G80CS... and the saga continues

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Re: G80CS... and the saga continues

Postby clanger9 » Fri Sep 21, 2018 6:52 am

Definitely check the head for flatness. It looks like the head gasket has been leaking in the area between the pushrods.
Get a new set of valves as well, as you mentioned the exhaust isn't straight. Then check the clearance on the guides. You'll may find they're OK with new valves.

I don't think your valve seats will recover with a re-grind, so get the seats re-cut by an engineering shop. They can also check the guide clearance and replace them if necessary. This will ensure the seats are exactly concentric with the guides.
I would go with the clearances from the manual. It gets hot in Australia and you might find the guides nip up at lower clearances.

Oil can't "come out of the plug hole", as the plug provides a tight seal. The oil there is collecting from a leak above. Just check the rocker box face for flatness (lap it on a sheet of fine wet & dry on a sheet of glass) and use Wellseal on the gasket and it should be OK...
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: G80CS... and the saga continues

Postby Mick D » Fri Sep 21, 2018 8:11 am

Hi

In my opinion if you are going to the trouble and expense of replacing the valves and re-cutting the seats it would be false economy not to replace the guides at the same time.

Regards Mick

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Re: G80CS... and the saga continues

Postby Mick D » Fri Sep 21, 2018 10:34 am

Hi

The oil leaking down the rocker box to the plug area looks like it could be coming from the valve lift spindle seal.

Regards Mick

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Re: G80CS... and the saga continues

Postby ajscomboman » Fri Sep 21, 2018 10:38 am

Mick D wrote:Hi

In my opinion if you are going to the trouble and expense of replacing the valves and re-cutting the seats it would be false economy not to replace the guides at the same time.

Regards Mick


Couldn't agree more, looking at the head it's not surprising that Marty has had so much trouble. Guides, valves and a seat recut is the only way to go. Lap the head and barrel together and then use the head gasket once it's been annealed. Rebore and a new piston along with the correct carb settings and the job should be a good un. I'd also have a real close look at the rocker box as I agree with Clanger, no way is that oil coming from the plug area (well shouldn't) and if it is then that's another reason for no compression. I'd lay money on more hairline cracks or decompressor o-ring or possibly a warpage, that is unusual but not unheard of. Either way it needs addressed. As for running clearance in the guides, if your lucky they'll be a nice fit without having to ream out. If you do have to ream I'll recommend you go with the manual, can't have any blame then (I'm a coward!).

I'd say we're making progress, if at the expense of making Marty a little poorer!

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Re: G80CS... and the saga continues

Postby Matchymarty » Sat Sep 22, 2018 8:17 am

Hmm.. Ok folks.
Update.
I have pulled the valves out and measured them. Does anyone have measurements of new valves for a 500 / 500CS?

I have compared with father in laws spares, and mine seem bigger!

EXH - 'V56' Marking only. 4.0365" long. 0.3725" Thick Stem. 1.6855" diam head.
INL - 'INLV' marking only. 3.9665 long. 0.372" Thick Stem. 1.6905" diam head.

Does this sound right?

I have two 'OK' valves I can use from Father in law.
EXH? - 'V57 KE' Marking. 4.0585" long. 0.3725" Thick Stem. 1.593" diam head.
INL - 'INLVL' Marking. 4.3185" long. 0.3735" Thick Stem. 1.591" diam head.

I also can buy a pair of
'Part# 013988, V55' and Part# '013989, V56' valves and guides locally.

I'm at a loss here, but my book says 013988 and 013989 are for 'ALL 500cc' Engines ?! is this correct?

This is critical I get the right valves, and QUICK. I have to have my Matchy back up and run in in 5 weeks for the annual National Jampot Rally!

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Re: G80CS... and the saga continues

Postby ajscomboman » Sat Sep 22, 2018 10:35 am

I'm at a loss here, but my book says 013988 and 013989 are for 'ALL 500cc' Engines ?! is this correct?


As far as I can research, right up to 1959 for the longstroke motors those numbers are correct.

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Re: G80CS... and the saga continues

Postby Matchymarty » Sat Sep 22, 2018 10:05 pm

Thanks AJSComboman.

I did some more searching through the Forum and found a link to GS VALVES in UK. They actually had specs for the V55 and V56 valves and are meant to be as follows :
1.690" head diam, 0.373" Stem, 4.060" Length.

So it looks like I have an inlet valve stem that is 0.0935" to short (2.4mm). The collet rings are in the same position on the stem from the valve seat head as the other valve, I just wonder if the valve is opening enough. I realise pushrod adjustment would take up the difference, but there is evidence of hammering on the stem end, and so I wonder if the rocker is topping out before it's opening fully ie, getting full lift from the cam.

At any rate, I'll get the right length ones and hope for the best.

Cheers.

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Re: G80CS... and the saga continues

Postby Expat » Sun Sep 23, 2018 12:57 am

Sounds like a good plan Marty. :)
Keep shiny side up.

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Re: G80CS... and the saga continues

Postby dave16mct » Sun Sep 23, 2018 6:17 am

That shorter valve may have been from an earlier model which had hardened caps on top.
Dave.

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Re: G80CS... and the saga continues

Postby Braaap » Tue Sep 25, 2018 7:10 pm

Hi. I would question the timing.
My G3L was running way too much advance. Somehow i had made a complete hash of timing it.

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