Valve spring insulators on the exhaust side - worth fitting?

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Opinion seems fairly polarized on installing valve spring insulators (part-no: 06.7845) under the intake valve springs. I know these get shipped in packs of four and the parts manual shows they should go under ALL the springs. Like a number of owners, when I stripped my 850 Mk3 there were only insulator washers under the exhaust springs and not under the intake springs. The exhaust valve seating allows insulators to sit snugly under the exhaust springs but the profile is more dished on the intake side of which the base valve (steel seat) washer fits perfectly without an insulator washer. If you try to sneak in insulator washers underneath the exhaust side the whole assembly has no secure seating, sits too high and allows too much side movement in the assembly. What could happen if you leave the valve spring insulators off the exhaust side? Any thoughts greatly appreciated.
 
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850 heads are different. all of them get insulators. FWIW if norton did NOT modify the 850 design and left the metal in and the insulator out, they may not have cracked such a big portion of RH4 intake port heads.. RH10 are not prone to cracking...The extra metal in the port wall/roof is from 30mm ports instead of RH4=32mm
750 only on exhaust and it is to prevent overheating of the springs.
 
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Thanks Dave, so put simply, (forgive me, I’m a Luddite)… the 850 heads do not require intake washers due to the thicker walls around the aluminum casting. Have I got that right?
 
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what the heads need is the metal that the factory cut out to accomodate the insulators. modifying for insulators was VERY bad as the resulting THIN port walls crack SO easily. on RH4 heads.
insulator no insulator is a very moot point if you crack the head???? especially on the intake. The intake spring is not baked like on the exhaust....SOOOOO simple ....it was a horrible "upgrade". Now you're stuck with it and the spring pressure is now the issue.
 
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I've checked over the head and it seems fine, no cracks. It doesn't look like the valves have ever been renewed from new and the exhausts ports were very coked up. Some say you can bake your valve seals brittle if you leave the insulators off. Mine were fine without any washers on the intake side. Surly the heat from the valve guides and stems bypass the washer making it ineffective on the seals? However, I appreciate it may influence the temperature of the springs but the heat around the intake is nothing like that of the exhaust.
 
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I hope you did crack check your head? assuming RH4
Cracks are not nromally visible without a dye penetrate test which is the usual method for aluminum.
What is your head RH4 or RH10?
Did you read the RED part on my heads webpage?
 

grandpaul

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Cracks can often develop during the process of replacing guides.

ABSOLUTELY have them dye checked.
 
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I hope you did crack check your head? assuming RH4
Cracks are not nromally visible without a dye penetrate test which is the usual method for aluminum.
What is your head RH4 or RH10?
Did you read the RED part on my heads webpage?
Good question Dave... I'm not sure which head it is. How do I check, perhaps there's a number stamp on the aluminium somewhere?
 
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OK... done some digging on the http://atlanticgreen.com/nhth.htm site. It's an RH4 head with the 063807 casting number on the front bottom. Inlet valve size is D37.8mm so my guess is the ports are D32mm which points towards the head being an RH4. I'll see if I can have it dye checked. Many thanks for all your input. Highly appreciated.
 
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This is worth noting... I spoke to Andover Norton about this and they advised to leave the intake washers out. They were never installed from new and no one seems to know why the parts catalogues show them as an item.
 
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It would be good to know WHY the insulators were fitted in the first place. I would assume Norton identified some sort of heat problem that the insulator resolved. Whether machining away metal in the head to accommodate the insulator was a good idea is a different issue. ;) But they obviously were trying to fix something heat-related by installing the insulator.

IOW, leaving it out would then expose the valve train to whatever heat stresses they "fixed" with the insulator. Knowing the specifics would, IMO, lead to a more informed decision as to whether the insulator should be there or not...

Maybe they were having problems with springs getting too hot under certain operating conditions - extended idle in heavy traffic, for example, when the head gets much hotter than it does "on the road." No idea - that's just speculation.

I have always ASSUMED (!) that normal engine temps could not adversely affect the valve springs. But since I don't know anything about valve spring metallurgy, perhaps that assumption is incorrect!
 

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This is worth noting... I spoke to Andover Norton about this and they advised to leave the intake washers out. They were never installed from new and no one seems to know why the parts catalogues show them as an item.
Why would NV have the RH4 / RH10 heads machined for them if they never installed them?
I do realize when talking Norton one has to throw logic out the window, but it does make me wonder.
 

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This is worth noting... I spoke to Andover Norton about this and they advised to leave the intake washers out. They were never installed from new and no one seems to know why the parts catalogues show them as an item.
Yet AN show them and list the insulator as 4 needed to this day on the 850.
If they were left out and were machined for them that would surely lower the spring pressure on the heavier Inlet valve which might beat the lobe up a little.
 

grandpaul

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This is worth noting... I spoke to Andover Norton about this and they advised to leave the intake washers out. They were never installed from new and no one seems to know why the parts catalogues show them as an item.
Well, that's funny. I've had FOUR supposedly original MkIII engines apart, and ALL FOUR had all four insulating washers. I dutifully replaced all 4, on all four, BY THE BOOK.

(but, hey, that's just ME)
 
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Like I questioned in my earlier post: WHY did Norton put them there and...further...given that Norton installed them for a reason, why would anyone decide they know better than Norton did and omit them? ;) Unless someone here specifically knows what problem they were installed to correct AND knows what has changed that now that makes them unnecessary, they should be installed as per the service manual.
 

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I wonder if the fitting of insulators, without other changes to reduce spring pressure, is a factor in some engines high cam wear ?
 

grandpaul

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Like I questioned in my earlier post: WHY did Norton put them there and...further...given that Norton installed them for a reason, why would anyone decide they know better than Norton did and omit them? ;) Unless someone here specifically knows what problem they were installed to correct AND knows what has changed that now that makes them unnecessary, they should be installed as per the service manual.
@dynodave says it was a problem skimming the additional head material, but I've already forgotten whether he related that to the MkIII...
 

grandpaul

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I wonder if the fitting of insulators, without other changes to reduce spring pressure, is a factor in some engines high cam wear ?
That's an interesting question! However, I think more than one member has reported cam testing revealing inferior material quality.

As far as I recall I had none of the 4 (MkIIIs) that I overhauled evidence excessive wear, I'll go back and look thru my archives...
 
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