Shake, rattle and roll.

Ib-Denmark · Post by **Ib-Denmark** » Wed Jun 04, 2003 7:40 am

Hello,
This winter I bought a new piston for my G80S 1957 at the club spares scheme. The piston is + 60.
After honing the barrel to a clearence at 0.10mm (0.004 inch) it was assembled. But I have a very sharp, metallic rattle which sounds to come from the barrel? The sound is only at low revolutions. Not much difference at cold or hot engine. After 600 miles I opened the engine, but everything seems to be fine. The engine is still rattling!
Any ideas? Is this common? Could it be something else? Ignition fault perhaps?

Regards
Ib Vestergaard, Denmark

silverarrow · Post by **silverarrow** » Wed Jun 04, 2003 2:31 pm

A 'mettallic' rattle sounds as if it may be camshft end float. The camshaft should be shimmed to avoid this. did you disassemble this part?

Les Smith

Ib-Denmark · Post by **Ib-Denmark** » Wed Jun 04, 2003 4:48 pm

Hi Les
Timing side was not disassembled this winter, and the sound started after exchanging the piston this winter, but of course I will now go to my cellar to check the camshafts immediately.
Regards Ib

Adrian Pancaldi · Post by **Adrian Pancaldi** » Wed Jun 04, 2003 11:38 pm

Hi, did you measure the piston to bore clearance with a ringless piston in situ? Your clearance doesn't seem excessive but the problem sounds like piston slap.
regards
Adrian

clive · Post by **clive** » Wed Jun 04, 2003 11:50 pm

I have had a problem with the skirt not having sufficient cutaway to clear the flywheels on bottom dead centre. Not a club piston though and this was on 49 flywheels which I believe are a bit larger than the rest. Sorted my problem out by increasing the skirt using a bastard wood file so the teeth did not clog up with the alloy. Real engineers are probably now having to call the ambulance after the heart attack. Worked for me though.
The syptom was a mettalic knocking by the way but I would have expected something to show after 600 miles, maybe even to have broken by then if it was the skirt touching.

Jackson · Post by **Jackson** » Sun Jun 08, 2003 11:01 pm

Hi,
I have also fitted a +60 puiston (GPM Italian) to my 1955G80S and have a similar(?) sound. Unfortunately I had not run the engine before the rebuild so do not know what it sounded like.
If the only change you made was the piston, if could be that, but maybe a result of improved combustion/performance somewhere else?
I stripped my engine down after 1000 miles to invesigate having read Fred Neill's excellent book AJS single cylinder. It goes into so much detail on noises you will wish you had not read it!
I could find nothing terribly wrong except the cam followers/guides were a bit slack so I replaced them.
I had suspected the small end, but it was fine.
I still had the same noises after the rebuild!
I'm convinced now that at low speed it is the mechanical crank shock absorber working and at other speeds it is backlash in the timing gears.
I am just getting on with riding now, perhaps I will investigate again next winter!
Let me know if you resolve it!

alpraphoto · Post by **alpraphoto** » Tue Jun 17, 2003 2:31 pm

Hi Ib
I don't know if it's relevant, but I recently put a new piston and rings in my enfield bullet 350; the barrel was worn, but the existing piston was already max oversize, and I didn't want to get a new barrel. It immediately improved the weak compression, but also rattled in a dreadful tinny way that sounds similar to yours. I opened it up again and found the ring gap had increased from when I'd reassembled it, don't know why. Anyway, I've now 'bit the bullet' (pun intended) and got a new piston and barrel and it's fine.

Ib-Denmark · Post by **Ib-Denmark** » Tue Jun 17, 2003 9:19 pm

Hi everybody

Thank you very much for your advice.
I have now tryed everything. (exept exchanging piston and barrel)
----Still the same!!-
Do I really have to live with it?

Regards
Ib

Ib-Denmark · Post by **Ib-Denmark** » Sat Jun 21, 2003 4:54 pm

No more rattling, still I am a bit shaken and my eyes are rolling.
After having opened and reassembled the engine 3 times in two weeks I gave up: Now I have exchanged the piston.
The rattling piston was an Italian GPM and the new one is a (used) Australian JP with new piston rings.
I don´t know anything about piston design, so I will not judge the one piston mark to be better than the other. I can only say that this really did it!
To be honest I must say that the rattling has not completely dissapeared, but the level is very low and after reading several books which says that some piston slap is OK I can now sleep at nigth again.

Hope to see you all at the International here in Denmark next year!
Ib

silverarrow · Post by **silverarrow** » Tue Jun 24, 2003 11:29 am

So pleased you have sorted it. did you notice any difference in the weight of the two pistons. I have heard that some replacements are quite a bit overweight and enough to throw out balance factors and cause vibration. Les smith