650SS valve spring preload

Previously wrote:I rebuilt my 650SS engine with new PW3 camshaft, tappets, valves, valvesprings, valve guides and tappet adjusters (Andover parts).After about 700 miles the top of the shaft of my new inlet valves are badly worn in (because of tappet adjuster) and someguys told me it is because of too strong valve springs. Please couldanyone tell me the correct valve spring preload (at the position when the valve is starting to open) for my Dominator 650SS (year 1962) and my Dominator 88 (year 1962).I have measured following values:

• Norton 650SS (downdraught head, pw3 camshaft):- with Norton Andover valve springs (part no. 6-7070) valve opens at 88 lbs (40kg)- with NOS Terry's valve springs (for 650SS/Atlas) valve opens at 83 lbs (38 kg)
• Norton Dominator 88 (standard alloy head, standard camshaft):- with springs fitted from previous owner valve opens at 66 lbs(30 kg)

Hello Roland,

I'm sorry; but I can't answer your question, regarding the correct valve spring preload.

There is something wrong to make the adjusters wear pits in the valve stem tips. Especially in such a short time. Excessive valve spring tension would be a reasonable guess; but Iâd like you to consider some other possibilities.

It is worth bearing in mind that the PW3 camshaft has a similar maximum lift to the old (Combat) 2S camshaft.

One of the problems raised when the Combat engines were introduced, was that at full lift the valve springs didnât have sufficient range of movement and became coil-bound.

It doesnât matter how soft your spring pre-load is then, because when coil-bound the spring is no longer a spring, itâs not going to compress any further. Then the pushrods will certainly have to flex a bit; the rocker arms will be stressed, the camshaft lobes will wear and cam bushes will start to wear oval.

A solution from Norton was to machine the grooves for the valve collets 1/16â higher.

Do you have access to one of the 70âs Paul Dunstall tuning booklets? Inside there are a few paragraphs with illustrations, explaining how to adjust the valve springs until they all compress evenly. Paul Dunstall used to recommend setting them to 0.045â from coil-bound (other people say 0.060â). Talk it over with âthe guysâ.

If you use the same techniques as in the booklet, you could at least measure whether or not your valve springs have any movement left at full lift.

Another factor with your valve wear could be the suitability of the valve stem material and whether (or not) the stem tips were hardened, most often Stellited.

For the adjusters to wear into the valve stems (without the coil-binding problem) after 700 miles, I think the hardness of the valve tops is suspect.

A lot of owners have had the same experience, especially with Commandos. Some American enthusiasts swear by fitting hardened caps over the valve stem tips. They call them âlash-capsâ and fitting them will involve machining the valve stem tips to maintain the rocker geometry (90 degree angle between rocker shaft and valve stem when the cam is at ? lift). Shortening the push rods is another method.

There is quite a lot of concern amongst long term Norton owners about the quality of components now being marketed as âoriginal equipmentâ by most of the main parts suppliers (including Andover). These businesses are all run by very nice blokes (or lasses) of course; but some of the Mickey Mouse components being offered as Norton OE are just not good enough.

If the valve stem material you have is suitable for Stellite and you make sure your springs are not coil-bound at full lift, some machining of the valve stem tips and re-hardening may be the way to go. Otherwise, look for some better quality valves.

It would be interesting for everyone here to know how you get on with solving it, as well as what you find out along the way.

Good luck.

Paul

• Norton 650SS (downdraught head, pw3 camshaft):- with Norton Andover valve springs (part no. 6-7070) valve opens at 88 lbs (40kg)- with NOS Terry's valve springs (for 650SS/Atlas) valve opens at 83 lbs (38 kg)
• Norton Dominator 88 (standard alloy head, standard camshaft):- with springs fitted from previous owner valve opens at 66 lbs(30 kg)

Hello Roland,

I'm sorry; but I can't answer your question, regarding the correct valve spring preload.

There is something wrong to make the adjusters wear pits in the valve stem tips. Especially in such a short time. Excessive valve spring tension would be a reasonable guess; but Iâd like you to consider some other possibilities.

It is worth bearing in mind that the PW3 camshaft has a similar maximum lift to the old (Combat) 2S camshaft.

One of the problems raised when the Combat engines were introduced, was that at full lift the valve springs didnât have sufficient range of movement and became coil-bound.

It doesnât matter how soft your spring pre-load is then, because when coil-bound the spring is no longer a spring, itâs not going to compress any further. Then the pushrods will certainly have to flex a bit; the rocker arms will be stressed, the camshaft lobes will wear and cam bushes will start to wear oval.

A solution from Norton was to machine the grooves for the valve collets 1/16â higher.

Do you have access to one of the 70âs Paul Dunstall tuning booklets? Inside there are a few paragraphs with illustrations, explaining how to adjust the valve springs until they all compress evenly. Paul Dunstall used to recommend setting them to 0.045â from coil-bound (other people say 0.060â). Talk it over with âthe guysâ.

If you use the same techniques as in the booklet, you could at least measure whether or not your valve springs have any movement left at full lift.

Another factor with your valve wear could be the suitability of the valve stem material and whether (or not) the stem tips were hardened, most often Stellited.

For the adjusters to wear into the valve stems (without the coil-binding problem) after 700 miles, I think the hardness of the valve tops is suspect.

A lot of owners have had the same experience, especially with Commandos. Some American enthusiasts swear by fitting hardened caps over the valve stem tips. They call them âlash-capsâ and fitting them will involve machining the valve stem tips to maintain the rocker geometry (90 degree angle between rocker shaft and valve stem when the cam is at ? lift). Shortening the push rods is another method.

There is quite a lot of concern amongst long term Norton owners about the quality of components now being marketed as âoriginal equipmentâ by most of the main parts suppliers (including Andover). These businesses are all run by very nice blokes (or lasses) of course; but some of the Mickey Mouse components being offered as Norton OE are just not good enough.

If the valve stem material you have is suitable for Stellite and you make sure your springs are not coil-bound at full lift, some machining of the valve stem tips and re-hardening may be the way to go. Otherwise, look for some better quality valves.

It would be interesting for everyone here to know how you get on with solving it, as well as what you find out along the way.

Good luck.

Paul

To the site administrators/Moderators:

Re my message sent at Sunday 11:55.

With my varying & unreliable (TalkTalk) broadband, I repeated the pasting of my message when it didn't seem to work the first time.

Would you kindly edit it please, so that it does not contain a duplicate.

Thank you.

Paul

Dear Roland,

It is all to do with the lack of hardness on the ends of the valves. I had a similar problem with my 650ss about 5 years ago and it is down to the quality of the valve - quite simply they are not correctly case-hardened resulting in the tappet head simply hammering away at the top of the valve.

Change the valves for a better quality component and the problem will not occur again. Hard part is trying to ascertain what the valve quality is upon purchase - are your old valves suitable for re-use?

Mit freundlichen Gruessen

Peter Bolton

A friend of mine ground the end of his valves down to take 250 Ducati lash caps, that fixed it. And if I wanted to know how to set up a PW3 cam it would certainly make sense to ask the supplier???

I know Norman White sells them and he will tell you how to set them up. I bought some of these cams from him and he said he just used the latest standard Commando springs for them. He said any stronger spring was not needed and in fact would cause more problems while solving none!