Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board tappet trouble

My exhaust tappet "ledge" or "shelf" height from spindle is greater than the lobe diameter at the lowest point of NOS 2446 cams.
That minimum bore to lobe dimension is 3.00mm.
The shelf is 3.02mm from spindle to shelf.
The tappet would be prevented from running on the lobe, instead on the shelf until lifted.
Dremel time?
Finding this hard to believe this could have been made like this.
Harder if it was run,
Harder if in fact there are others out there,....

Which engine are we talking about ?

2446 suggests pre unit single be better to be more precise.

Your post makes no sense at all, "shelf" and "ledge" are not terms normally associated with cams and tappets

Heff's past posts on other forums have been in regards to a 500cc Gold Star.

Lannis

2446 usually means Clubman Gold Star exhaust cam. Here's an image of the timing side case. Might help. Don't see any shelf unless maybe it's the flat machined on the cam spindle that's there for tappet clearance.

Heff, can you post a photo of the problem area?

¿ I think he may mean ...
the exhaust-cam-follower ... cant drop all the way down ...
to the cam-base-diameter ... because it gets hung-up on those "milled eyebrow" ( ledges )
on the upper-side of the cam-spindle hole ( and "flat" on the spinde )
... so spindle is possibly installed incorrectly

... image : courtesy of MM
https://www.britbike.com/forums/ubb...tar-engine-rebuild-bottom-end#Post810584
dont know much about goldstars ... but doesn't ... the pressed in part of spindle , have a "flat" , that's supposed to be installed up
.. to help prevent distortion on the weaker , top side of case hole ?

It's entirely possible the spindle is in wrong so the flat on the flanged part is not facing up. That could keep the tappet from dropping all the way down to the base circle.

And that other flat you mention, the one on the pressed in stub, it actually is aimed toward the main bearing housing, not upwards, so there are two parts, one for intake and another for exhaust.

Thanks to all!
Honestly, had trouble posting this and then away.
Did not realize post was successful!

I put my description of the shelf/ledge in quotes to describe the machined flat in the timing side case. Assuming all more knowledgeable would get what I was referring to.
Milled eyebrows,...

Yes - this is a 500 single. CB cases.

The spindles are installed with their flats oriented horizontally, parallel with the flat, (eyebrow, ledge, shelf).
Note - the flats on the spindle flanges are below the milled surface. I have not measured this but would say the milled cut is about 1mm above the flat.

Measuring without cams using feeler guages- from spindle to tappet face (face resting on eyebrow)
Intake - 2.75mm
Exhaust - 3.02mm

The 2446 cams I have both measure 3.00mm - bore to low point.

This means:
The intake would be lifted 0.25mm clear of contact.
The exhaust will land on the eyebrow, not in contact with cam.

If the milled, or cast in eyebrow is supposed to be "flush" with the flat of the spindle flange then we have a problem,.....

Clue as to how to add photos?

No problem. This is an active forum here. I've posted in other forums (JetSki) and never got any response at all, even months later.

Yes, the tappet needs to contact the base circle to properly adjust valve clearances. Your first comment about going at it with a dremel might be in order. You will need to carefully protect anything that you don't want filings getting into.

But thinking about it just a little, you might be able to carve away just enough of that soft aluminum using a small wood chisel with a dab of grease on the edge to hold the chips. .02mm is about .0008" ie 8 tenths of a thousandth so you don't need to remove much and that way the swarf would be easier to deal with.

A less careful man would have just installed things as is and the tappet would have eventually worn that high spot away. Would the BSA works have done such a thing? Who knows.

Woodwork is my profession.
Don't usually think of appying those tools on motors,....
But - worked fine.
Much better than flying chips.
And more control.
Tappet now contact base cam diameter.
I may shave a tad more.
Would like to have .015-.020 clearance.

Not sure why this is like this.
If others have encountered
Wonder how many will think I am a butcher

Don't really care - if the solution works and we can move forward.

Tuners may reduce the base circle of the cam to gain more lift

even a regrind of a worn cam , to restore original lift ,
would require a reduction of the base Circle .

Regrinding Base Circle to restore lift of a worn cam. I think I actually understand that concept.

Glad it worked out. Since the base circle really doesn't wear, .005" should be just fine. Contact with the base circle mostly comes into play when tappets are being adjusted. (Or if your valves have gotten too tight, but you don't want that.)


It could be a simple stack up of tolerances, a little here a little there that ends up with interference.

Another possibility is a worn tappet. Round tappets that are free to rotate sometimes wear concave ie more in the center and less toward the periphery. That could be part of your issue. Unfortunately the entire top end needs to be removed to unscrew the tappet guide so the tappet can be removed to check it and have it re-surfaced if needed. And actually, it is a good idea to fit a new tappet with a new cam.

Maybe I'll send this one out for a regrind . . .

Let me look DEEEEP into my crystal ball. I see..... I see.... jyess I can see it now..... four welded lobes in your future. (But I can't help but suspect you're joking.)

Hope that was an April 1st joke.

You can get half decent A65 cams second hand for not much money, but new ones are not all that expensive either. However if you’re fitting a new or replacement cam, it’d be worth your time having the cam followers re-ground too. A lot of them for sale are pretty worn. Standard radius being 1.25” for an A65/A50. Unless you get an aftermarket cam then the radius may differ.