The BSA A7-A10 Forum

Technical => Frame => Topic started by: t20racerman on 17.08. 2019 19:45

Title: Rubber mounted head steady
Post by: t20racerman on 17.08. 2019 19:45
Hi all

I was inspired some time ago to make my A10 head steady rubber mounted - inspired by Chaterlea25's post about the one he made:

https://www.a7a10.net/forum/index.php?topic=2912.0

As he said in that thread, without a doubt the original head steady mounting of the rockerbox cover to the frame contributes greatly to rocker cover joint leakage, due to shear stresses between the head and rocker cover. As I'd just re-torqued the head after a rebuild, and had fitted a new SRM rocker cover gasket, I didn't want to fit the original steady and have leaks again.

I've photographed the steady I made, and although nowhere as neat as chaterlea's one, it does the job. I was going to make a neater one, but this is version 1 - a quick, simple and easy method that I did to test the concept. Its done 800 miles so far (and I ride & rev my bike hard) and its worked well, with no leaks (yet?) - although it has to be said that the Bunn valve breather system that I fitted (described elsewhere on this forum) made a huge difference too.

I race a TZ350 that has rubber mounted engine fittings, and have used these rubber bushes on my T20 Suzuki Classic racer too, (see www.t20suzuki.com (http://www.t20suzuki.com) for details), to rubber mount its engine to stop frame cracking and reduce vibrations. The Yamaha part number is 102-22123-00 if anyone wants one.
I took a used one of these out of my T20 frame and welded two mounts to it, as shown in the pics. Obviously this melts the rubber, so I had most of the rubber mount in water whilst welding it, then cooled it v quick. As I said, this is version 1...

I'll probably make a holder for the bush if I ever redo it (see my T20 page for an idea of what I mean), but this worked, and its still working well today, 800 miles later.

For those worrying about a 'steady' that moves, the actual movement is minimal, but more importantly it damps the vibrations down by a large amount, giving the rocker/head gasket joint a much easier time. The engine itself remains smooth and vibrates no more than it ever did.

Adrian




 

Title: Re: Rubber mounted head steady
Post by: TT John on 19.08. 2019 09:22
I like that idea and think I may try it myself, although I'd never really thought about it before, I know the Sunbeams had rubber mounted engine supports, it must be a help to cut down the vibration.

Regards TTJohn
Title: Re: Rubber mounted head steady
Post by: duTch on 19.08. 2019 11:06

 Looks like a isolastic/silentbloc swingarm bush- maybe a better use for the dodgy ones I've read about (but never been involved with) than trying to fit them where they were 'intended' ... *dunno*
Title: Re: Rubber mounted head steady
Post by: cyclobutch on 19.08. 2019 14:03
Accepting the concerns over a rigid head steady being likely to accelerate onset of rocker cover leaks, I don’t see that there can be much/any difference between having a rubber mounted steady and none at all. It’s not going to hold the engine still is it?
Title: Re: Rubber mounted head steady
Post by: t20racerman on 19.08. 2019 15:02
Accepting the concerns over a rigid head steady being likely to accelerate onset of rocker cover leaks, I don’t see that there can be much/any difference between having a rubber mounted steady and none at all. It’s not going to hold the engine still is it?

Hi cyclobutch
I know it sounds like that, but these bushes barely move. They just move enough to have the rubber damp out the vibrations. Hence, the head is held steady, with just a tiny bit of motion, unlike the motion it would have if it had no steady at all. A bit like how cricketers bat with 'soft hands' if they want to take pace off the ball. The reduction in shear stress between the head and rocker cover is significant.

I rubber mounted my T20 Suzuki classic racer using these bushes and having done the job, was disappointed at how tiny the motion was when you revved the engine - You could feel it, but not see it. I thought I'd wasted my time, but the bike vibrated much less, and more importantly the frame and engine casings stopped cracking - as they had repeatedly before then. Its definitely worth considering if you are plagued by the dreaded rocker cover leaks..

Adrian
Title: Re: Rubber mounted head steady
Post by: RoyC on 19.08. 2019 17:30
Has any one worked out how to rubber mount the rest of the engine ?
Title: Re: Rubber mounted head steady
Post by: chaterlea25 on 19.08. 2019 18:31
Hi All,
T20,
Those bushes would seem ideal for the job
Rather than weld directly on to the bush outer with the risk of damaging the rubber
I think a steel tube that the entire bush could be pressed into it could have the "legs" welded to it before pressing in the bush?
John
Title: Re: Rubber mounted head steady
Post by: RoyC on 19.08. 2019 19:37
Hi All,
T20,
Those bushes would seem ideal for the job
Rather than weld directly on to the bush outer with the risk of damaging the rubber
I think a steel tube that the entire bush could be pressed into it could have the "legs" welded to it before pressing in the bush?
John

Or try to press the rubber out of the outer tube, weld it, then press back in, with the help of silicone grease.
I have ordered one to try it.
Title: Re: Rubber mounted head steady
Post by: chaterlea25 on 19.08. 2019 22:53
Hi Roy
Those bushes will have the rubber bonded to the steel

John
Title: Re: Rubber mounted head steady
Post by: Rocket Racer on 20.08. 2019 06:05
Has any one worked out how to rubber mount the rest of the engine ?
This is the crux of the matter, a rubber mounted engine, no worries; but rigid engine mounts and reducing the stiffness of the head steady is not something I would personally not do (but I'm no engineer).
A poorly balanced and or thrashed pre unit A10 can break head steadies and the frame and engine lugs (been there - all three on a motor running to 7500), so my personal opinion is they all need to do their bit together and a rubber headsteady partially compromises one link.
I do agree the original design is compromised, it should mount to directly the head like a semi unit does, albeit that connects to the frame in a poor location. the norton twins got round this by not having a separate rocker box and the BSA assumption is the load transfers via the studs, but in practice as the rocker box gasket settles the head steady can fret the rocker box join.
These bikes have their weaknesses and create endless debate looking for solutions. My race a10 has a seriously beefed up rocker mount and I keep everything religiously tight and it might weep but it doesnt leak and has stopped breaking the frame
Title: Re: Rubber mounted head steady
Post by: t20racerman on 20.08. 2019 06:51
Hi All,
T20,
Those bushes would seem ideal for the job
Rather than weld directly on to the bush outer with the risk of damaging the rubber
I think a steel tube that the entire bush could be pressed into it could have the "legs" welded to it before pressing in the bush?
John
Hi John

That is what I was intending to do, and indeed did do when rubber mounting my Suzuki T20 race bike engine. On the T20 each of the 4 rubber bushes is in a tight fitting 'top hat' tube that is welded to the frame. It works very well indeed.
I'll upgrade the one on my A10 sometime, but this 'version 1' (welded legs direct to the bush) has worked well so far - a kind of proof of concept :-)

Adrian
Title: Re: Rubber mounted head steady
Post by: Greybeard on 20.08. 2019 09:19
Is it not possible to fit a steady on cylinder head bolts?
Title: Re: Rubber mounted head steady
Post by: berger on 20.08. 2019 11:42
rocket racer I think you might try a longer bolt to nylock nut fitting *wink2*
Title: Re: Rubber mounted head steady
Post by: Rocket Racer on 21.08. 2019 04:06
rocket racer I think you might try a longer bolt to nylock nut fitting *wink2*
I knew someone would pick that up  *doh*, this was the inital fitting down at the engineers, after I'd broken the frame, several engine mounts and head steadies.
I also had it balanced for higher revs and it hasnt failed since.