Bsa c15 ss80 help

[Last stand]

Hello all I am a new member to bsa owners club. So I have recently purchased my first 1964 bsa c15 ss80. After around 3 weeks of ownership I noticed the bike started smoking blue. Cut a long story short who ever did the rebuilt previously had not seated the clip correctly on the piston and it then decided to wipe my barrel out! It's to deep to carry out a reborn as it was already on +40. Sorry I'm very new to this so forgive me if I get things wrong. So I have recently purchased a re bored barrel (69mm with 9-1 hi comp piston) so after putting this back together loosly we noticed the piston is fouling on the cylinder head slightly and likely the valves... (my understanding is the ss80 has the bigger inlet valves likely casusing a problem) my question is can I shave some off the top of the piston or does anyone know a piston that I can fit without any issue. I'm having trouble finding any ss80 pistons which I believe needs to be +60.. or does anyone have a ss80 barrel and piston for sale. Many thanks in advance Chris

[cdsdorset]

Kidderminster motorcycles are listing a +60 ss80 pisto.

[Last stand]

Strangely enough iv just been In contact with them. So I'm learning more about the bike as each day goes on. So the barrel iv purchased is newly bored 69mm with a triumph 500cc hepolite hi comp piston in. This piston doesn't suit the ss80 and is what's fouling on the cylinder head /valves etc..  I need a normal comp piston that isn't to domed shaped at the top. Any ideas which piston would suit.

Thanks again

[Spaceman]

I had the same thing happen with the first bike I owned - I definitely learned a harsh lesson of the need to use new circlips each time you replace a piston rather than re-using the old ones. One circlip popped out and resulted in the dungeon pin gouging a 3 mm groove down one side of the barrel!!

Consulting the Bible (Rupert Ratio Vol. 1), it looks as though Trident/Rocket 3 pistons will fit which come in a range of compression ratios and some look to be available in +80 thou or 2 mm oversize. As RR says, it's a question of looking to see what you can get your hands on as far as the C15 is concerned. For example, there is a cheap +40 thou oversize SS80 piston being advertised but you would then have to find another barrel to take it.

[cdsdorset]

Have a chat with Cox and turner in Verwood.

[Rupert]

Triumph 5TA std piston is +.080" in a C15, works well. New Hepolite copy pistons by Wassell seem ok. Don't fit daytona piston as comp Ratio is too high.
Otherwise Westwood cylinder liners do a liner to take it back to std.

[Last stand]

Thankyou all for your replys. So still deciding what to do with regards to the the triumph hepolite 500 piston 9-1 comp iv purchased with 69mm bored out barrel. Because the barrel and piston is obviously Oversized it's causing the outer of the piston to foul on the cylinder head.. it needs to be de coked which will allow some room but would putting 2 of the copper head gaskets on be wise? To help with clearance? Any suggestions welcome. I purchased the barrel/piston off ebay which indicated a direct fit without mods. Maybe because mine is the ss80 rather than a standard c15 this is why I'm having issues with piston/head.

Thanks chris

[Spaceman]

It would be worth measuring the height of the outer edge of the piston crown above the gudgeon pin for both the old piston and the new one to see how they compare. That would at least tell you the size of any clearance issue as regards to the edge of the piston? However, I would have thought there is a high likelihood that it is not just the edge of the 9:1 piston that is fouling.

[JulianS]

There are 2 different design 69mm bore Triumph 500 9:1 pistons. I recall that they do not interchange

First for 1958 to 1967 season models.

Second from 1968 - this piston has a significantly higher compression height to go with a  combustion chamber which has a larger volume.

Which piston do you have?

Just having the right right bore piston is not enough - it needs the other dimensions - the compression height, the length and the size of the valve cutouts in the crown to be compatible with the geometry of your C15 engine.

[Last stand]

Hi again thanks for your replys. So here is a copy of the advert from eBay in which I purchased the barrel/piston. BSA C15 BARREL FRESHLY REBORED AND  HONED TO 69MM DIA WITH CORRECT .004  THOU CLEARANCE BETWEEN PISTON AND CYLINDER WALL COMPLETE WITH NOS AE HEPOLITE TRIUMPH 500 HIGH COMPRESSION PISTON 9-1 CR RINGS GUDGION PIN AND CIRCLIPS MAKES IT 280CC , FITS STRAIGHT IN NO MODS NEEDED.

Currently the bike is in my uncles garage so he can work some magic so I can't tell you what the exact piston is.

Iv attached some pictures from the advert.

P.s would it be OK to shave a little off the new piston to match the original piston I had in?

Thanks
Chris

[Spaceman]

If you compare pics of this piston against a pukka SS80 piston, the flat top on the latter looks to be twice the width as the Triumph piston which probably means the Triumph piston crown is a lot taller. As well as measuring the height of the piston skirt (relative to gudgeon pin) for the 2 pistons you have, it might also be useful to measure the relative crown heights. At face value, it looks as though you might need to shave off quite a bit off the Triumph piston crown to match that of the SS80?

[Last stand]

Hi yes I will compare the difference, the Bsa piston that came out was +40. Unfortunately the damage on the barrel was to bad to go out to +60 hence why I went for the alternative on ebay. Certainly the dome will need some shaving off. Would it be OK if I used 2 copper head gaskets for more clearance? Or is this not recommended. Regards Chris

[DAVE BRADY]

Hi,

Before shaving anything off the piston check to see how thick it is.  The high dome is pretty much hollow if you look at the inside.  Remove too much and the top of the piston will cave in during use.
Two gaskets would reduce the compression but could make things like push rod lengths and rocker angles less than ideal.

Dave.

[Last stand]

Hi Dave thanks for that. I'll look into it over the weekend with my uncle and decide what the best option is. Ideally would have been nice to have got a barrel/piston that would suit my ss80 but doesn't seem to be much about at the moment. I'm sure we've got a few routes we can go down

Thanks Chris

[Spaceman]

I would recommend measuring up the piston and combustion chamber to work out whether this Triumph piston stands any chance of being suitable. The sketch shows some critical dimensions.

Apart from the depth of the combustion chamber (H) and the height of the piston crown (h), the other critical dimension is the height of the piston skirt at TDC relative to the bottom of the combustion chamber (dimension 'c'). At the moment this dimension is probably negative but it would be interesting to know what it is with and without the head gasket in place. This dimension will tell you whether using 2 x head gaskets is likely to help.

One of the other critical dimensions will be H - h + c - the clearance at TDC between the top of the piston crown and the top of the combustion chamber. This will show how much might need to be skimmed off the top of the crown to provide enough clearance.

Unfortunately, even if you can make these dimension works, there would still be the clearance needed for the valves to be considered. In principle, this could be checked but you would probably have to generate an accurate engineering drawing to do this.