Britbike forum Forums British motorcycles in general Bsa gold star forum BB34 Cams advice required

I have finally made a start on my early '53 BB, a previous owner rebuilt the engine for scrambles but did not run it. I need some advice on what cams might be suitable for open road touring. I have had a look at the cam charts and think a 2450 would be good for the exhaust but what should I use for the inlet?

The cams I have are:

65-2436

65-2450 use for exhaust?

65-2446

65-1891

I have a good bore with a 7.5 to 1 piston, new mains and big end and will be running a 1 5/32 TT carb.

I think these are mostly exhaust cams, but I did read somewhere that the profile of some exhausts and inlet cams were the same. I guess the difference is in the marking when you time the engine. I think I have the skills to time an exhaust cam as an inlet, but am short of knowledge on what cams might suit best.
Can anyone offer advice that will reduce the pain of buying a new cams ?

65-2448 (intake) 65-2450 (exhaust) are the "touring" cam set.

65-2446 is an exhaust cam, also used as an intake cam on later "scrambles" engines. I run the 2446 pair on my DB (DBD head, 1038 Concentric) and really like the combination, makes them a beast in the mid-range

I don't have my cam chart handy...but for some reason, I was thinking 65-2436 is a touring cam with no quieting ramps. 2438 was the rest of the pair.

The 2436 (exhaust) and 2438 (intake) were the original touring cams and the 2448 (intake) and 2450 (exhaust) were later the same profile except with ramps.


Bill B...

+1 on Boomer's comments.
I have run a BB34 on 2436 and 2438 touring cams. It was a really tractable and enthusiastic engine. BUT... The valve clearances are super small and difficult to set accurately. Also, valve clatter goes through changes until everything is equally warmed up, then the noise settles down. I found that annoying.

The later version 2448-2450 cams with ramps run much quieter and the larger clearance is much easier to set with a feeler gauge. I think you'd be plenty happy with them.

But then, I have a set of scrambles cams in a small port CB34 dual sport bike right now and they run great too. Good low end but still willing to rev. Tough choice. So then, I'd say just go with what's easiest to source.

I recommend 65-2446 intake and 65-2450 exhaust. I think that is the best set if you don´t like to buy new cams.

I can not recall, BSA ever used that combination on Gold Stars of any size..

Motolab is right. That wouldn't be a proven combination.

A quick Google search shows cams selling for between around $150.00 to $250.00. The used one on ebay looked pretty crusty.

This poster might still have some cams available.

https://www.britbike.com/forums/ubbthreads.php/topics/858560/bsa-gold-star-cams-fs#Post858560

I run the 2436/38 combo in my BB34. Nice power through the range but as Stuart says, a bitch to adjust the followers. I got tired of trying to use the feeler guage at .002 so I just got used to the feel of perceptible clearance and call it good. It's not easy with using two wrenches, a feeler gauge, and oversize arthritic fingers in a 2" x 3" opening to get an exact clearance. I would run the 2448/50 combo with .008 and .010 but it seems one of those i do have, can't remember which, and the other is scarce.


Bill B...

I seem to remember I needed three wrenches. And I made a forked feeler gauge so it would stay in place better and not fall out when the tappet turned a little.
PITA!!

Thanks for all the advice, it is very helpful.
I think I it is clear that the 65-2450 will work in the exhaust.
As I have a 65-2448 I think I will try that first in the inlet and if I am not happy with the results I can switch to a 65-2446.

I was thinking I could squeeze a bit more compression if I used a thinner head gasket, I would need one about 25 thou thick to take it up to an estimated 8.5 to 1. Could I use a DBD gasket and peel it down to that, is it the same hole spacing as the BB engine?

Probably more silly questions to follow!

Regards

Gordon

I would first install the 2448/2450 cams, then measure the distance between piston and valves and head with some plasticine and if the distance is sufficient, reduce the thickness of the head gasket.

We've dealt with this before. The Gold Star doesn't have a head gasket as such, instead relying on direct head-to-sleeve contact to seal the combustion chamber. The peel-apart "head gasket" is only used to seal the pushrod tunnel and has no effect on the piston-to-valve clearance.

If you raise the compression w/o changing the piston, the distance between piston and Head will be reduced. so the distance to the valves will be reduced, too.

Yes, the BB and the DBD use the same peel-able shim gasket with the same bolt spacing.

And yes, you could bump your compression with a thinner gasket BUT, you would need to machine down the liner spigot to accommodate that thinner gasket. This is not generally advised. For example, .010" thinner on your gasket would adjust your compression approximately .15 higher ie 8 to 1 would increase to 8.15 to 1. It's probably not worth the effort.

Also, you would want to know your starting point ie what the C/R is right now. First cc the volume of your combustion chamber with piston at TDC, then pull the head and measure your bore and stroke, then do the math to calculate your C/R. Once you know that, you're better informed as to what to do next.

Here in California, 91 octane is the highest that is widely available at the pump. My Goldie is 9.2 to 1 right now and is not very happy on pump gas. So you don't want to go too high on one of these for street use.

The only two ways to do that would be to machine the bottom of the muff, or machine the recess in the head that seals against the sleeve. The OP doesn't mention planning to do either of those things. He planned to raise the compression by reducing the thickness of the head gasket but, as I pointed out, it doesn't have a "head gasket" that does anything but seal the pushrod tunnel.

Or, as Stuart posted before I posted mine, a third way would be to slightly reduce the projection of the sleeve. He also pointed out how little in CR there would be to gain by doing that.

Hi, Thanks for all the advice, all very helpful. I should perhaps mention that I think that I am an experienced restorer, but, this is my first Gold Star in 47 years, there have been a few changes in that time. I will try and give more detail in my postings to clarify.

I understand how the Gold Star head seals to the barrel on the flange. Perhaps I had not fully explained, I had completed a trial fit of the head and barrel to check that the flange would seal. I then used feeler gages to check the remaining gap between the head and barrel to check the gasket was going to seal the pushrod tunnel etc. I am left with a gap of 25 thou. The current copper/asbestos? gasket is 67.5 thou thick and will not seal correctly, indeed it will probably fail if used, as the edge will be exposed and erode as the engine runs.

I have done a quick check on the barrel and the flange projects 105.5 thou, however, it appears to be a ZB barrel as the piled rifles are the engraved style and not cast. I am unsure if the flange height is different on these barrels? I have another BB barrel, and will check the flange height after work. I have yet to measure the recess in the head.

By my rough reckoning if I use a 25 thou gasket this will increase the compression by 1. In The Gold Star book on page 49 there is a chart showing pistons and compression ratios, it suggests my current piston has a compression ratio of around 7.5 to 1 and is suitable for 80 octane fuel, I was not thinking that raising the compression a little would give me fuel octane issues as the fuel available to me has a 95 Octane rating and does not have any ethanol in it.

I understand that I will need to check that there is valve to piston clearance and that I should also check the actual compression ratio as this may affect the ignition timing I use, I suspect the standard ignition timing may be incorrect for modern faster burning fuels, although this my be countered by increasing the compression ratio.

I know I have to seal the head correctly a DBD gasket looks like the solution, a side effect of correct assembly will be to increase the compression, I do not really want to alter original parts but want to build a reliable engine.

With this in mind I need to post a question on the breather system when I have time.

Thanks for giving us a better read on your skill level. There's a wide range of abilities on this forum.

The copper-asbestos gasket isn't the one you want and substituting the peeler gasket will bump up your C/R. You shouldn't have any valve to piston clearance issues from using the later gasket.

I have to back my timing off when running on 91 octane. With 100 octane race gas it's not an issue. Thank goodness for the manual control.

Hi Rudge,
The peelable gasket supplied with gasket sets is a POS
Top quality gaskets awe available from Autocycle Eng, and Pearson and maybe more GS specialists
Not cheap but you do not want to do the job a second time

John