G80s valve oiling and head bolts

[56G80S]

I took the rocker box off the Matchless to re-torque the head, which had done 350 miles since new valves and guides and a skim following blown head gasket.
Surprised to see that the drive side rear head bolt was completely dry, whereas the other three were covered in oil as one would expect. Inlet valve collets still showed the high melting point graphite grease I had used to hold them in place during re-assembly. I'd removed the inlet oil needle valve and made sure all oilways were clear after fitting the new guide.

But there are no scratches /marks on the exposed part of the valve stem (used magnifying glass). Very slight scuffing on the valve end (none at all on new exhaust valve).

When I put the piston at TDC before starting work, the tappets were a tad slack as one would expect from a completely cold engine, but nothing out of the way.

Any suggestions?

On a related tack, the pillar that the “exhaust” head bolt goes through is cracked in a couple of places and was easier to back off than the others, all were torque to 35 lbs ft. Marked them all before backing off and re-torquing to 37 lbs ft; the other three all exceeded their initial mark by the same amount, while the “exhaust” one doubled their score.

Guess I'll pack a spare gasket for the IJR.

Three of the rocker box bolts had less gap under their heads when undone and resting at the top of the head threads. The two “head steady” bolts and the middle one above the tappet cover only had 0.7cms; all the rest had 1.3cms. Funny I'd never noticed before.

Oh for the heady days of disregarding all this stuff, when maintenance was putting in oil when one remembered and sometimes inflating the tyres!
Johnny B

[MatthewC]

Scuffing on the inlet valve stem on my G3 seems to be associated with no air filter; using one keeps the stem looking like new. Oil flow in the head seems to be just enough and no more, I've often found dry areas and have concluded that it's not worth worrying about as the bike seems unaffected and the moving parts have always had oil on them in the right places.

On the subject of head bolt torque, using 35lb.ft I had endless trouble; it distorts the gasket surface, damages the pillars under the bolts, damages the head gasket and the head bolts appear to slacken off - in fact it's not the bolts loosening but the head compressing. With some experimentation, I've found 25lb.ft to work well (starting with a fresh gasket as one previously used at 35lb.ft will have differences in thickness of several thou); retorqued once after 100 miles the only bolt that goes any further is the one nearest the exhaust and that only slightly. Then ignored until the next decoke is due. And the bike gets worked hard too, it's quite happy to sit at 60+ for as long as the rider can tolerate it with bursts up to 70 or more. I've had to slow down a bit though as the tinware has suffered, I've now got a few splits I need to weld.

Regarding the differences in height of the rocker box bolts, I can't think whether mine are like it but I'd be inclined to check that the threads in the head haven't lost a few turns. They're only 5/16 BSF and seem to suffer over the years in the hands of less sympathetic previous owners.

I hope you find something useful in the above.

Matthew

[56G80S]

Matthew

Thanks for the very interesting and illuminating response, particularly regarding the oil matters.

Unfortunately, I am that hamfisted previous owner, as I've had it since I was 21. I've learnt since and was only going for the 35ish torque in the light of other threads on the forum. Worst thing I did was overtighten the nut on the exhaust cam, snapping of the "stud" on an SH camwheel, but that was when I was 22 and knew less than now (at 60).

Your statement about the reduced thickness of heavily torqued head gaskets is borne out by my measurements of "old" re-used gaskets.

I now realise that the rocker box bolts that are "short of thread" are ones I helicoiled (vcoiled actually) and I may've wound the insert a tad further in than necessary, but should be OK there. I've also relieved the edge of the holes. Ironically, having just taken the rocker box off, it was lovely and oiltight

Rest assured, I no longer snap off bolts (or screws in woodwork) like I used to!

Thanks again

Johnny B

[MatthewC]

Johnny,

I'm glad it was of use.

To expand a bit on the torque figure, I too read about head gasket troubles on the forums and followed the concensus by torquing the head bolts to 35lb.ft, then retorquing after 100, 500 and then 1000 miles. Incidentally, that torque figure is one of two which are given in the factory manual (and not where you'd expect to find them either!) A year and a half ago I bought a good second hand head; you know the imprint they normally get from the gasket, well this one only had the very faintest trace of that. The next time I had the head off I noticed that it was quite distinct, and if you look closely you'll see it's deeper nearer the bolts. The same goes for where the washers under the bolt heads press into the head, this head only had a minimal amount of that until after I'd used it, when it was worse. These two problems (combined with the head gasket leak yet again) are what made me realise that the factory torque figure is too tight, leading to some experimentation before I settled on 25lb.ft. It just goes to show that following instructions doesn't always work!

Incidentally, I've noticed when looking at autojumble heads that the earlier alloy heads are almost always in better condition than the later ones, it makes me wonder whether the quality of the alloy used went down? I also wonder whether the factory put the figure in the manual because they thought they ought to, but just tightened things by feel when they actually built the bikes?

It might sound perverse, but I'm glad I bought a much abused bike; it may have been very trying at times but I enjoy working on it almost as much as riding it. There's plenty more left to do to it, so it'lll keep me busy for a while yet. Joining the club and these forums was one of my best moves, they've been invaluable.

I wish you good spannering and good riding,

Matthew