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Valve spring length

Forums

Hi

im replacing the valve springs on a 1958 99 and the Hayes manual says the length should be

outer 1.700in

inner 1.531 in

which the ones I’ve taken off are just slightly shorter(reason for changing)

i ordered a set for a 500/600 part number 06.7174 put when they arrived are 2in long

any help on which part number I should be ordering 

cheers Pete 

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Pete:

Have you asked the supplier why there is a difference?

Mike

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Hi,

I am also in the doldrums regarding which springs to use, the old ones are slightly less than Haynes 1.7" so I ordered from NOC spares pre 1960 2" long so presumably wrong, I reordered late short type post 60 which are 1.6 that are slightly shorter than my old ones, I have a problem!

If I ordered from Andover Norton reference 06.7070 would I have the correct ones ?

I would be grateful for some advice, thank you Jim

 

I too have been somewhat confused as to what is the correct length of the springs for my 1956 Dominator 99 which I assume would be the same as a 1958 99. I am in the process of rebuilding the top end of my engine and the valve springs that I have removed measure 2.084" and 1.680" respectively. I have had to return two sets of springs from RGM as the dimensions contradicted their own specifications  irrespective of their part numbers.

As I  am not going to race the bike I will probably put the springs back in the head unless I am advised otherwise. Are my springs way out of spec. ?

George  

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I am understanding the spring set differences match the cams used over any other criteria.

The "SS" 22729 twin chain cam and "1S" 06-1084 single chain cam, being the identical higher lift grind, both use the 06.7070 later springs and all the pre SS cams use the 06.7174  early springs.

http://atlanticgreen.com/camsurvey.htm

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I hadn't considered cam lift.

That could certainly effect what cam lift should be.

Mike

Hi Jim

been in touch with Andover this morning tec department very helpful say early models had longer springs and later SS models had the shorter springs.

they gave me a web site address where you can find out which cylinder head you have and from that which springs you need

mine turned out to be a later model head From an SS model after 1961

web site http://atlanticgreen.com/nhth.htm

cheers Pete 

 

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I forgot to say that the most critical thing is that the springs don't become coil-bound when on full compression.  I guess that's why the SS springs are shorter because of the higher cam lift - so you need to identify your camshaft too as it is critical.

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Attachment shows the official measurements up to 1962. Note that there are 3 versions for the Model 88 and a 4th if you include the later 88SS. 

The SS versions are stated to be 1.70" and 1.53" long and they might well have been to start with but around the end of the 70s owners started to find that new replacements that were shorter. This difference was explained as a means of preventing certain Commando cylinder heads from becoming coil-bound, on full lift, due to their exotic camshafts. I wonder how many uninformed Norton owners thought their valves springs were faulty or dying and changed them by mistake.

Also worth a mention for those who like mixing and matching cylinder head chunks, there are two versions of the spring bucket seat floating around. A thick and thinner version. Throw these into the pot of heat resisting washers...also two thickness.....and that these themselves were not fitted to all models. Then the fun can only really be beaten by dropping a collect on a very messy floor.

In reply to by philip_hannam

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Today there are only two spring set offerings as posted in earlier posts. The clear line to me is the later SS/1S cam not any particular head. The valve spring lengths chart does show different heads with different spring lengths but the NHT also had 3 different rather mild low lift cam offerings during that period and they all used the longer early style springs.

A quick look in the PS214 parts book shows the springs part number follow the cam usage and not the head. All the 21225 cam engines got the longer springs. In the PS214 suppliment the 99SS with the SS cam, though it did not get the downdraft head still got the late shorter spring set.

Exotic cam??? Obviously the 2S combat cam as used in a single chain engine (200000 series) would never be used in a twin chain motor. Even in the combat the intake insulation washer was left out as the only accomodation for that singular cam application and the late spring pack was still to remain unchanged until the end in 75.

How would anyone building a hot rod engine with an otherwise real exotic high lift cam expect a factory stock spring to work without a bit of coil bind engineering investigation?

In reply to by philip_hannam

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Oh hell. All these various thicknesses of spring buckets and washers don’t help those of us trying to build bikes from basket cases (in my case a 1960 Dommie 99). Is there a reliable (foolproof) way of identifying and getting the ‘correct’ collection of parts for a particular model and year? Are the part numbers for thick and thin cups different? Or is it just a case of trial and error? I’ve heard people talk about horror stories where the valve geometry was incorrect because of mid-matched parts - but how can the ‘average’ bike builder be sure that the geometry is correct? Is the correct geometry that critical - will the engine be harmed if it’s not correct?

Hopefully there are some experts out there who have the necessary experience and info.

Thanks

Tony

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Tony.........for the basic Model 99 you can not go wrong. Whatever thickness of spring bucket or insulation washer fitted will probably work fine. The relatilty being that most owners no longer hammer their bikes on the equivalent of 'track' day sessions so the parts fitted will be OK for the power generated.

Duff valve geometry is more likely to be caused by receased valve seats than other issues. If you are still not confident about your rebuild then ask??? There are still enough people with good knowledge about these engines.

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If I was planning on revving the nuts off an 88 with an SS cam  I would make sure I had springs that were not 50 years old and the correct length . My 99 has springs that are 50 years old ,they work fine and allow 70/80 mph cruising with no issues,I won't be fitting any doubtfull pattern replacements any time soon.

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Was introduced for cam 22729. The short spring was conceived and drawn in 1959 as far as I tell. The other thing missed in all the above is valve pocket depth, though I have not checked, some could be deeper or shallower than others. If you change something, check for coil bound - always, the MK3 Commando inlets are hit or miss if you decide to fit the insulators as per the parts book - then even the measurements from the valve seat give this away as being extremely close and you are at the luck of the tolerances being in your favour. 

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Below is hot off the RGM Press. Other spares people sell similar sets for Dominator twins.

LARGE SPRING: LENGTH: 1.650" NOMINAL (42MM) DIAMETER: 1.3" (39MM) INSIDE DIAMETER: 1" (25MM)  

SMALL SPRING: LENGTH: 1.5" NOMINAL (39MM) DIAMETER: 0.95" (24MM) INSIDE DIAMETER: 0.70 (18MM)

The depth of the cut pocket must be relative to the respective valve seat otherwise the valve guides would intrude or be too short on one side or the other.

The Dominator spring types generally fall into two distinct groups. With the short, dumpy set allocated to the SS cylinder heads and the longer, thinner versions used on the pre-SS heads (roughly before and after 1962) There is always an exception to the rules and as Dave pointed out above, in this case it is the 99SS. This had the old style non-SS Dominator head but the engine did use the SS camshaft, SS pushrods, SS valve springs and a twin carburretor bodge.

Howard, also above, is right on the button with advice......if any owner is going to take the trouble to do a full rebuild or restoration then it is a smart move to use new engine parts if there is any doubt regarding the quality or suitability of what has been removed.

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Many thanks for the re-assuring words -  the valves that are currently in the head look good (no leaks and stem tips not hammered, no ‘pocketing’), so I’ll check the spring lengths and if they are correct, I’ll re-use all the parts as they’re the original parts as far as I can tell.

Thanks again for the help - reusing good original parts makes sense. I have to admit that I tend to automatically replace engine parts as a matter of course but I’m going to re-think that strategy from now on!

Regards

Tony

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I think you boys are confused. the outer springs that I have just removed from my 88 are 2", its the inner springs that are 1.7"

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In an ideal world one should be able to quote model year, engine number and get  correct parts with the listed part numbers. However with all the modifications owners may have done and the very different supply chain we now have,  a prudent owner enthusiast needs to have a much greater understanding of how things should be and be prepared to check everything that we once could take for granted. We the owners are now often the Quality control department (but without much clout!).  We need to ride and wear out parts and have a healthy supply chain if the classic scene is to survive.

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Thanks Phil for the JPG  valve spring lengths. Hopefully will get an up date in the much anticipated new service notes to include after 60 and later 88/99/Atlas . I recently re-furbed the Atlas head and was worried that very  obvious  seat recession would have messed up the rocker action , after checking the action turned out to be really good, appart from one extra long valve wrongly supplied by the usuals .  Perhaps the the geometry  was bad when new! and corrected with the later longer valves. I suspect the spring seat poundage is lower than spec,but fine for a motor thats far too vibratory to be revved much. Plenty of room for cups and Insulator washers and an easy life for the still perfect  53 year old cam and followers.  

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Somewhere in my Service Release Notes collection is one from a long time ago informing that  replacement Norton Dominator SS (& I believe Commando) valve springs were all going to be a fraction shorter than previously. This was deliberate in order to compensate for a change to the insulating washers and spring buckets.  Unless you find some real NOS SS springs they are not going to match the numbers shown in the Little Red Book or the Big Green one.

Hi Tony

To answer re geometry you cannot do better than the great Phil Irving, his book 'Tuning for Speed' is legendry, not just for racers, but correct way to build engines.

ISBN 978-1-58850-131-8 back in print, I understand.

Chapter 3: Attention to OHV Cylinder Heads, page 42 'A valve stem of correct length has the rocker at right angles to it, with the adjuster dead central, when in the mid-lift position'.

Centralise the rocker on the v stem using shims on the rocker shaft.

Hope this helps

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Both my Atlas motors have the springs they came with. My road bike springs are now over 50 years old. There is no valve bounce under 6000RPM which it seldom if ever sees. My race engine which was built from scrap and has at times been revved to 7500 RPM does not valve bounce! This motor is putting 60BHP on the ground.

The cams are 2S in both motors. The SPRING POUNDAGE in both motors is 80-180. As it is over 25 years since they were apart I have no idea of the length. It is the poundage that matters, not the length. Fiddle about until you get the poundage right and you can't go wrong. I have no idea what other cams need to control the valves but for anything less than a "matchbox" shaped cam or over 7500 RPM (at which point the crank is likely to fail) 80-180 seems to do the trick.

 

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Nice to see I'm not the only one using lighter spring pressures, and yes, the bike has been dyno'd.

You will need to check coil bound no matter what head you rebuild with new parts and cam. As Phil points out the valve seat to pocket depth should be the same, but Norton machining accuracy in its day was not that great. This is really important with MK 3 Commando inlets where insulators are fitted under the seats, even with a standard cam it is close. They pocket depth was not deepened, so increased seated pressure and potential coil bound issues. 

There is a whole multitude of things that affect the spring travel, machining, valve stem collet recess, new valve seats. It is always worth checking if you change cam, renew valve seats etc. 

There is a x ray video of push rods at speed, it amazes me that they can take that punishment, they to act as springs. 

For those that have access to the cam drawings, then the 06.1084 will be seen as the same cam grind as that used for when the spring length change took place, the part numbers may have changed, but the cam grind is the same. To this day, what is considered the standard cam is still very good. 

 

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While we are talking cams etc,  I intend to spend some time checking over the motor .compression test, cam timing ,ignition timing.   Looking at the data it appears that although the timing graphs appear very similar  the daytona QR cam  has quite different timing figures from the SS cam. I'm wondering if anyone has  played with the  Daytona cam timing and with what result.

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Probably should be a new thread.

I am lead to believe there are 3 cams you ask about. This is my impression as a result of my research with only very little ability to handle and measure the hardware.

"daytona" seems to be very short production period Mid 50's. initial "race" cam, I have never been able to acquire a real daytona for measurement purposes or find the original part number..

"QR" originated from the daytona profile, with improved ramps PN 22125 ( I own one of these, stamped QR)

  http://atlanticgreen.com/images/cam140.gif

"SS" PN 22729 well known profile for twin chain engines carried over on single chain engines untill the MKIII  http://atlanticgreen.com/images/cam110.gif

These are both similar and would expect shifting the timing would be more affected by exhaust type and especially pipe size.

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The QR cam  is the daytona with added ramps  I understand.  At around  the same  time they added ramps I think they also changed the radius lifters to flat base  ,so plenty to consider . I am wondering about why the so  important 8 degree lead (inlet opening/Exhaust closing) of the SS cam  is not  also  important on the QR which seems to have different figures with only 2 degrees lead.Can't do much to alter that except by increasing the ex valve clearance . I suspect its more important to get max inlet lift at the right  point , whatever that is.

 

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