Hi all,

just received Valve and Valeve guides from NOC.
Sadly one wronge Valve in the shippment. Anyway, her is what I need to know.

I measured the Guides and the Shaft of the Valves, I have 0,04 mm difference between bore and shaft diameter. As I remember from other engines this is fare to much.
I dont have any experience with SV Engines but I am affraid stuff could leak through the "Gap" between guides and Valve shaft during use.

Does anyone know what the max difference between the two parts could be and could let me know if I can insert the guides into the Cylinder. I thougt NOC is sending NOS Parts so the bore diameter shall be correct.

Thanks
Phillip

email (option): phillip.thaler@gmx.at

Usually the side valves run pretty slack in their valve guides, it seems that is to stop them jamming in the guide when they have carbon on them, I presume that you are talking about the movement in the head of the valve at about half way down the valve, this would seem about normal play, but if you mean the difference between the valve guide internal measurement and the stem this would seem excessive

email (option): davmax@ntlworld.com

Hi,

I am not that safe in using engine terms in english so I have added a drawing. Hope this could clarify the situation



Thanks Phillip

email (option): phillip.thaler@gmx.at

Hi, that equates to 0.0016" so I think you'll find that is about the correct measurement. The valves on side valves always seem to run a little bit slacker in their guides, probably as they don't have any positve means of lubrication

email (option): davmax@ntlworld.com

For BSA’s, the Bruce Main-Smith booklet says that stem-to-guide clearances should be 3-4 thou for inlet and 4-5 thou for exhaust. That’s 0.08-0.10 mm inlet and 0.10-0.13 mm exhaust, which is much larger than the Norton figures above. Does anyone have an explanation for the difference?

ChrisJ

I wouldn't imagine such a tight clearance is correct for a Norton..More likely that the guides should be resized after fitting. I'm sure someone more familiar with the Norton may provide the correct tolerances.
As far as the M20 is concerned I am on firmer ground and have experimented with reducing the standard tolerances.
The result is a high likelyhood of valve siezure and I wouldn't recommend it unless the valve guide material is changed to a suitable high silicone bronze. There are some grades designed for use in high temperature, low lubrication environments....Ian

email (option): ian@wright52.plus.com

The Norton WD manual gives a valve stem diameter of .343"

Needless to say, they don't mention the guide ID !

Measuring NOS items, I can confirm the stem OD and arrive at a tight .347" for the guide using the digital vernier.

.004" (0.10mm)seems to comply with BSA practice.

Thanks Rik..Has a Norton 'standards book' turned up yet?....Ian

email (option): ian@wright52.plus.com

Sorry Rik..I had forgotten about the 'generous' Norton production tolerances... ..BSA standardised production tolerances for component interchangeability in 1864 for the manufacture of guns...in fact that was why the company was formed....Ian

email (option): ian@wright52.plus.com

Hi Rik, I've just bought some new valves from Russell's and they measure .340" (my old valves are .339")and my old guides measure .344" and .3435"
Still the same clearance but worrying that the book says the valves should be .343"..?

email (option): horror@blueyonder.co.uk

Thanks Guys for the answers.

email (option): phillip.thaler@gmx.at

The 'Radco' book has some pages from a Tranco valve catalogue which lists valve dimensions in fractions. The only valve with the PG/T (Parallel Groove / Taper) that fits in with the manual are 11/32" stems(.34375" - 8.73mm). The guides unfortunately also seem to be referred to as 11/32" so the clearance is not given.

The Tranco catalogue doesn't show distance from tip to collet groove and this varied between the 1937 and 1938 type engines.

Quite frankly, it's a difficult area unless someone has a book with a full list of applications.

When was your vernier last calibrated ?

Get out a micrometer...A Vernier does not measure with the required degree of consistency. In Engineering the Vernier is only expected to produce a reliable accuracy of + or - a thou at best.
Is there anything on the Norton website covering valve guide clearances..surely we haven't got this far without someone knowing this?....Ian

email (option): ian@wright52.plus.com

A further search of Franks' 'Practical Guide' states in reference to both sv and ohv models: "When new, there is 0.002 in. to 0.003 in. clearance so there is bound to be a certain amount of rock".

Let's Rock !

I've just taken my new, and original valves to my engineers, and he's measured them with a micrometer.
My original valve is 0.340" all the way along the stem so there's no ware on it at all.
The new valve from Russell's measures 0.342" the bloke was very impressed with it as it's stainless steel plasma nitrated and frictionless compared to the original, so can run at a closer tolerance. He couldn't believe they were only £15 each.
I didn't take my barrels to him but I will at the end of the week when I beat him with a big stick to get my crank cases finished..!

So yes, my verniers are rubbish as they were out by a thou or 2, but the original valve still measures 0.340"

email (option): horror@blueyonder.co.uk

The stems of my new valves (from Jacob de Groot) measure uniformly 8.845mm = .3482"
The exhaust valve drops in its seat with a 'clunk', and has a very slight sideways movement - some .2mm - when raised a bit.
The inlet valve goes down slowly but surely, and has no sideways play, so I think some careful reaming of the guide is in order !

email (option): viaconsu # planet dot nl

Is that for a Norton 16H..?

email (option): horror@blueyonder.co.uk

M20 of course ! My one and only...

email (option): viaconsu # planet dot nl

I knew I’d come across it somewhere but it’s taken me a while to remember (no change there, then!). There’s a simple formula for calculating stem-to-guide clearance from how much the valve head “rocks” from side to side when lifted off the seat.

Clearance = (R x G) / (2L + G)
where
R is the total amount of side-to-side Rock
G is the length of the valve Guide
L is the Length from the (closest) end of the guide to your measuring point (e.g. the valve head).
Choose any measurement units you like (inches, thou, mm, fathoms), just as long as you are consistent throughout. To check for uneven wear or a bent stem, you should measure the rock back-and-forth as well as side-to-side, and repeat a couple of times after rotating the valve.

I haven’t used the formula myself before, so let’s try it on Hans’ measurement.
For BSA M20 exhaust
G = 3-3/8” (I think) = 86 mm approx, and
L = 15/16” (about 24 mm) when the exhaust valve is on the seat. Let’s say Hans raised it about 1 inch or 26 mm, and use L = 50.
The valve head rocked 0.2 mm (each side of centre, I assume) so R = 0.4 mm.
Plug it into the formula and you get clearance = 0.18 mm or 0.0047 inches, which is near ideal. A bit rough and ready, but it seems to work.

ChrisJ

Hi Chris..Well I've never come across that one before...fascinating. Any background on when the formula was...er...formulated...and by who?...Ian

email (option): ian@wright52.plus.com

Chris

are you sure it shouldn't be
C=RxG/2x(L+G)?
That would come from equivalent triangles
C/G = (R/2)/(L+G)
It's been a long day, i hope i am thinking straight.

cheers
Iain

I have to admit that I quoted the formula blindly and didn't attempt to check it (geometry was never my strong point anyway) so I'm in no position to argue with you. I quoted from John Robinson's Motorcycle Tuning (Four-Stroke). Will try and find another reference in order to clear the matter up.

ChrisJ

My head hurts, but I'm beginning to appreciate my investment in micrometers and small hole gauges... ...Ian

email (option): ian@wright52.plus.com

I haven’t found a good reference although there’s a bit of Internet chatter on the subject. All I can say is that the formula I quoted looks right, noting that if you were to measure the valve rock very close to the guide then L = 0 (approximately) and the formula simplifies to Clearance = R, which is what you’d expect.

Anyway, I’ll take the hint and go buy some small bore gauges!

ChrisJ

I've just received 2 NOS 16H valve guides from Russell's and taken them and the new and old valve along with my barrels to be measured correctly with a small bore gauge and a micrometer. These are the results;

Both new guides = 0.344"
My old valve = 0.340"(0.3405) (all along the stem so no wear)
New stainless valves = 0.3415"(0.342)

My old guides in the barrels are,
0.345" Exhaust
0.347" inlet

I will leave the exhaust guide in and just change the inlet guide.

There is a great difference in the feel of the old valves in the new guides (without oil) compared to the stainless plasma nitrated valves. The stainless valves slide very easily even though they are a tighter fit.

email (option): horror@blueyonder.co.uk

So looking back now at Phillips original question, I would say that the valve measurement of 8.63mm is just under 0.340" so is just under my original valve measurement.
Phillips new valve guides are 8.68mm that's just under 0.342" which is 2 thou tighter than my NOS guides, leaving a 2 thou clearance. I would say that was ok..?

email (option): horror@blueyonder.co.uk

Hi Horror..I would have my doubts at a .002" valve stem to guide clearance without definite confirmation....The M20 has a valve stem/guide clearance of .003"-.005" (in. and ex.).
To achieve this clearance it is nearly always necessary to size the guides after fitting to the barrel. Clearance 'off the shelf' is generally under these figures and occasionally a valve won't enter the guide.
The stipulated M20 clearances are for an engine that also has at least a partial supply of oil to the guides..they are lubricated by pressurised oil mist from the crankcases. The Norton relies on the periodic application of a grease gun.
I have tried closing down the clearances in an M20 in an effort to control better the centrality of the valve to its seat when closing and to quieten things down...the result was that the exhaust guide nipped up on the valve.
I have successfully closed the clearances to .0015" by replacing the guides with a low expansion silicone bronze type but the material was very expensive.
Frankly I am puzzled that there isn't a forum member who owns a rebuilt 16H or Big 4 that has this information to hand..or at least a clearance arrived at by experimentation and experience..Maybe it would be worth a phone call to Dr. John the well known Norton eccentric..er..I mean expert...
....Ian

email (option): ian@wright52.plus.com