BSA L29

[robbsa]

Good news, I have obtained a split washer, connected up the spark plug and attached the magneto to my drill......and have a spark!

Thanks for the help.

I've built myself a jig to help me work on the engine whilst I work on the frame. and the next step is to get the piston and cylinder head back on. The bore looks okay in the cylinder but since been left in the garage, the piston has got a bit of surface corrosion and also has some carbon build up.

The surface corrosion looks like it could be taken off with a bit of emery paper, but I'm guessing this will possibly ruin my compression?should this be machined? not sure how to get the carbon crust off without damaging the piston. Any further top tips?!

[R]

Yes you have to be cautious using emery cloth ANYWHERE inside an engine or on components,
the particles can remain, and turn into grinding paste !

The corrosion on the side of the piston if machined off would cause the piston
to have more clearance and thus piston slap - but won't affect compression.
I use a well blunted stainless steel wool - give all your saucepans a good clean with it first,
to blunt all the sharp edges. Polish in small circles, so you don't wear grooves in any particular direction.
Watch that it doesn't produce any visible scratches, in which case its not blunt enough.

The carbon on the top of the piston can mostly be scraped off using a blunt instrument - I mostly use a
sharpened wooden stick !  The aforementioned stainless steel wool also works well here.
Again watch that there are no scratches -  the piston top is not really a working surface,
although the finish is often less than pristine from previous owners attempts !
Smoothing off any previous scratches is a good plan, you don't want lumps or bumps becoming hot spots,
and possibly causing pre-ignition.


And the reason I mention STAINLESS steel wool is that ordinary stuff leaves tiny bits of steel wool everywhere,
which soon rust if exposed to dampness anytime - the last thing you want inside engines. (or outside for that matter).
Stainless wool  mostly breaks into long strands, which are easy to spot - and obviously kept away from inside engines.
have fun !

[R]

P.S. I should have first asked if that piston is iron or alloy ? It looks iron ?
Iron can withstand stronger treatment, including fine filing.
And is less prone to emery particles embedding in the surface.

[cardan]

Alloy I think, judging by the look of the corrosion. I use a stone lubricated with kerosene (paraffin I think you call it) on cast iron pistons, but only ever a new file on an alloy piston. A used file often has shards of steel that can end up embedded in the soft piston.

R gives excellent advice. Can I add a warning? There is a mistake that many of us have made once - once is enough - that should be avoided at all costs.

With a one-piece cylinder and head be extremely careful if you put the loose piston and rings inside the cylinder. Do not push the piston up to the top! If the rings go over the top of the bore they will pop out into the combustion chamber, and getting the whole thing out again is extremely difficult. It's one of those "oh no" moments.

Have fun.

Leon

[robbsa]

99% sure it’s alloy judging on the weight, colour and corrosion on it. I’ve ordered some stainless wool and will go gently at it with a sharpened lolly stick this weekend to try and remove the carbon. Thanks again for the help guys, although I have plenty of workshop experience doing other things and tinkering with engines and bikes that are less precious, I want to get it right on this one first time due to the age. All the tips and help is appreciated.

Feel like progress is good at the moment.

[Mark M]

Sorry if you've thought of this already but do measure the bore and piston and make sure they are a suitable fit before you spend a lot of time cleaning it up. One of the problems with part dismantled projects like this is that the components that come with it aren't necessarily the right ones. I think we've all made that assumption, I definitely have!
REgards, Mark

[robbsa]

Thanks for the word of caution, I’m 99% sure it’s the right one but I will check as suggested to be on the safe side.

[robbsa]

Stainless steel wool arrived and piston came up nicely.

checked the bore again, and there are a few tiny spots of corrosion in there. may have to get it honed. what do you think?

I still need to double check the bore diameter and piston.

[R]

I still need to double check the bore diameter and piston.

Do that before doing ANYTHING.
Once you hone it and then find the clearance is now excessive, its too late... !!
Which then throws up the problem of finding a new piston, and getting it to a suitable running clearance.

It is permissible to use a bit of emery to polish out slight spots of corrosion in the bore,
as long as it is thoroughly cleaned/washed out afterwards. Use a bit of tissue paper to swirl
around in there, and see if it comes out dirty will tell you when it has been cleaned enough.
The last thing you want is bits of abrasive left on the working surfaces.

A big decider towards needing a rebore or not is if there is a wear ridge up at the top of the bore, at the
top limit of where the piston rings travel to. If you can feel this with your thumbnail, it may be too much.
The danger is the piston rings will catch in there, and break.

Adding a slightly thicker gasket at the base will/may help in this respect, if the rings don't quite reach this region.
Honing just the top reach of the bore likewise, although this has to be done carefully so as to not add to the problems.
have fun.