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#447080 - 08/01/12 2:45 pm C15 MX Big End bearing seizure  
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Alex Offline
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Seattle
OK, I need some help with this. I need to get to the bottom of this so I can race again.

Background: This is the C15 motocrosser I have built and have been racing over the last year or so in AHRMA MX competition. The bike is quite competitive and has been relatively reliable up until this point. The only motor issues have been last year in october at the Barber Vintage Festival I lost my air cleaner and ingested a lot of dirt and dust. The ring grooves were filled with dirt and the cylinder walls were heavily scored. The barrel was bored and fitted with a +.040" oversize and 0.0035" bore clearance (the recommended maximum). When I originally built the crankshaft, I installed a brand new alpha big-end bearing and the C&D autos timing side bearing conversion since it is a distributor motor. Unfortunately, when I went to build up the crankshaft, the big end bearing I had was an Alpha B24 type but the rod was for the earlier B23 type. This meant that, while I could use the crankpin and roller set, the outer race OD was too small to fit the rod. So, I decided to use the old outer race and hone it to fit with a clearance of <0.001". All this has worked fine for about five race events...until this past weekend.


The McKee's Farm AHRMA VMX event was in beautiful West Virginia set against a backdrop of gentle mountains on private farmland. The course was a grass track laid out by Dick Mann himself. It was wide open with few jumps and a perfect surface. Just the ticket for a roadracer on an MX track. There was only one other person in my class a Benelli 175 which just didn't have the oomph to catch the ceefer. So, I was mainly racing for fun and the possibility of spanking some of the later japanese 125's that were also running in our race. I got a great start and ended up third into turn one. Then it was on. I let the BSA sing and, while I couldn't catch the two Japanese bikes in front of me, I opened up a pretty good gap to everyone else. By the time I came across start/finish on the first lap, I was pretty much by myself. Then, disaster struck decelerating into a broad downhill sweeper. The motor locked up solid with no warning. No untoward noises...nothing...just silence. I was sure I'd stuck the piston. I pulled the plug, but it looked perfect.

The post-mortem revealed that the top end was in pristine condition. No top end seizure. But, oh horror, the big end was stuck. And when I say stuck, I mean STUCK. I've now stripped it down to the crank and the only indication of the seizure (aside from the bearing not rotating) is that the big end of the rod is definitely showing signs of overheating:


Next, I'll press it apart to see what what the big end looks like but I have to wonder what caused this:

  • Lack of oil? The pump is working great, but I wonder if enough oil is getting to the bearing. I ran the pump with just a screwdriver through the distributor hole and it is pushing oil out the bearing. Maybe not enough oil at RPM? Maybe the TS needle bearing is leaking too much oil?
  • Something I did honing the rod? What would the problems/symptoms be? What should I look for?
  • Is the current setup just not suited for sustained high rpm? Does it need a needle or plain bearing big end? End fed crank?

Any thoughts, feedback would be appreciated. I do NOT want this to happen again.

Cheers.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
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#447083 - 08/01/12 3:02 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Dec 2004
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kommando Online content
kommando  Online Content


Joined: Dec 2004
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Scotland
When you assembled the big end did you need to use any force to get the rod over the bearing, 0.001 sounds ok but unless the rod will go over the bearing using its own weight then its too tight a clearance and the rollers skid, other possibility could be the honing did not get a fully circular hole and there was a tight spot.

#447088 - 08/01/12 3:26 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Alex Offline
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Seattle
kommando, that is a distinct possibility. No, the rod did not slide on on its own, but neither would the supplied outer race that came with the bearing...and it had yet to be pressed into a rod. Maybe for high-rpm applications such as this more clearance is required?


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447091 - 08/01/12 3:44 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Dec 2004
Posts: 8,896
kommando Online content
kommando  Online Content


Joined: Dec 2004
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Scotland
The B24 I have still to be fitted to a rod will slide out under its own weight and I have seen advice that this is the clearance needed after the rod is fitted. I have 2 B50 big end and rod assemblies and one bought assembled slides under its own weight but the other one I assembled from different parts does not but will do before I fit smile , it has to be fully oiled assembly before testing.

#447092 - 08/01/12 3:50 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Dec 2004
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kommando Online content
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Scotland
And what revs were you doing, roller bearing big ends are limited to 7K, needle rollers will go higher but 8K plus needs plain bearing. There is a poster on B50.org who pulls more than 8K on a B50 but it has a B25 crank stroked and fitted with an A65 sized plain big end, once he dumped the Whitemetal shells he has clocked 130mph.

#447096 - 08/01/12 4:19 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Alex Offline
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Seattle
I don't know what revs I was turning (no tach) but I'm guessing it was probably north of 8K at times. I hate to have to completely re-engineer this thing. Maybe a tach is needed?


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447098 - 08/01/12 4:36 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Dec 2004
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kommando Online content
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Scotland
Long term I would look to get hold of the late WD B40GB needle roller big end, it fits the pressed up crank but the bearing is the same as fitted to a B50. Short term fit a new B23 or 24 with the right clearance and some fully synthetic oil.

#447099 - 08/01/12 4:38 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Arlo Offline
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Damn that sucks Alex. Maybe we'll get paired up again at Barber after you get it back in the grass!


-71 T120R well lubricated.
-66 T120TT
- A few Penton dirtbikes.
#447113 - 08/01/12 6:28 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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gunner Online content
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Farnham, Surrey, UK
Bad luck Alex, I have some random thoughts which may help centre in on the cause:-

- you mentioned the engine had ingested alot of dirt from the first failure and the cylinder was badly seized. Just wondering if any debris was left lurking somewhere in the engine, oil return lines or oil tank? Possibly some debris has managed to find its way to the big end?
- Are you using any kind of oil filter? Hopefully yes, which should negate the above issue.
- What kind of oil are you using? There is a theory that roller bearings prefer monograde, not sure how true this is or whether youre using it but maybe in future you should go for synthetic which seems the choice for competition bikes.
- I have never seen the C&D autos TS needle conversion, but as you say, maybe its loosing pressure and not supplying sufficient oil to the big end? Having said that, roller big ends only need a dribble of oil.
- Since the rod is blued and seized solid, the big end bearing is clearly heating up. This to me suggests either lack of clearance or lubrication or maybe both. Usually roller big ends fail through wear, start knocking and finally disintergrate. So a blued rod and seizure seem to support the lack of clearance/lubrication theory.
- what is the clearance between the rod and flywheel cheeks? Maybe the rod is binding on the flywheel?
- I guess revving the engine over 8k aint gonna help a roller bearing big end, still if the clearances and lube are sufficient then it might be OK

IM by no means an expert but I hope the above is of some use.

Last edited by gunner; 08/01/12 6:32 pm.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
#447119 - 08/01/12 7:34 pm Re: C15 MX Big End bearing seizure [Re: gunner]  
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Alex Offline
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Seattle
I really appreciate the input guys. I was really careful when I put this together and the honing machine does a really good job of making a round hole, though I didn't check that. The rod spun very freely on the bearing, though so I have a hard time believing there was any interference. And yes, I didn't mention there is a return line filter. I must say the oil is quite clean. I even flushed the oil tank again after the air filter incident. Axial clearance of the big end bearing was about .020"...I couldn't find a spec for it but that should be plenty.

Kommando's assessment makes the most sense to me right now. And as I go through engineering data for needle and roller bearings, it is starting to sink in that likely this is all due to the RPM/Load capacity being exceeded. All indications are that over 8000 is not suitable for a roller big end. I lightened the valve gear enough to where this thing will rev to the moon without considering the consequences.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447148 - 08/01/12 11:55 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Mr Mike Offline
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Alex, when you double the rpms from where it is normally supposed to run "s--t" happens. You have learned that before with your A 65 road racer. This old tiddler loves your stories but won't give you any sympathy.

Mr Mike

#447172 - 08/02/12 2:47 am Re: C15 MX Big End bearing seizure [Re: Alex]  
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John Healy Online content
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Boston, Massachusetts
A couple of things...

Max Nightingale of Alpha Bearings will be doing several seminars at Barber. I recommend any one who services flywheel assemblies, especially ones setup for racing, attend one of them!

I have seen several ways of of checking the bearing clearance but "did it slide on on its own" isn't one of them. I think we would be looking for .001 in. to .0011 in. for this application.

Also it is very easy to get the rod surface convex or concave. If the surface is convex it feels like the clearance is right, the rod rocks, but it can be too tight in the middle. This is a job where proper measuring equipment makes a big difference. A bore gage tells you a lot. Not only will it tell you if the hole is round but it will show you if the hole is concave or convex.

We do Vincents and with a perfectly prepared rod race clearance of .001 in. will give you .018 in. rod rock measured just under the wrist pin bushing. I use this a confidence check after checking the clearance with a bore gage.

One of the problems we see with Vincents, and I can see that when one of these rods is used in anger, is the big end eye going out of round. Instead of the race being pre-finished so you get the big end assembly from Alpha with the race in place, the bore of the replacement rod race is some .005 in., or more, undersize. This allows you to hone the race round after installing.

When first started learning how to do lower ends some 50 years ago we had to lap the rod race. The first check was to lap the rod until when the rod is spun on the crank pin it doesn't try to screw up the pin. When it stopped screwing up you were within a couple tenths of being on size.


#447196 - 08/02/12 7:40 am Re: C15 MX Big End bearing seizure [Re: Alex]  
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wak Offline
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derby england
I would try and get a genuine big end not alpha,the timing side roller in ways is a good idea but its not so good at getting oil to the big end the clearance as to be as tight as posible other wise it escapes past the rollers,end feeding the crank would be the best option and as you aready have the roller timing side it could be done using basic tools,you need to block the existing feed to the timing bearing and tap into it then feed it down a quill down the end of the crank.doing this you also gets the bonus of cenrafugal oil feed to B/E.Dont worry about revs it will run out of power before B/E failier.


BSA CYCLONE
BSA METISSE
TRIUMPH TR6C
BSA BUSHMAN
INDIAN WOODSMAN
#447226 - 08/02/12 12:47 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Dec 2004
Posts: 8,896
kommando Online content
kommando  Online Content


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Scotland
Quote:
The first check was to lap the rod until when the rod is spun on the crank pin it doesn't try to screw up the pin. When it stopped screwing up you were within a couple tenths of being on size.


Which matches the comments I made as just prior to the weight of the con rod being enough to slide over the bearing you have to screw the con rod over the bearing to get it to move it over the bearing.

#447227 - 08/02/12 1:08 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Alex Offline
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John, I will DEFINITELY put that seminar on my calendar. I honed the rod on my sunnen honing machine and measured it with a bore gauge. I did check for ovality but not really roundness since the CMM at work was down. It checked out...but I cant say that I checked sizing anywhere but at the center. Again, kind of depending on the hone to do a good job there. Last night also got me to thinking: while I know most standard bearing races are full hard, maybe the stock ones were case hardened? I did have to hone about .006" depth off them...


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447236 - 08/02/12 1:44 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Mar 2005
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John Healy Online content
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Boston, Massachusetts
While I cannot speak to the BSA rod, a Vincent rod will slip on to the pin as the clearance approaches 6 or 7 tenths (.0001 in.) but will still show tendencies to screw when rotated. It isn't till it get close to 9 tenths that it stops screwing. But for a Rapide it is at .0009 in. that you must stop honing. But to use "dropping" leaves people reading this that I just have to hone out the rod until the rod drops on the pin. This isn't the case.

What I reeled from was the thought of honing the eye of the big end until the rod falls of its own weight. At best this would take a lot of skill, as you are trying to feel the difference of a couple of tenths from how the rod dropped onto the pin. At least the feel of the rod trying to screw gives you a subtle clue as to what is going on.

But today, with the easy access to basic measuring equipment that wasn't available when I first learned all this, there is no need for learning any of these artisan skills. Measure it and be done with it.

While with a Power Stroke machine you can eliminate a lot of the common problems when hand honing with one of these machines, you still have to dress the stones properly. When hand honing you cannot assume that the rod race surface isn't convex or concave especially at the top and bottom. It is easy to lever the rod as you move it back and forth which creates an odd hole being small in the middle and bell mouthed mostly at the top and bottom.

I doubt seriously if the original race was case hardened.

Take that sucker apart and let's see what happened...


#447239 - 08/02/12 1:51 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Alex Offline
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Yea...I need to get it apart. One of these days I'll have my own press, until then it's "hit up a friend".


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447244 - 08/02/12 3:10 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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wak Offline
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wak  Offline
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derby england
in the dark ages i used two steel wedges to part them and a big vice to put em together,i still feel its an oil problem,if honing the bearing out had hurt it it would have developed play.in my time doing them in shops i worked in and my own stuff , all the seized ones had got no or too little oil.


BSA CYCLONE
BSA METISSE
TRIUMPH TR6C
BSA BUSHMAN
INDIAN WOODSMAN
#447246 - 08/02/12 3:36 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Alex Offline
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Seattle
Here's a video of the start to entertain you until I get it apart:


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447247 - 08/02/12 3:45 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Mar 2005
Posts: 9,971
John Healy Online content
John Healy  Online Content


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scroll to the bottom:

http://www.thevincentparts.com

Did these with my stone axe...

I just don't play one on TV...


#447250 - 08/02/12 4:05 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Alex Offline
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Alex  Offline

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Seattle
Wow...nice stuff.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447919 - 08/06/12 5:12 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Alex Offline
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Alex  Offline

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Seattle
OK, thanks fer your patience folks...here is is:


Looks like the cage started to disintegrate at some point and the rollers just rolled the aluminum bits under. This I guess caused more bits to get rolled under until it eventually just stuck. I've had no luck finding a needle bearing so I think I'll just go with the standard bearing again...but install a tach and try to keep the revs down.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#447930 - 08/06/12 5:54 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
Joined: Sep 2004
Posts: 680
gunner Online content
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gunner  Online Content
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Farnham, Surrey, UK
Dunno if this is any help, but there is a nos C15 rod complete with big end bearing on eBay USA, look Here

Last edited by gunner; 08/06/12 5:55 pm.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
#447935 - 08/06/12 6:12 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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Peter Quick Online content
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The eBay rod gunner mentions has no roller bearings. Just a smooth bushing. These rods went through a number of upgrades, from plain bushing, to set of 10 1/4" x 12" rollers, to 24 1/4" x 1/4" rollers with a larger diameter rod big end eye, to yet another larger diameter rod big end eye with same number of rollers, etc.. Not all the cranks and rod combinations work together. I'd want to put in the latest beefiest rod and big end bearing if riding hard.

Peter


check out: www.bsaunitsingles.com
2500 BSA part numbers with inventory in stock just for the unit singles!
#447938 - 08/06/12 6:39 pm Re: C15 MX Big End bearing seizure [Re: Alex]  
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gunner Online content
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gunner  Online Content
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Farnham, Surrey, UK
Quote:
The ebay rod gunner mentions has no roller bearings. Just a smooth bushing.


Actually if you look carefully at the second image, you can see rollers through a semi transparant plastic cover.

According to the Rupert Ratio manual page 57, although the early C15 big ends were plain with a larger shouldered big end pin, there was subsequently a replacement caged roller big end with a straight big end pin to accommodate the rollers. Maybe this rod and bearing is the later roller replacement version of the earlier plain type?

Agree about using the strongest possible big end available


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
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