G9 Cylinder Heads

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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john kitchen
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G9 Cylinder Heads

Post by john kitchen »

I am soon to be re-fitting the cylinder heads to my G9. Any pointers would be appreciated as I understand the studs can be snapped?

I would also like to know which way up do the oil metering jets go into the heads?

Thanks

John.[8D][xx(][xx(]
Eric
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G9 Cylinder Heads

Post by Eric »

Its true if you overdo things the studs can shear, they are only 5/16" diameter. Some have opened things up to 3/8" as used on later engines but this should not really be considered essential. If you have no idea of how many times the heads have been off and on new studs are recommended. I bought mine from the club spares, but they were the wrong length, so I then got some stainless steel ones made up by Acme Stainless the details I have given you before (I think). The 1960 G9 engine uses different lengths to earlier engines. The manual I mentioned before does have some torque values somewhere, if I can find them I will let you know. As for the metering jets where are they located? Do you mean the ones in the rocker spindle housing of the heads?

john kitchen
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G9 Cylinder Heads

Post by john kitchen »

Eric

The oil metering jets go into the oil way just above the head gasket but they can go in either way around?

I have the torque settings from the technical section of the web page.
What I am wondering is are they tightened down fully or partially tightened and then finally tightened after the engine has been to ran?

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silverarrow
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G9 Cylinder Heads

Post by silverarrow »

John,

A pal of mine has made the change to bigger dia studs on his 55 G9 and means an extra 5lb/ft can be applied and means extra security of the head gaskets as well. A good mating surface on head &block should mean the statdard studs will be OK but do not be tempted to over torque the nuts down as if they do not ping right away may wel do once operating tempertures are reached.

|In general torquing down heads i would take two and preferably 3 stages in clamping down. so say the finished torque is 30 go to 20 first then 25 and finish on 30. I would also take the bike for a good run to ensure full operating temperatures are reached then slacken off the head and re torque as before when the engine is again cold. Do it all again after 250-500 miles and it should trouble free. I confess to only having singles post war but what is a twin other than two singles.

Les Smith (silverarrow397) [:o)]
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Eric
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G9 Cylinder Heads

Post by Eric »

John
My memory no longer includes reference to the oil metering plugs, so I looked in the book. If I am correct they are part no 018890, the book suggests they were omitted for 1959 models, so your 1960 should not have any. Maybe that’s why I don’t remember them. They were apparently put back again for 1961 models. To remove them (If fitted) the book says: - Apply gentle heat to the cylinder head and push the plug through the drilling to come out of the hole in the rocker post. To fit new ones insert small end inwards, a light tap with a centre punch in the larger hole will retain the plug in position. I assume this is all done from the head face upward. Only you will know if there is a small end and a large hole, as I guess you have some new plugs to fit. I don’t know what torque figures you have seen but beware those given by Les; the book has 16 ft lb for 5/16 dia and 25 ft lb for 3/8 dia. I don’t have a torque wrench but I know you tighten down diagonally (Fit the inlet manifold loose on studs first) as required. After running the engine the first time for a few minutes, allow to cool and tighten again as before but don’t undo them first. Then do them at least twice more during the next 500 miles. I then nip mine up every winter before checking the valve clearances. Hope this helps.


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silverarrow
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G9 Cylinder Heads

Post by silverarrow »

Eric is quite correct the torque figures i used were rfor purposes of explanation of principle only. I was probably thinking about silver arrow cast iron heads with those numbers. Still best to take up in stages whatever the end figure you are aiming at. As my torque wrench starts at 15 lbs light manual nipping up is often needed before use.

Les Smith (silverarrow397) [:o)]
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lawrence
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G9 Cylinder Heads

Post by lawrence »

Eric
A torque wrench is a good investment. They can be purchased really cheaply nowadays (£15ish) and you would be surprised how inaccurate 'feel' is on bolts. Having said that, the only time I have recently stripped thraeds was setting the dome oil feed nuts on my Bonnie using a TW. I told the chap I puchased the replacements nuts from and he said "The Triumph manual settings are wrong, I thought everyone knew that by now" D'oh!

Lawrence[}:)]
Eric
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G9 Cylinder Heads

Post by Eric »

Lawrence
You maybe right, perhaps I should consider investing in a TW. I know that I once thought the purchase of an impact screwdriver would be resorting to the use of brutality to reomove stubborn fastners, but have since discovered just what a brilliant tool they can be. Incidentaly RIDE magazine have just tested TW's, they dont think much of the lower priced ones but have given Best Buy status to the Halfords Professional 3/8 drive one that is a re-branded version of the equivalent Sykes Pickavant one but £49.99 instead of £67.60 for the SP. I can also recommend the Halfords digital tyre pressure gauges the long neck one with the business end at 90 degree angle being the best its about £9.50 and measures in 1/2 psi. Or things called Bar if you want them.

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silverarrow
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G9 Cylinder Heads

Post by silverarrow »

I to used not a TW for many years but now find it an essential tool. I believe when tighening a head or an alloy cover for example even tighening is of greater importance than the pressure although clearly not enough or too much of the latter is unexceptable.

A cheap TW i would think is better than none as if it only a few lbs out and is consistant that's not to bad.

Might take a trip to halfords though. I fancy a digital tyre guage if it proves half as usful as my digital micrometer. my tyre guage is doubtless older than my Ajay!

Les Smith (silverarrow397) [:o)]
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lawrence
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G9 Cylinder Heads

Post by lawrence »

There are some amazing tools available now. you can buy a digital chain adjustment guage for about £40. I'm sticking to my ancient tape measure till they come down to 99p![:0]

Lawrence[}:)]
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