Spark plug re-thread and other issues

[1608]

Hi Paul, as usual you will get a jumble of suggestions and well meant advice to any problem on this forum, but! My advice would be to check the head for flat by placing on a known flat surface and check with a fine feeler gauge, and any rocking. Any well equipped garage or engineering shop will have flat bed that they would probably let you use just to check. Any high points you find might just be around to bolt holes. The head may just need a light flatting on emery sheet on a flat surface. I personally wouldn't recommend trying to grind the head and barrel faces with grinding paste as this is only adviseable when no head gasket is used. Use the paste for the valves only. Aneal a new copper gasket, re-tighten head in stages when cold and re-tighten after a run when cooled down again. re-check tappets.

[Janet]

Hi Paul, as usual you will get a jumble of suggestions and well meant advice to any problem on this forum, but! My advice would be..........

Well, that's just put us all in our places, hasn't it?

[Ozmadman]

He may have failed to anneal the gasket (even if a new one was used as Colin commented) or not tightened/re-tightened the head bolts sufficiently.

+

Just wondering, but if the engine had previously had a top end rebuild, is it one that needs the head tightening down again after a few miles and, if so, was it done?

I did notice a slight head gasket leak after owning it for a while so I purchased a torque wrench and discovered that the bolts were in fact quite loose cos I had to do them quite a bit to get to 35lbft. This stopped the leak but I suppose the damage was done?

The zorst port does look a bit cokey - was the inlet valve oil feed screw set correctly?

Yep 1/6th of a turn out from closed but I did mention that there was a lot of oil under the head gasket(it was obviously not sealing around the oil feed hole) and some on the piston so I was wondering whether the piston was sucking it down the bore on the inlet stroke but the bike doesn't smoke at all when running??? Also, how many times should the head be re-tightened?? Oh and the tappets, how much clearance if cold should I start with as I can't set them warm on a re-built cold engine..

Paul

[Janet]

Oh and the tappets, how much clearance if cold should I start with as I can't set them warm on a re-built cold engine..

My well meaning advice would be to set them so they rattle a bit. Better too wide than too tight. Hopefully it will fire up* and, if so, you can let it run until warm and then set them again so the don't rattle but will spin in your fingers.

*I've only just fixed one that has been too noisy since a couple of years but by then I'd got it starting and running well so kept leaving it for another day.

[SPRIDDLER]

I personally wouldn't recommend trying to grind the head and barrel faces with grinding paste as this is only adviseable when no head gasket is used.

Yep, I'd go with that. I was blindly following/explaining Rob's 'grinding in' suggestion, overlooking the gasket. Lightweight engines are not well known to me.

I did notice a slight head gasket leak and discovered that the bolts were in fact quite loose cos I had to do them quite a bit to get to 35lbft. This stopped the leak but I suppose the damage was done?

I certainly wouldn't use the old gasket again. It may have been faulty to start with. It happens.
Tighten down the head initially, then again after say 100 or 200 miles.
Make sure that compressed muck hasn't built up at the bottom of of the blind head bolt holes. If there is stuff at the bottom the torque wrench will click but the end of the bolts may be hard up against the muck and not pulling the head down as tightly as it should be. Same goes for the blind rocker cover bolt holes (if they exist on Lightweights ) - commonly a cause of leaks at the rocker cover/head interface.
Just a thought, but on the heavyweights there are specific thick washers under the head bolts. If the P.O. wasn't aware of this he may have fitted 'ordinary' washers which won't help the head being pulled right down.

[Ozmadman]

My well meaning advice would be to set them so they rattle a bit. Better too wide than too tight. Hopefully it will fire up and, if so, you can let it run until warm and then set them again so the don't rattle but will spin in your fingers

Thanks. will do then

I certainly wouldn't use the old gasket again. It may have been faulty to start with.Tighten down the head initially, then again after say 100 or 200 miles.Make sure that compressed muck hasn't built up at the bottom of of the blind head bolt holes. If there is stuff at the bottom the torque wrench will click but the end of the bolts may be hard up against the muck and not pulling the head down as tightly as it should be. Same goes for the blind rocker cover bolt holes (if they exist on Lightweights ) - commonly a cause of leaks at the rocker cover/head interface.
Just a thought, but on the heavyweights there are specific thick washers under the head bolts. If the P.O. wasn't aware of this he may have fitted 'ordinary' washers which won't help the head being pulled right down.

Thanks, will use a new gasket, has anyone got any experience with ally gaskets? (I do have a rare copper new one as well though). Will also check out the blind holes and yes there are thick washers on the head bolts but why not make the studs a bit shorter (even an 1/8" would have done it) to give more useful thread in the head bolts? why did they design it like that to the effect that the thickness of a washer could prevent the head from being fully tightened down. Think even my 11 year old could have worked that one out.

Paul

[SPRIDDLER]

The precaution of cleaning out blind holes, using the correct washer etc. is more a question of good practice and eliminates the possibility of an accumulation of two or more elements combining to cause a problem. Each on its own wouldn't necessarily cause a problem.
As far as making the bolts shorter or the threaded hole in the head deeper I think it's the case that the teams of draughtsmen/women didn't anticipate or weren't familiar with the bodgings of Saturday mechanics but designed components somewhat academically in their wing collar, slide rule and pipesmoking environment.
And by the time the production engineers, cost accountants, and the purchasing department had their input the finished items were frequently very different from the designer's aspirations.
There are many examples of the designer's frustration in Bert Hopwood's book 'Whatever happened to the British motorcycle industry'.

[Ozmadman]

Thanks Neville, will take all that on board when I come to put it all back. Has no-one used an aluminium head gasket on a lightweight before? I have one and am wondering whether to try it??

Paul

[Ozmadman]

Well, spark plug thread fixed and done by myself with a decent kit which cost me £48 but well worth it!! Actually it was dead simple, just need to be a bit brave rethreading the hole. I did a lot of research and decided a solid insert would be better that a wire, helicoil type one. I avoided the cheap ebay offerings and went for one made by Volkel.

Check video here http://www.voelkel.com/en/service-en/te ... os-en.html

I contacted the company and asked about the security of the inserts and was told they "should" remain in place when you remove then plug. Me being me I used a small amount of some loctite retaining gunk I had on the insert and copper slip on the plug and all seems well so far, must make sure though I only remove plug when cold.

[Ozmadman]

and "flatted head" and new inlet valve (wasn't happy with the old one) just need to grind in the valves now

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