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[Cranky]

Its a whirring noise and a clanging noise. The piston slop totally unacceptable and is a good candidate for the clanging.

I started to re build and then I noticed the Timing side crank bearing was infact --not perfect I had .025mm play.

I drove over 150km yesterday looking for a piston in many many shops and engineers. The language was a barrier but I struggled through. I came home without a bearing or a piston.

The bearing is ordered from the bearing factors near buy . I have managed to find a piston from a Honda generator at 88mm with a 20mm pin and 20mm compression distance, this was just under 8 quid with rings, pin and clips.

The piston is 88mm so Im not sure wether to skim that on a lathe or make a new liner or both.

Any one clever enough to work out the new capacity of a 88mm. It looks from the picture to have a dish as is the same but with 4 little notches for the 4 valves. Pretty cheap at 8 quid and worth it just to look at it. I spent quarter of a tank of Deisel yesterday for nothing,--that was 10 quid.

[vince]

Hi , 547cc. Vince

[Cranky]

Hi , 547cc. Vince

547cc Hmm that sounds good. Ok here is the interesting bit. A 88mm piston will require the removal of 2mm each side of the liner. Now the liners sticks out a long way all on its own, looks a bit odd too. Im wondering if a 2mm liner sticking out that far all unsupported like will be ok.

On the internet is information suggesting that turning a piston is not advisable but this is for a 6:1 compression ration Royal Enfeild not a Dragster. They talks of barrel shape on purpose and the piston expansion to bring it to a round shape for perfect performance, again this is not a high performance engine.

I am therefore toying with the idea of turning the piston down to 84. This will obviously need ring groove deepening but I dont see that a round straight piston will be a disaster.

Any thoughts anyone.

[vince]

Hi, thats a lot to take off the piston unless the skirts are very thick to begin with.

[Cranky]

Hi, thats a lot to take off the piston unless the skirts are very thick to begin with.

Yes that is true, maybe a bit of both. Its on order, when it comes ille consider my options --in the meantime time engine is back in with a new Timing side Japanese bearing and what a difference. The jap bearing was much tighter fit of the inner race and much tighter fit of the outer race. So much so I can tell the different fitting of the cam gears. When fitting the crank it did not just slop into its hole but needed to turn to wind its into way down into the bearing.

Jap V Czechoslovakia.


Oh by the way I investigated the liner to crank case fit. It is not a fit but a slop. I did'nt measure it but its about 5 thou.

This could be the clang clang imitating piston slap. The liner is slapping the crank case. All go to be considered.

[Rattlebattle]

Interesting comment re bearing. I had thought that the replacement I bought from our host would be superior to the original. In fact it’s the same and just as sloppy, so I assumed it was normal. Looks like maybe I just need to replace it again with a decent Japanese one then, as the crank did pass muster. All that blo*dy work too...

[Wheaters]

When it comes to bearings, there are different specifications for clearance between the moving parts. Is the bearing in question by any chance a C3? These are designed to have a relatively loose fit.

[Haggis]

The two left hand bearings have different clearance values, different types of bearing though.
No details for the right hand bearing.

[Rattlebattle]

IIRC the t/s bearing is a C3, which I understand is a “sloppy” fit. I have to say that there was no discernible axial play on the crank with either the original or the replacement bearing. Is the machining sufficiently accurate for a tight bearing I wonder? Maybe that’s why the Carberry was designed, to tighten it up?

[Wheaters]

There we are. It’s a C3, which is designed to have a loose fit.

A C4, also listed there, has even more clearance.