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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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