BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: Starphil on 29 January, 2018, 16:32:34

Title: Scavenge Valve Replacement
Post by: Starphil on 29 January, 2018, 16:32:34
Hi,
My Starfire has a lot of il in the sump. looking at the scavenge valve it's difficult to see if it's working ok. The end of it looks a bit chewed up so i would like to get it out and inspect it and if necessary replace it but how do you get it out? Iv'e seen reference to a grub screw but can't see one.

Has anyone done this?

Cheers
Phil

Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 29 January, 2018, 17:42:06
I believe it is just an interference fit but you would probably need to heat up the casing around it to be able to pull it out. I think I've tested one before now by putting a tight fitting rubber pipe over the end and then sucking and blowing to check whether the valve is working ok.
Title: Re: Scavenge Valve Replacement
Post by: Starphil on 29 January, 2018, 18:05:37
Thanks for responding.

The engine is still in the bike so I'll have to have a think about how I might heat that bit up.

Cheers
Phil
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 29 January, 2018, 19:43:51
Just re-reading your original post again, I think you are looking at the wrong non-return valve (NRV). There are two inside the engine, one on the feed side and one on the return side. You have been looking at the return (scavenge) NRV which doesn't really do a great deal. It is the feed NRV which is there to help stop oil in the oil tank draining into the sump and a problem with it can result in wet sumping. On your engine, it is located in the inner timing cover and there is a grub screw that has to be removed to get at it. Therefore, it is a bit of a job to overhaul the feed NRV but it depends on how bad your wet sumping is.
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 29 January, 2018, 19:51:30
Feed NRV is shown with part nos 20, 21 & 23.

Title: Re: Scavenge Valve Replacement
Post by: Starphil on 29 January, 2018, 19:59:30
It's been 2 - 3 weeks since I ran it and today when i took the sump cover off (because there's a leak) about half a pint came out.

Also, when I did have it running it was OK at idle but smokey when revved. Hoping this is just because of oil in the sump.
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 30 January, 2018, 06:43:06
About 1/2 pint isn't too bad and shouldn't cause any problems when you start the bike - the excess oil will quickly get pumped back to the tank. Unfortunately, the smoking is more likely to be due to worn piston rings or valves.
Title: Re: Scavenge Valve Replacement
Post by: Starphil on 30 January, 2018, 10:29:29
That would be a shame if it is.

The bike hadn't been run for a 2 -3 years prior to me buying it at the end of October. Since then I've been sorting out a few minor things so it has only been started a few times. I'll have to see how it goes when I give it a longer run.
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 30 January, 2018, 11:36:32
If it hasn't been run that much it might simply need to bed in again and to burn off anything that accumulated inside the exhaust system!
Title: Re: Scavenge Valve Replacement
Post by: Starphil on 27 March, 2018, 10:23:01
I've wrestled the engine out of the bike in order to fix an oil leak on the inner timing cover and to get a good look at the scavenge valve. I can now see that the valve is stuck in the open position and it looks like someone has tried to remove it in the past. It has a thread in it but most of the end that would sit it the sump is chewed up.

I've tried fitting a bolt, heating it up and pulling it out with a slide hammer, all without getting it to budge. So it now looks like I'll have to drill it out and obviously don't want to damage anything but I don't know how long it is or how the spring and ball bearing is held in place. Has anyone got any decent pictures of one or any experience of drilling or cutting one out?

Cheers
Phil
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 27 March, 2018, 10:59:52
Phil.  Can you post a picture of what the end of the pipe looks like - the main requirement is that it should poke down through the gauze filter so that oil is sucked back to the oil tank from beneath the filter.

As previously indicated, this valve does not do very much but the ball should at least move up and down freely. I would leave the pipe well along unless it's badly damaged or is stopping the valve from working. I believe it's an interference fit in the crankcase but you would need to apply a lot of heat around the pipe to expand the aluminium sufficiently and then find a way of gripping the pipe tightly enough in such a way that you don't damage it.
Title: Re: Scavenge Valve Replacement
Post by: Starphil on 27 March, 2018, 11:36:29
When I got the bike there was no gauze filter in the sump and the end of the pipe was damaged. It had some of the end missing and what was left had a split in it. I fitted a mesh and new gaskets. However, as i said now that I've got the engine on the bench I can see that the ball bearing doesn't move and it looks like a piece of the spring has got past it.

There was never enough pipe to get hold of to pull it out and my attempts the remove it have certainly added to the damage and the end of the pipe where it was split has broken off. So it definitely has to be replaced now :(

Following your earlier reply I checked the other non-return valve and it appeared to be ok.

I think that the presence of the thread on the inside of the valve means that someone has either had this out or attempted to get it out in the past.
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 27 March, 2018, 13:01:20
As far as I'm aware, there isn't a spring in this NRV - it normally closes by the ball falling down under gravity. It sounds as though you might have some foreign matter in the valve which might be what's keeping it open.

If the pipe has to come out, then you would need to find a way of effectively attaching a suitable rod to it so that you can then rig up a slide hammer to pull it out, if necessary. Options for attaching the rod could stretch from soldering to tapping a thread on the end of the rod and inside the scavenge pipe.

Where are you based? I would be happy to help if I can.
Title: Re: Scavenge Valve Replacement
Post by: JulianS on 27 March, 2018, 13:21:35
I think what you may see as a bit of spring is just the wire which stops the ball dropping out.

Illustration from workshop manual.
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 27 March, 2018, 13:56:14
Here's what the scavenge valve actually looks when removed from the engine. It is possible to buy a replacement valve.

Title: Re: Scavenge Valve Replacement
Post by: Starphil on 27 March, 2018, 14:49:24
Thanks for the pictures. On mine the protruding part of the pipe was less than half of that and had no angle on the end.

The good news is that I've managed to get it out without drilling it. A combination of heat, cold and a good twisting with a screw extractor and eventually out it came. Before that the ball bearing popped out together with what looked like a combination of a spring and silicon.

Anyway, I've ordered a new one. In the meantime I will get on with some other bits and pieces including giving the engine a good clean and polish while I've got it on the bench.

One other decision that I've got to make is what to do with the wheels. The chrome on them has some rusting and the spokes are pretty shabby. Any recommendations welcome.

Thanks for all of your help.

Cheers
Phil
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 27 March, 2018, 16:50:32
Well done in managing to extract the valve. I've never had the need to remove one before but I also ordered one earlier just to get a better idea of what it actually looks like.

In terms of the wheels, it's almost impossible to smarten them up once they start to rust. However, they are expensive to replace. I recently paid 375 to Central Wheel Components for a set of S/S rims and spokes for a C15 - getting them to do the rebuilds would probably have added another 180.
Title: Re: Scavenge Valve Replacement
Post by: ROYC on 27 March, 2018, 18:30:16


One other decision that I've got to make is what to do with the wheels. The chrome on them has some rusting and the spokes are pretty shabby. Any recommendations welcome.

I am very happy with my stainless rims and spokes.
Title: Re: Scavenge Valve Replacement
Post by: Starphil on 27 March, 2018, 21:34:32
Where did you order your valve from?
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 28 March, 2018, 07:51:54
CCM Britain for about 10 including P&P. It was cheap enough and I was curious to see what it looked like internally as it's not something that usually gets taken apart.
Title: Re: Scavenge Valve Replacement
Post by: AWJDThumper on 04 April, 2018, 15:35:53
My scavenge valve arrived today. Basically, the bottom half consists of a tube which is smaller in diameter than the ball bearing while the top half consists of a tube which is much wider than the ball bearing. The ball bearing is retained in the wider tube by a ~1mm bar through the top of the valve which can just be seen in the pic. The bore is blocked when the ball bearing falls down under gravity and is opened by the oil flow sucked up from the sump by the oil pump.