Valve Spring Question

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Ok. So I've tried the search engine and can't find anything that really covers what I'd like to know.

After stripping down the head on my Commando I found that one inlet valve spring seat (cupped/dished washer) has a groove worn in the centre that matches the inner valve spring diameter perfectly. It's worn a ring in it .034" deep. Not something I would consider a good sign by any means. That particular spring was also showing signs of wear, well, smoothing of the spring face. I decided to replace the springs with new ones from Norvil which arrived yesterday. The new valve springs look great, but unlike most other new valve springs I've seen, the ends of the spring which seat against the spring retainer and spring seat aren't a nice smooth machined/ground finish. The have some fine marks in them, almost as if they where ground/cut to size with an abrasive cut-off disc. The engine has a Combat head fitted but still runs the original cam. I was thinking that due to the inlet valves not having the heat insulating washer under them the lack of tension may have been letting the spring chatter to some extent, but after seeing that the original springs also have this rough face surface I began to think that maybe that surface in itself was causing the spring seat wear.

Is there any merit in polishing/lapping these spring surfaces to a mirror smooth finish? Could that have been the cause of the spring seat being worn or would the lower spring tension (missing heat insulators) be a probably cause? Maybe someone with more experience in rebuilding these engines can shed some light on this for me.

Here's a photo of the new springs. It's not supremely clear as my digital camera doesn't seem to like close up shots sometimes.

Valve Spring Question


Kenny
 
That usually happens because the spring is surging and bouncing. The Combat cam is pretty hard on them due to its ramp design. Use Kibblewhite springs and you will have better luck. Jim
 
All of the part listings and diagrams I have see show "all" 4 valves spring assemblies with the heat insulating washers. I think the your issue may be unique to your situation and might be from a previous build, that is to say that it was pre existing at the point of the last build.

These spring live under a bit of pressure and is hard to imagine them bopping around unless at some time in the past the retainers dislodged. Again, hard to imagine unless the stem broke or improperly inserted.

Polishing the spring will do nothing but to show bling when the next owner/builder takes it apart.

JS also has a fine spring setup. Beehive. No inner.
 
pvisseriii said:
All of the part listings and diagrams I have see show "all" 4 valves spring assemblies with the heat insulating washers. I think the your issue may be unique to your situation and might be from a previous build, that is to say that it was pre existing at the point of the last build.

From the 063402 1972 parts list (Group 2):

"10....NM.23392....Valve Spring Heat Insulator.....(2 only on Combat at exhaust position).......4


SERVICE RELEASE
3
(AS over-leaf)
NO. N2/3
Combat valve springs.
1972 Combat engine.
Worldwide (Trade only).
On certain Combat engines from the initial production batch, we have become aware of a condition which prevents the valves opening sufficiently.

At the first service or first convenient opportunity, check that the valve springs are not preventing the valves opening fully. With the fuel tank and rocker covers removed, turn the engine until any valve is opened fully, i.e. is depressed into the cylinder as far as permitted by the valve operating gear.
At this stage push down the rocker adjuster against the valve stem, such as with an aluminium or wooden shaft, and ensure that the valve can move perceptibly as the spring is depressed further. Repeat this check on all valves in turn. Perceptible movement indicates that all is well but a lack of movement will necessitate the use of a new thinner bottom valve spring cup part number 063396. The thinner bottom cup is identified by the marking "IN" on the inner facing. As an alternative to using new cups, the existing cups NMT2073 may be reduced in thickness to 0.065i.n. (1.65mm).

The above check applies only to engine number series 200004 to 202340. Thin bottom valve spring cup washers 063396 were fitted from 202341 to 202665.
Heat insulating washers NM23392 and standard cup washers NMT2073 re-.introduced from 202666.
 
On mine, although I do not have a 2s cam, I do have a JS stage one radius type, good lift and duration but probably less aggressive on the ramping?

Some of us will have to look at the specs as see if intervention is needed.

Holy smokes, man, there's always something else, isn't there. Just when ya think you're starting to get the hang of it, lab comes around and slaps the noob badge on ya.

I do appreciate it and will wear it without shame.
 
Springs can become coil bound due to higher lift of Combat cam. Old old problem. That's why they were removed.

Also the lower valve spring cups need to have the sharp outer edges radiused when the heat resisting washers are not used so the cup sits fully down in the head instead of resting on a point contact. I think this info is on Dyno Dave's page and if not it is in the Tech Digest.
 
Well Some of us are well beyond the noob stage. My 202206 combat is the machine I first cut my teeth on in 1988 to find out about the flat bottomed spring seats I later wrote about in the Tech Digest.
Unfortunately the Norton service release may have been a well intentioned attempt, but by first hand examination of my 9000 mile bike I learned the hard way about insulation washers besides the flat spring seats. They may have been thinking the seats were too thick when in fact they did not sit on the head!!!!!!! In retrospect the service article is historically interesting but IMO obviously inaccurate due to false assumptions made at the time.
I still own the spring seats and are proudly hung on the "wall of shame" here in the shop... along with the "bent from new" combat cam.... :mrgreen:
 
Valve Spring instalation is worthy of a bit of study . Clearanceing is required on performace camshafts ( setting ) .
Worth understanding and measureing even with a std. cam. , For giving it wellie , worth setting to spec.( shimming ) .
And the Rocker shaft spacers rather than thackery washers ? .

Oil Stone to remove machineing marks .

Time spent polishing working componets mightnt impress the hoggly doggly types , but time far better spent than externals .

Set up and adjusted correctly , it wont sound to dissimilar to theis . http://www.youtube.com/watch?v=Z1InbFMA ... re=related

Why No Combat Camshaft . ?
 
That's a fair question Matt. The head was only needed as a replacement due to owners lack of diligence. He didn't secure the exhaust nuts and the left hand side thread got stripped from the original head. Because he had no real interest in "modding" the engine he didn't bother with purchasing a Combat camshaft. I still have the original head and will at some stage have it repaired, more so for the fact that I hate throwing out something that is perfectly repairable, but the engine will go back together the way I got it, with the Combat head.

After reading through some of the replies so far I think I'm beginning to see a possible reason for the abnormal wear. One that is definable with measuring instruments.

Closer inspection of the damaged spring seat shows that it has worn unevenly. One side is about .010" deeper than the other. Thanks DynoDave for planting the seeds of thought about the spring seats not actually touching the head. Being as the seat came from the inlet side (no insulating washer) I figured that maybe it had bound on the sides of the seat cavity at a strange angle instead of seating correctly against the head. To check if this theory was within the realms of reality I made a shaft which fitted the valve guide and allowed me to mount my dial gauge on it. I fitted the spring seat from the other inlet valve which is showing no wear and then checked, by rotating the shaft mounted dial gauge, whether it was seated squarely in the cavity. Measuring only the point where the inner spring would seat, I was disappointed to see that it was actually only 1 to 2 thou out of perfect. Disappointed because my theory was seeming to flounder badly. I then removed the seat washer, turned it 90 degrees and tried again, hoping to regain a sense that I wasn't just grasping at straws. Eureka! It measured about 10 thou worth of difference. Every time it was rotated and remeasured it would change again. Seeing this now in clear indications makes me believe it is more likely that the spring, operating off-axis to the direction of valve travel, may be the ultimate cause for the wear and not the spring surface at all.

To be sure that I could rectify the problem without costly machining, I tried the whole process again, but this time with a brand new heat insulator under the seat. Now, regardless of where I turned the seat around to, the readings were always within 1 thou of perfectly flat. Being as I am not going to be installing a Combat camshaft, I should have no real reason to not put the heat insulators under all four seats, should I?. Of course, during final assembly, I will be checking valve clearances and making sure there is no spring binding at full travel.

Kenny
 
Kenny,

If you are after another combat head, Bernie Porter from Porter Engineering in Maryborough has a collection that will give you a hard on for a week.

He could even fix the thread for you if you ask nicely.
 
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