seizing valves

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Chris Berry
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seizing valves

Post by Chris Berry »

The saga with my 51 G80 engine continues. Having just completely rebuilt the engine and replaced both valves and guides (done by an engineering works) I firstly seized the inlet valve after 28 Miles. Took the head back to the engineering works who refitted the valve and increased the guide clearance. Put it back together and after a further 20 miles seized the exhaust valve. Checked the obvious, presence of oil on the rocker gear, rocker gear free. All seems OK. Even rechecked the oil gallery for the inlet valve (this was blocked when the inlet valve seized). The engineering works is a professional workshop but I can only assume that the G80 requires a lot of valve guide clearance. Can someone advise if this is the case. I can only hope that I haven't bent the valve (I heard it hitting the piston) and it can repaired (I won't be removing the head to look until tomorrow having had to push the bike about three miles home I was to tired)
SPRIDDLER
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Re: seizing valves

Post by SPRIDDLER »

What rotten luck. :cry:

Were the valves and guides from a regular parts source, e.g Club spares or AMC Classic?
The guides should have a circlip to prevent them from being inserted (or dropping) too far in towards the combustion chamber and therefore overheating (zorst) or clashing with the valve head.
As you probably know the oiling hole in the side of the guides needs to line up with the oil transfer gallery in the rocker box casting.
Is the inlet valve metering screw open around 1/6th of a turn?

I don't have tech info for valve to guide clearance to hand for a 500 but I would expect the clearances to be very similar to the 350. Below are the figures for the 350 which may give you a rough clue.

First dimension column (High/Low) gives the dimensions as manufactured. Second column is with acceptable wear. Third column is the condemned wear level.

Image

In short, the clearance when new for the inlet is 2.5 to 3.0 thou., (zorst 3 to 5), acceptable clearance 5 thou., (zorst 7) and condemned when clearance exceeds 10 thou. (zorst 12).
If I find the figures for the 500 I'll update.
'There is a tide in the affairs of men
Which taken at the flood............'
Chris Berry
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Re: seizing valves

Post by Chris Berry »

Thanks Spriddler,
the valves and guides were supplied by AMOC so I wouldn't expect a problem with them. After I seized the inlet valve I increased the restriction screw out to 2 turns figuring a little blue smoke would not hurt while it was running in. I can't think of any other reason the valves would seize except for insufficient clearance. I will print out the info you gave me and take it to the engineer. Where did you get this info from?
SPRIDDLER wrote:What rotten luck. :cry:

Were the valves and guides from a regular parts source, e.g Club spares or AMC Classic?
The guides should have a circlip to prevent them from being inserted (or dropping) too far in towards the combustion chamber and therefore overheating (zorst) or clashing with the valve head.
As you probably know the oiling hole in the side of the guides needs to line up with the oil transfer gallery in the rocker box casting.
Is the inlet valve metering screw open around 1/6th of a turn?

I don't have tech info for valve to guide clearance to hand for a 500 but I would expect the clearances to be very similar to the 350. Below are the figures for the 350 which may give you a rough clue.

First dimension column (High/Low) gives the dimensions as manufactured. Second column is with acceptable wear. Third column is the condemned wear level.

Image

In short, the clearance when new for the inlet is 2.5 to 3.0 thou., (zorst 3 to 5), acceptable clearance 5 thou., (zorst 7) and condemned when clearance exceeds 10 thou. (zorst 12).
If I find the figures for the 500 I'll update.
SPRIDDLER
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Re: seizing valves

Post by SPRIDDLER »

It's from the Army Workshop Handbook of Inspection Standards for the WD G3L from 1941 to 1953 which you will find in Christians Archives:

http://archives.jampot.dk/book/Workshop ... ndards.pdf

It's (probably the only) comprehensive and condensed information available in one document for tolerances and clearances apart from random figures that can be found buried in the multitude of Owners and Workshop manuals available, although I've never found valve/guide clearances anywhere else.
Whilst it's for a 350 and the 500 probably has larger dia. valve stems and guides I would suggest that the running clearances are a valid guide for your 500.......... e.g. similar materials, function and operating temps.
(I've just given a pal my last set of NOS 500 valves and guides and he's currently at the IJR in Poland so I've nothing to measure for you).

Good move to open up the inlet valve oiler screw; it can do no harm except maybe an oily plug and a bit of smoke, but since the zorst valve also seized it does suggest a clearance/lubrication issue on both valves. Either that, or there's the unlikely possibility that the guides have been inserted too far (the guide circlip should prevent this) and the wider ends of the valve stems just under the valve head are sticking/jamming in the ends of the guides but I can't see how that can happen.... :?
The only other remote possibility as that you have received the wrong valves and/or guides or that they have not been produced to the correct spec'n.

EDIT
Just another thought......do/did the valves free off when th'engine had cooled down? If not it might be that the valve springs, collets etc. have been fitted incorrectly preventing the valves from closing completely when hot....(Nah, surely not).
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Which taken at the flood............'
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1608
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Re: seizing valves

Post by 1608 »

Most of our air cooled bike engines have about a 4thou clearance for valve stems. Are the 'Engineering works' familiar with air cooled engine tolerances. If both valves have been seizing then they should be checked and if necessary reamed to suit. Where did the 'Engineering works' get their figures from.
Chris Berry
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Re: seizing valves

Post by Chris Berry »

Thanks again, this is all a great help. The new valves I put in are the same as the AMOC parts site now lists both valves under the same part no (for the 500) so I'm figuring if I get the engineer to set both guides to 0.004" I would have to be on the mark. Although the inlet valve did release under a little pressure the exhaust is quite set. I haven't tried any pressure myself as I thought I'd leave that to the engineer to save any arguments.
SPRIDDLER wrote:It's from the Army Workshop Handbook of Inspection Standards for the WD G3L from 1941 to 1953 which you will find in Christians Archives:

http://archives.jampot.dk/book/Workshop ... ndards.pdf

It's (probably the only) comprehensive and condensed information available in one document for tolerances and clearances apart from random figures that can be found buried in the multitude of Owners and Workshop manuals available, although I've never found valve/guide clearances anywhere else.
Whilst it's for a 350 and the 500 probably has larger dia. valve stems and guides I would suggest that the running clearances are a valid guide for your 500.......... e.g. similar materials, function and operating temps.
(I've just given a pal my last set of NOS 500 valves and guides and he's currently at the IJR in Poland so I've nothing to measure for you).

Good move to open up the inlet valve oiler screw; it can do no harm except maybe an oily plug and a bit of smoke, but since the zorst valve also seized it does suggest a clearance/lubrication issue on both valves. Either that, or there's the unlikely possibility that the guides have been inserted too far (the guide circlip should prevent this) and the wider ends of the valve stems just under the valve head are sticking/jamming in the ends of the guides but I can't see how that can happen.... :?
The only other remote possibility as that you have received the wrong valves and/or guides or that they have not been produced to the correct spec'n.

EDIT
Just another thought......do/did the valves free off when th'engine had cooled down? If not it might be that the valve springs, collets etc. have been fitted incorrectly preventing the valves from closing completely when hot....(Nah, surely not).
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Re: seizing valves

Post by SPRIDDLER »

I hope the zorst valve isn't stuck due to contact with the piston.
I've only fitted new valves and guides a few times and they've always worked straight from the box without any reaming.
I guess your engineer knows that the guides should only be removed and replaced after heating the cyl head at 180 deg F or Gas mark 5 for about 15 mins to avoid damaging the head. Pressing/drawing new guides into a cold head could also result in internal burring/distortion of the guide end, producing a tight spot.
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Rob Harknett
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Re: seizing valves

Post by Rob Harknett »

Neville has mentioned the possibility of valve damage being a cause of the valves sticking also given a link to a file on WD machine tolerances. These machines did have iron heads, I don't know if tolerances would differ with an alloy head. Neville also stated information of tolerances is not easy to come by. So I had a look. The company, Tranco valves, did produce some very informative catalogues. Any one got any copies they could loan me? Some detective work would still need to be done to discover tolerances. How ever, if you knew the valve stem dia. and the valve guide bore, would I be correct in thinking, the difference between the two, would be the tolerance? You will need to know the valve and matching guide for you bike. AMC & Tranco part numbers. Then go to the Tranco book where you see the Tranco pt. no. quoted that matches your AMC pt. number. Hope that all makes sense???? I have found some info that may help. 1. chart to see what AMC & Tranco pt. no. your valve and guide would be. 2 & 3, charts to see the Tranco valve and guide information. You can now find that here.
http://archives.jampot.dk/technical/Gen ... etails.pdf
If my theory is correct, that the Traco catalogue will help find valve and guide tolerances can be worked out. Check if you have a catalogue you could loan me. What I have found only covers some 250 and 350 AMC machines. I only have other manufactures cats. for pre war machines.
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Re: seizing valves

Post by SPRIDDLER »

Rob Harknett wrote: I have found some info that may help. 1. chart to see what AMC & Tranco pt. no. your valve and guide would be. 2 & 3, charts to see the Tranco valve and guide information.If my theory is correct, that the Traco catalogue will help find valve and guide tolerances can be worked out.
Yes........and no, Rob.
Using those charts (all for 350's) for the 1956/7 models it gives:

Inlet valve 4351 Stem o.d. 3/8"
Inlet guide 6436 i.d. 3/8"

Zorst valve 4352 Stem o.d. 3/8"
Zorst guide 6497 i.d. 3/8"

In other words, no clearances shown.

A couple of other years which I checked also show valves and guides as having the same dims. so as you rightly say, we'd need the exact Tranco tech spec's to work out clearances by deducting the valve stem o.d. from the guide i.d.
Shame.
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Which taken at the flood............'
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Rob Harknett
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Re: seizing valves

Post by Rob Harknett »

SPRIDDLER wrote:
Rob Harknett wrote: I have found some info that may help. 1. chart to see what AMC & Tranco pt. no. your valve and guide would be. 2 & 3, charts to see the Tranco valve and guide information.If my theory is correct, that the Traco catalogue will help find valve and guide tolerances can be worked out.
Yes........and no, Rob.
Using those charts (all for 350's) for the 1956/7 models it gives:

Inlet valve 4351 Stem o.d. 3/8"
Inlet guide 6436 i.d. 3/8"

Zorst valve 4352 Stem o.d. 3/8"
Zorst guide 6497 i.d. 3/8"
In other words, no clearances shown.
A couple of other years which I checked also show valves and guides as having the same dims. so as you rightly say, we'd need the exact Tranco tech spec's to work out clearances by deducting the valve stem o.d. from the guide i.d.
Shame.
I never checked anything Neville, that's very strange, stem dia and guide bore the same. Perhaps there is info in the cat. that explains, perhaps something like the I/S dia of guide bore stated, is the dia of the valve stem it accepts. So no need to worry about any clearance, just make sure you have the right bits and everything should fit OK. So there should be no problem fitting old or repro parts. Clearances all accounted for when parts are made. This does seem to suggest a bent valve. Try a known good valve in the guide, if that drops in Ok does the seizing valve also drop in OK
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