BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: Rog1 on 04 April, 2021, 12:30:23

Title: M33 noisy tappets, or...
Post by: Rog1 on 04 April, 2021, 12:30:23
No matter how many times I try to adjust my tappets, there's a noisy tappet sound in the head. I've been advised to support the weight of the pushrod, via the inspection cover in the head when setting them, but it seemed to make no difference. Is there something I'm doing wrong, or could something else be the problem?
Title: Re: M33 noisy tappets, or...
Post by: Bess on 04 April, 2021, 13:03:42
Hi,
    Worth trying reducing the tappet clearance a couple of thou. Due to its age there maybe slack in the rocker arms etc.

Afterwards get the engine hot and quickly check the clearances, you'll probably find them adequate.

Best wishes...
Title: Re: M33 noisy tappets, or...
Post by: idie on 04 April, 2021, 17:03:55
It's only a couple of thou on the tappets. so long as you can rotate the rod on the follows it's usually ok.
Title: Re: M33 noisy tappets, or...
Post by: Pete C on 04 April, 2021, 17:14:06
Unless it is definitely coming from the head you could check for backlash in the cam pinions.

Turn the engine over slowly and listen for a click as the tappet runs over the cam lobe and the valve springs force the pinion round. Not sure if that explains it well but think that the lead side of the cam lobe puts tension on the springs and the springs exert force on the other side of the cam lobe so turning the pinion. Any backlash in the pinion will be heard at this point as the teeth on the cam and crank pinions meet . If there is a definite "click" then there is not much to be done to quieten the engine apart from selective assembly with different cams to reduce the backlash.

I've heard engines that sound like a sewing machine and others like a bag of nails (like my B33!)
cheers
Pete
Title: Re: M33 noisy tappets, or...
Post by: idie on 04 April, 2021, 18:48:03
If the engine is an early one it will have cams without the quieting ramps these can be noisy. Have you turned the engine over with the rocker covers off to see whether either of the valves are hanging up. Broken valve spring or a valve sticking in it's guide.
Title: Re: M33 noisy tappets, or...
Post by: Calum on 06 April, 2021, 21:27:12
Thinking outside the box slightly... valve lifter definitely clear of the exhaust rocker?
Title: Re: M33 noisy tappets, or...
Post by: Rog1 on 11 April, 2021, 19:32:49
I've been looking over the bike this weekend. I checked for backlash in the cam pinions as the timing cover was off anyway; there's none. But the noise is coming from the top end. I found the valves were moving up and down most happily when I took the covers off. Then I examined the valve lifter and found that the cable is very frayed. It had been moving quite freely until I removed it, but now I've put it all back together again the cable will hardly move at all.

I'm sure you're ahead of me here, and yes, I think the cable wasn't returning properly and was causing the lifter to just touch the rocker. We shall see what happens when I fit a new cable. If that doesn't do it, I'll try reducing the clearances. Thanks to all; I'll report back when the cable arrives from Feked.
Title: Re: M33 noisy tappets, or...
Post by: Rog1 on 21 April, 2021, 22:12:44
Calum, you were right; it was the valve lifter hitting the rocker arm. Well done, and thanks. I fitted a new cable and now all is well.
Title: Re: M33 noisy tappets, or...
Post by: Calum on 22 April, 2021, 20:31:27
Glad it all worked out.

My suggestion was from experience, I recently had the same problem on my partner's Ariel NH. The lifter was slightly binding and once removed revealed the tappet was set to an alarmingly large clearance! With the lifter fitted it felt okay... I reset the tappets and refit the lifter. Took a few goes to get the right amount of clearance before it touched the rocker arm - a much better design on the B31/B33