obscure big end assembly for C15

[shoal48]

Morning all, Ive acquired a C15, completely stripped over 30yrs ago and Im starting to restore it. One of the "bits" is a "new" roller big end assembly fitted in a standard early 40-48 conrod. its still wrapped, in perfect condition and over 30yrs old.

At first I assumed it was the standard Alpha replacement for the C15 which I believe uses 24 1/4" caged rollers, 2 across in 12 pockets. On taking it apart though this one uses 3/16" caged rollers, 3 across in 10 pockets.

There are no markings on the assembly and I have not been able to find any info about its origin. I did try an AI search which said it was made by PES of Loughborough and referenced a 40-0048KIT they make for early c15's but having contacted them they have never made anything like it and were never based in Loughborough and they kit referenced is not the same, so the AI was completely wrong.

The assembly seems well made and nicely finished so hopefully I can get it installed but it would be nice to know what it is and whether there are any likely issues before I do.

[rhyatt]

Draganfly have a roller big end assembly about £140.
But intended for a scrambler C15 rod.
I'm in the middle of sorting my own C15 and bought 1 of these to replace the plain bush big end currently fitted and worn out.
But the machine shop says the rod will need a slight bore out to accommodate this new big end bearing.
Is yours this draganfly.co.uk unit ??

[Rupert]

Sounds like it's the alpha roller bearing for the 40-48 rod. The type you describe with 24 1/4 x 1/4 rollers is for the later 41-234 or 41-181 rod and is a bigger bearing altogether.
You will probably find that the crankpin in your big end bearing is plain and not shouldered and should be 15/16" diameter if for 40-48 rod.
If the crankpin is plain and 1" diameter it is the slightly larger version for a B40 41-55 rod and won't fit your rod. bearing is too big

[shoal48]

Sounds like it's the alpha roller bearing for the 40-48 rod. The type you describe with 24 1/4 x 1/4 rollers is for the later 41-234 or 41-181 rod and is a bigger bearing altogether.
You will probably find that the crankpin in your big end bearing is plain and not shouldered and should be 15/16" diameter if for 40-48 rod.
If the crankpin is plain and 1" diameter it is the slightly larger version for a B40 41-55 rod and won't fit your rod. bearing is too big

thats interesting. I had an early alpha big end fitted to my first c15 back in 1969 but must admit I didnt have opportunity to take it apart and examine the roller setup, so, did the early alpha use 10 pockets of 3/16" x 3 rollers for the 40-48 conrod? The bearing was already fitted into the rod when i got it. The crankpin is plain, not shouldered and is 0,947" so bigger than 15/16" and smaller than 1" Can I assume that this crankpin will fit into my exisiting flywheels which presumably are 60/61 with a 40-48 rod.

[shoal48]

Draganfly have a roller big end assembly about £140.
But intended for a scrambler C15 rod.
I'm in the middle of sorting my own C15 and bought 1 of these to replace the plain bush big end currently fitted and worn out.
But the machine shop says the rod will need a slight bore out to accommodate this new big end bearing.
Is yours this draganfly.co.uk unit ??

the draganfly unit looks the same externally and seems to use a plain crankpin rather than a shouldered one, but there is no reference to what bearings it uses and alongside the pic for the c15S bearing it shows loose 1/4" x  15/64" rollers whereas the unit I have uses 30 x 3/16" rollers in 10 rows of 3

[rhyatt]

I must admit I haven't seen the innards of this roller unit.
The machine shop has the crank and is rebuilding it for me

[Rupert]

I've seen this design of big end fitted with long one-piece rollers and multiples of shorter rollers. Probably depends on what is available at the time of manufacture.
Good that it is already fitted to your rod, that confirms it is correct for your C15 rod not b40! The crankpin size you quote is 10 thou over the nominal 15/16" size. Probably best to have your engineer measure both pin and hole accurately and give a judgment on whether the resulting amount of interference is correct.

[rhyatt]

He has assessed my rod ID and the OD of the new BE assembly and assures me that the small amount of metal to be removed will leave enough meat in the eye area

[Rupert]

I was referring to the correct interference fit of the crankpin in the flywheels

[shoal48]

I've seen this design of big end fitted with long one-piece rollers and multiples of shorter rollers. Probably depends on what is available at the time of manufacture.
Good that it is already fitted to your rod, that confirms it is correct for your C15 rod not b40! The crankpin size you quote is 10 thou over the nominal 15/16" size. Probably best to have your engineer measure both pin and hole accurately and give a judgment on whether the resulting amount of interference is correct.

I thought I had posted an update reply yesterday but couldnt find it so sorry if this repeats something already said   I got a decent calibrated micrometer yesterday and remeasured the crank pin on the new replacement big end assembly. Its 0.9420" and not the .947 I first I thought it was, based on a cheap digital calliper. as the default size is 15/16" (0.9375) this makes my crank pin 4.5 thou oversize.

I understand the interference range should be between 1 & 3 thou oversize and am just wondering whether 4.5 thou interference would put too much stress on the cast iron flywheels or would the crankpin need relieving by a couple of thou. I'm not assuming that the workshop will be aware of the correct interference range for this assembly so would value an experienced view as to whether this is a cause for concern or not

[Rupert]

Maybe measure the size of the old crankpin as a comparison? The fit of the crankpin into the flywheels should be tight, far tighter than a bearing interference fit for example. The other useful indicator is how much force was needed to push the old pin out of the flywheel.

[shoal48]

Maybe measure the size of the old crankpin as a comparison? The fit of the crankpin into the flywheels should be tight, far tighter than a bearing interference fit for example. The other useful indicator is how much force was needed to push the old pin out of the flywheel.

good thought, I'm taking the crank to MJ Mcycles of Coalville, they have been around for ever and I suspect they probably know everything there is to know about these cranks   

[rhyatt]

just to resurrect this thread please.
my engineering shop is pressing the flywheels together soon/now.

as this new draganfly roller crankpin is a plain pin , there is no shoulder up to which the flywheels can be pressed.
therefore the question is please --
how much to press the flywheels together without pinching the new big end/conrod - is there a tolerance suggested -
this squeeze will affect the end float on the assemble crankcase/crankshaft