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#585678 - 02/15/15 9:39 am Crankshaft big end rebuild  
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MrBSA Offline
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Orlando, Florida
I am restoring a B34 engine. The big end had some play in it, so I split the crank and removed the pin. I have new pin and bearings with cage along with new race. Does anyone have information about pressing the crank back together and aligning flywheels. I have done research, but the information I can find is minimal. I am looking for practical tips on how to make a jig, and align the flywheels. Not just hit them with a lead hammer, which is about all the work sheet says.

Thanks, Harris

BSA Gold Star eBay items

BSA Gold Star forum This board is dedicated to BSA Gold Star motorcycles.

#585681 - 02/15/15 10:23 am Re: Crankshaft big end rebuild [Re: MrBSA]  
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Tribsauk Offline
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Death row next in line norfolk
Hi Harris This is a link to WDM20 site which contains some useful info on crankshafts although M20 but the same set up as B33/34.

http://www.wdbsa.nl/crankshaft%20rebuild.htm

http://www.wdbsa.nl/crankshaft%20tool.htm

This is a practical thread written by Dave plumb he also has other threads on cranks on same site I hope it is of help.
I have made my own jig to realign flywheels if interested I,ll post some photos, easy to make and has saved me a time and money trying to get someone who understands what they are doing.. Dave


1941 BSA WM20
1958 TRI-BSA 750 PRE UNIT
1957 THUNDERBIRD
1932 R E MODEL GS SPECIAL
1947 BSA YM21
#585690 - 02/15/15 11:17 am Re: Crankshaft big end rebuild [Re: MrBSA]  
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Cork Ireland
Hi Harris
Good advice on the M20 link, but not really a job for someone who has not seen it done before
Do not hit the flywheels when the crank is supported between centres !!!!!
I do not use a hammer preferring to bump the flywheels in the required direction on end grain of an oak block

HTH
John

#585718 - 02/15/15 1:47 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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MrBSA Offline
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Dave, thanks for the links, that is what I am looking for. Also if you do not mind, I would greatly appreciate a couple of photos of your jig. John, I have not seen it done, but I understand the concept, also I am already well beyond do not do it. Good advice about not hitting the flywheels when supported. Thanks

Harris

#585731 - 02/15/15 2:50 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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kommando Online content
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#585749 - 02/15/15 3:54 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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Death row next in line norfolk
Harris will take photos and post. My jig uses small roller skate type bearings, the mainshafts sit on these and I have a dial guage fitted for runout and to true up the shafts, I dont trust using mainshaft centres as these always had a knock or two from P.O much better to take measurements from shafts as these are where the bearings run . You will note that Dave Plumb uses HD oversize rollers in his big end rebuilds I have used them and they work well I used a new pin, HD rollers and had the original outer conrod bearing track honed to size, last one I done was for my old B33 well pleased with result.. Dave


1941 BSA WM20
1958 TRI-BSA 750 PRE UNIT
1957 THUNDERBIRD
1932 R E MODEL GS SPECIAL
1947 BSA YM21
#585813 - 02/15/15 7:42 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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Rich B Online happy
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Stone Creek OH USA
Harris,

Unless you have your mind made up to do it yourself......most shops that do 2 stroke cranks will have the necessary tools to align the flywheels. May even find an HD shop willing to do the deed. You will just have to babysit them thru the tapered pin and tightening the locknuts.

My local BMW shop actually has the tools and does my BSA and Bultaco cranks....


Life is too short to drink cheap, bad beer.
#585959 - 02/16/15 3:27 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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Mr BSA ... Years ago I was a bit handy at rebuilding Goldie cranks. Some ideas for you, nothing new, but a bit of 'yackity yak' on the subject:

As has been suggested this may well be a good time to find a shop to do the job. A common issue with Goldie cranks is the pin tapers have moved in the 'junk' steel wheels. This is obvious noting the 'fret' marks on the pin tapers. I once went to the trouble of lapping in a new pin in fretted wheels. Sucked. I've heard stories of knurling the pin tapers by the pro tuners. Dennis M.??

One of the handiest jigs is a bit unusual I believe, but the concept is/was used aligning multi cylinder built up cranks. It's made from a short length of steel tubing, split, with drilled/tapped tabs welded on either side of the split. The 'ring' is welded to a heavy steel channel base.

You fit the crank assembly in the fixture and tighten the bolts, clamping the flywheels straight. (You did align the oil hole in the pin/wheel?) Now you can tighten the crank pin nuts, snug but not finish tight using a 1 9/16" socket with the face turned flat in a lathe to insure a usable fit on those thin nuts. A impact wrench is strongly suggested.

Now put the crank in the aligning jig. The 'book' suggests using vee blocks on the bearing areas of the axles. I use a fixture made up with a heavy steel base with a pair of heavy steel upright bars bolted on with a pair of ball bearings on each upright the crank sits between. Then using a dial indicator on the bearing journals, I've found the crank alignment very close after previously using the clamping fixture. After alignment with the lead hammer re install the unit in the clamping fixture and finish tightening the pin nuts and don't forget the nut locking screws
BTW, this fixture also works nicely for balancing cranks.

Bear in mind a well tuned Goldie engine will rev high enough to hurt itself. Looking for 'an edge' many of us would rev over 8k which is close to the limit. Having destroyed one GS engine with a broken rod, the most typical failure, I also once broke a crank pin at moderate revs on my road GS.

However ... For some time I and many others world wide are using Phil Pearson's beautiful pressed up cranks with cro-mo wheels, GM speedway pins and Carillo rods as do many other GSrs world wide. The only failures I'm aware of is the rod big end needle bearing going bad. I do question the use of needle bearings vs larger rollers. hmmm?


dave - NV
#585964 - 02/16/15 4:03 pm Re: Crankshaft big end rebuild [Re: dave - NV]  
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Tribsauk Offline
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Death row next in line norfolk
This is the jig I made up from some odd steel I had laying around and four small roller bearings.. does the job also I use it for balancing cranks as I have overbored my BSA WM20 & used a different piston.My MK2 version of this jig will have adjustable legs for cranks with different size mainshafts although I have used this with a good success rate and have checked a crankshaft I have trued on my mates Alpha jig which he wont lend me without me using at his place which is a pain as I like to take my time and use my own tools,hence I made my own jig.Anyway if you feel confident it not rocket science but as said check for taper wear and loose rivets on mainshafts.. Dave









1941 BSA WM20
1958 TRI-BSA 750 PRE UNIT
1957 THUNDERBIRD
1932 R E MODEL GS SPECIAL
1947 BSA YM21
#585980 - 02/16/15 5:49 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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MrBSA Offline
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Orlando, Florida
Thanks for all the info, this is the kind of information I was looking for. Including Rich B's suggestion to farm it out. Still might do that. Although the info on the jigs from Dave-NV and Dave's pics are kinda what I had in mind. I am surprised that there was no info on this subject in the archives. Kinda makes me nervous, that I am first person to ask. Does this mean that everyone else is too smart to want to do this themselves?

Thanks, Harris

#585983 - 02/16/15 6:01 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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Magnetoman Online content
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Originally Posted By Rich B
most shops that do 2 stroke cranks will have the necessary tools to align the flywheels. May even find an HD shop willing to do the deed. You will just have to babysit them thru the tapered pin and tightening the locknuts.
Originally Posted By dave - NV
As has been suggested this may well be a good time to find a shop to do the job.

Bear in mind a well tuned Goldie engine will rev high enough to hurt itself.

For some time I and many others world wide are using Phil Pearson's beautiful pressed up cranks with cro-mo wheels, …
A question for Dave. If you could not use a Pearson crank, and given that you know the stock one isn't bulletproof, would you trust some guy at a general purpose engine repair shop, or at a Harley shop, to properly assemble your Gold Star crank so that it could survive hitting 8000 rpm (either on purpose or accidentally)? I suspect not.

Unless someone does this job himself, or has the jig and other tools to confirm the Harley shop actually did align and assemble everything properly, it seems to me that exceeding the ~4000 rpm where a Harley engine has its maximum torque would be placing unearned trust in some mechanic who there's no reason to believe works to the necessary standard.

#586004 - 02/16/15 7:59 pm Re: Crankshaft big end rebuild [Re: Magnetoman]  
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There actually are people who work at HD shops (and other brands) who are also enthusiastic about motorcycles. So slagging them off as not working to the necessary standard is bullsh*t. Maybe I have been lucky, but I have been invited to stand beside the mechanic in the shop and walk them through the nuances of doing a BSA crank.

And the mechanic was more than willing to learn and follow instructions. Enthusiastic comes to mind. And a "thank you for letting me set up the crank, I enjoyed it". Of course that crank wasn't all that straight, think we had .0005" total run out. Smoothest turning bottom end I had built to that time......yea I thanked him too.

I wouldn't take a crank to a shop, drop it on the counter, and ask when it will be done. I would talk to people and see who they recommend. Then go to the shop and talk to the service department. If they sound truly interested and will work with a bit of supervision, you can get the "standard" you are so worried about.


Life is too short to drink cheap, bad beer.
#586008 - 02/16/15 8:35 pm Re: Crankshaft big end rebuild [Re: Rich B]  
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Magnetoman Online content
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Originally Posted By Rich B
There actually are people who work at HD shops (and other brands) who are also enthusiastic about motorcycles.
Yes, but enthusiasm and skill are two different things. There are plenty of people who are highly enthusiastic about motorcycles who don't have the skill to assemble a Gold Star crank.
Originally Posted By Rich B
So slagging them off as not working to the necessary standard is bullsh*t.
If you re-read what I wrote you will see that I didn't slag them all off. However, your experience isn't typical since most places won't let the customer stand beside the mechanic doing the work. So most times someone would have to place their trust that some guy will work to 0.0005" standards. If someone does a perfectly fine job assembling cranks that won't get reved past 4000 rpm it would be placing undue trust in them that they would do the better alignment job necessary for 8000 rpm (forces go as the square of the rpm so they are 4x higher at 8k).

#586099 - 02/17/15 2:18 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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Death row next in line norfolk
think we had .0005" total run out..

I normally go for 2 thou run out and thats on M20 & B33 cranks.
As for shops doing the work I once gave a engineering shop a crank to assemble and true which I had stripped / cleaned and prepared ready for rebuild what I got back was a poorly assembled crank which when put into the crankcases didnt align and made the cases wobble when turned.So I decided to true it myself this is when I found the crank pin nuts were not tightened correctly .. hence my need for a jig..Dave


1941 BSA WM20
1958 TRI-BSA 750 PRE UNIT
1957 THUNDERBIRD
1932 R E MODEL GS SPECIAL
1947 BSA YM21
#586101 - 02/17/15 2:32 pm Re: Crankshaft big end rebuild [Re: Tribsauk]  
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Originally Posted By Tribsauk
My MK2 version of this jig will have adjustable legs for cranks with different size mainshafts
An alternative to consider is making a sleeve to bring the OD of the smaller mainshaft up to that of the larger one. Even with a 0.001" slip fit for the sleeve the heights on opposite sides of the jig almost certainly are going to be closer than you could achieve with adjustable legs. And, even if the heights are off by a few thou. that won't affect the accuracy to which you can true or balance the crank.

#586111 - 02/17/15 4:21 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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Tribsauk Offline
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Death row next in line norfolk
Hi MM my jig as it is now doesnt affect accuracy between different size mainshafts as I said earlier I checked out a crank I had trued on this jig with my mates Alpha made jig and it was spot on. I do intend to make a bigger version of this one for wheel trueing however.


1941 BSA WM20
1958 TRI-BSA 750 PRE UNIT
1957 THUNDERBIRD
1932 R E MODEL GS SPECIAL
1947 BSA YM21
#586121 - 02/17/15 6:17 pm Re: Crankshaft big end rebuild [Re: MrBSA]  
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flowboy Offline
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I face having to do this soon on a project. I've been lucky to have a local time served engineer with a love of big singles do this for various BSA's of mine including a couple of racers with original cranks (sharp intake of breath!) One broke a rod in it after I'd sold it after 2 seasons, the other survived over 8 seasons!(big end failure) Trouble is, said engineer has now retired & moved away. We definately miss his skills here.
One thing I do know is an apparently ok crank can have loose shafts. They're hard to spot - after parting the wheels, lay them on the bench & take a very firm grip of the shaft & try to "bend" it; look closly at where the shaft comes through the wheel - you may well spot a little gleam of oil as you "flex" the shaft. The wheel will be past it's service life... i.e you'll never get it to .0002 let alone .0001 or even better run out. This can happen even if the "top hat" flange has been welded to the wheel on the inside. It's very likely to happen on high rev. & often over-revved race engines but all these BSA singles are ancient now so they will all have received hideous abuse over the years! There are a few good ones about tho' - my 2nd racer was only a turned down b33 crank.
Pearson's cranks are lovely; but are larger dia. than std so they tend to bind with the holding down bolts on crankcase assembly. N.E.B. cranks are also pretty good from what I hear. Similar prices.

Last edited by flowboy; 02/17/15 6:21 pm. Reason: a little detail

na

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