Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board 68-473 camshaft timing

I've just got my early A65 project built and have replaced the original camshaft with a 68-473.

I'm having trouble getting it started and want to check that I have the valve timing right. I've used the standard timing marks on the pinions which I think is right but guess that this camshaft profile may have different open and close angles from the standard?

Thanks,
Bernie

Check the amount of valve lift at TDC.If the intake is open about 1/32" more than the exhaust,cam timing is OK.

Thanks Pete, I'll check that out.

Regards,
Bernie

Hi bernie.

The standard timing on my 473 can was 20 degrees out at the crank ( 1 tooth is equal to 16.5 degrees) if you take the plugs out and slowly turn the engine over you should see both valves open fairly evenly just before tdc on the exhaust stroke when you look down the plug hole. If the inlet valve is further open then your cam is advanced by 1 tooth. The bike will run like this and still give you moderate performance. If the cam is one tooth too far retarded it might not work. I have checked to see if the valves clatter the pistons and they do not. But it might not run.

For most riding you might be better off my being one tooth advanced on the cam, it will give you more torque at the bottom end but the bike will max out at the ton. For day to day riding, this might be preferable.

Otherwise, your back to
Compression
Ignition
Carburation.

I think I've found the problem - checked valve timing using Pete and Allan's suggestions and it looks spot on. Compression is at 150 throttle closed and around 110-120 WOT. Ignition timing looking pretty close strobing at low r.p.m. with a drill and socket on the crank.

Seems it's the fuel level in the carb - I haven't worked with a Monobloc before but I did order a refurb kit from AMAL for this one and had the carb cleaned before installing all the new bits.

It seems that I need to get the right combination of old nylon needle vs brass/viton and washer/no washer under the tickler block to get the level just right.

With the old nylon needle in and no washer the level is too low - it will start with a good flood but only run a few seconds. If I keep blipping the tickler it will keep running.

With the new brass needle it floods - maybe it's too heavy for the brass float or is a bit shorter than the old one.

So next w/e I'll experiment with adjustments and see if I can get it right. At least it's fired up for the first time in around 20 years - so I'm smiling.

Thanks again,
Bernie

Bernie,
There is a wealth of info on Amals in the "British Cycles in General" forum...mostly Concentrics....and John Healy a good resource, contributes openly to carb issues. You might have another carb issue other than float height from what you have described. Is yours a two carb model?

Mr Mike

Hi Mike,

Thanks Mike, I'll check out the info you mention.

It's a single 389/217 which I don't believe was an original fit for this bike - although this is a very early Star model (Jan 62) so maybe?

I've fitted the correct jets and needle for the A65 - I'd have to check the slide but believe it's a 3.

Apart from the camshaft and 8.5:1 pistons the rest is stock.

Regards,
Bernie

Hi Bernie,

I had the same problem with a Monobloc on an A10 a few years back. The engine would only run with the tickler depressed. After checking it out I couldn't find anything wrong and whatever I did didn't help.

Eventually I cleaned it out using compressed air in every orifice I could find. That did the trick. Apparently there is an internal tunnel that gets blocked and this is the only way to reach it. Concentrate the compressed air in the vicinity of the idler jet and mixture screw.

Hope it works for you.

Beezageezauk.

I haven't been following this, but the sentence that contained the "washer under the tickler block."

Only the Monoblocs manufactured by Burlen use the washer under the tickler block. The original Monoblocs do not use a washer (gasket) under the tickler block. If you search Burlen's site you will find this information.

I am confused by the statement: "Compression is at 150 throttle closed and around 110-120 WOT." It should be the opposite: 150 WOT and 120-120 with a closed throttle. If you are not letting any air into the cylinder - throttle closed you will get a lower reading than when you let air into the cylinder - throttle open.

As mentioned above the idle carburetor must be fully functional for the bike to start and idle. The pilot jet (main jet for the idle carburetor) must be sized (per the motorcycle it is being used on specifications), clear to its proper size and fully seated in the body. The fuel/air transfer port outlet (the little hole that sits just inside the back edge of the slide) located in the Jet Block must be clean as does the air passage which passes through the jet block.

Thanks again for all your comments - carb's coming off for another blowthrough - I had it soda blasted during the rebuild and suspect that I may not have cleared it completely.

John, just been out to test the compression again with the engine (very) cold and I'm getting 150 both open and closed - reckon I got my readings muddled first time round and the sharp temp drop in the workshop has also made some difference.

I did see the article about the washer after I last posted and have now removed it. I'll check the level though as I suspect it's a little low.

Regards,
Bernie