inside of the cover. I could use the mounts where the stator bolts to. Inside that I would mount the bearing. Then I would just slightly machine the end of the hub taking away maybe 2 or 3 of the threads to give the bearing a good place to ride just behind the bolt. I would leave enough of the threads so I could still get a puller on it to remove it from the crank.

I found a good bearing to use. 30mm ID 55 or so OD and rated at 15,000 rpm. The end of the hub is right at 30mm.

Looking at the cover I think the stator mount is strong enough for the job. The other option would be to machine the outside of the cover flat and mount a plate to it with the bearing holder attached to the plate. This second option would be a little more heavy duty.

Seems like they break right at the counterweight. Years ago I broke one there right at the shift. I still had the entire magnet assembly on at the time. After that I took the magnets off and lightened things up as much as I could. I'm just looking to take the next step. I don't know of anyone who has ever done this when self starting.

I see the new outboard starting plates have bearings in them. (From their website)APE developed this style of starter plate for the very high horsepower bikes that were experiencing left side crank throw failure.

This plate carries a bearing on the outside of the plate to give the crank support out on the very end. This prevents the crank snout oscillation that fatigues and eventually causes the destruction of the left side throw, causing catastrophic engine failure.
 
So is it the oscilation of the crank end that breaks them or does it have more to do with the torsional forces the crank sees on the shift changes. I'm talking about twisting forces on the crank at the shift when you go from 10,000 rpm to 9000 rpm in the blink of an eye. years ago I broke mine right at the shift. I did later find out that crank had the 1980 hollow left end on it. I have since switched to the small late model left ends that are much stronger.

The bike I'm building this for should go in the very low 9's to 8.90 range with a 10" tire. I expect this to be much harder on parts than my small tire.
 
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I had a #1 connecting rod, small end break just below the piston pin - once at 115 mph around the 1/8 part of the track. slippery situation.
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Machine the rivets in your alternator (what is left of it...) off and knock them out, that will allow it to come off the female taper. That will save more weight off the end of the crank, making it less likely to break. It is also easier to get the alternator off this piece than turning the magnets off as you did.

Do you have the big end or a late (no hole) small end? If you dont have a big end, get one.

I have been 7s at over 180 with this setup with the added stress of my external belt driven alternator and have never broken a left end, nor has anyone I have sold a kit to(that I know of) and that includes Big Phil (Tommy Miceli) and Brad Mummert.

With no alternator at all, you are extremely unlikely to break a left end.
 
I've run a outboard crankshaft bearing support for over 10 years.I average 125 passes per year. GS1150 based 10" tire bike with pushbutton start.I started with a piece of aluminum bar 3.5" dia. and1.5" long.Cut the id on a lathe to fit the stator mount in the stock cover. Mount to the threads in the cover and countersink heads.Open up the other side {towards engine} to72 mm go 0.687 "deep.I use a open bearing trade # 6207{McMaster Carr #5972k317}You will have to cut a small amount off the starter clutch to fit the id of the bearing but it is past the threaded portion used for the puller........Jeff
 
Do you have a pic? Would love to see it. Sounds like exactly what I was thinking of doing. Except I was thinking of putting the bearing outside of the threads instead of up past the threads. Have you had any issues with your setup? Also how big is your motor and how fast do you go?
 
Rosco15; I don't have any pics.Bike is out in the snow covered car trailer.I was scared to use threads for the inner bearing race,plus it might be harder to pull off the starter clutch.If you make the adapter too much thinner,it will be hard to hold the bearing and center the adapter. My engines are all 1425cc. Fastest this year 9.0 8.67 with different head. I'm a bracket racer.not a go fast guy....Jeff
 
I run a Gardner crank and use a PMFR outboard bearing support as extra insurance. The support is spendy at $265, but a lot cheaper than a crank and cases
 
Madjack; Do you have a PMFR part # ? The only one I could find there was for a remote starter.
 
I'm guessing the remote start is the one he's talking about. I don't see anything for self starting.
 
No one I know of makes a 3" offset motor plate to use with a stock starter. Greig Frankheim I think is the name of a guy in Australia that makes a cutout plate to clear all the starter clutch stuff but I don't think he puts a bearing support back in it. I could be wrong. Do a search for him on Dragbike.com. Ray.
 
I just shot Greg at MPE an email thru their contact page. See what I get back.
 
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