Piston Side Play Issue

Woollybandit

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Stripping down a 'new' '72 Bonnie due to smoking exhausts with it in my mind it’s oil either passing down/around the guides or down the head studs and across the gasket.

Firstly, two of the inner stud holes in the barrel are saturated with oil which tells me I need to seal around the head bolts on reassembly.

Secondly when I rub the piston tops to see what oversize they are (+020 it turns out) the pistons move fore and aft more than I would expect. To be precise I think they are rocking on the gudgeon pin so the question is that there must be quite a skirt clearance at the other end!
About halfway down the stroke the piston side clearance down to top ring is about 15 thou all round using a feeler gauge.

Later today I will pull the barrels and pistons to see what state they are in. What I can see of the bores seems clean enough with minor wear scrapes.
It almost looks like a rehone and new pistons and rings will suffice as I don’t want to use up all my rebore lives unnecessarily and the wait for a rebore is several weeks.

Any comments on my thoughts and the piston rocking would be appreciated. Rediculous as it sounds it seems like the pistons are a size too small for the bore!!! Certainly oil is in the chamber so could be going up from below in addition to above. Piston tops are uniformly black all over.

Thanks
 

sikatri

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Post pictures when you pull them.
 

grandpaul

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They've got to be measured (bore, pistons, and ring end gaps), then compared to spec. You will get noticeable play but it's down to proper allowance.
 

Woollybandit

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Photos of parts
C3FEE0AB-F15E-4D2E-B635-08B6A102905B.jpeg6FA8BE05-DF77-4CC1-8241-DE7D8C0768CB.jpegE1D47188-206B-4C9A-A5EB-50DE36539E6B.jpeg3399BA44-71A8-4AB1-8D7D-6AD88AA26FD0.jpeg79F24B95-D367-4E75-807E-3F4E1EEA8427.jpeg3878D4C3-8A73-46D6-9D9A-396C8F154CBA.jpeg1E82FFD1-4211-46D7-A282-700F04CEC0E6.jpeg
Took to workshop specialists in Triumphs and Brit bikes this afternoon. They measured and despite looks the pistons and barrels are within specs for +020 …….. probably at oppos ends of the limits but ok.
I bought on their recommendation an oversize set of new rings and a few gaskets with strict advice to check ring end gaps! Old ring end gap halfway down bore was about 25 thou, by eye

Nice set of rods!!!
 

Woollybandit

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Just as an aside, when I examined the barrel one of the inner stud holes on each cylinder had stinking oil in the bottom. Obviously from the rocker boxes (where else?) so on reassembly I will pay particular care sealing those four studs.
 

grandpaul

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I was going to say, those pistons and bores look MUCH better than most used stuff I've had my hands on.

Then again, most of the stuff I've had my hands on looked kinda like this...

0406-01.jpg
 
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