hole in piston

[manosound]

Well, I didn't mean to bore anyone, including you. Thanks for providing some interesting reading. Just to torture it a bit more, I liked your point about heating up a particlar point on the piston, like a modal turbulence, as you suggest, maybe due to the hemishere. (Harder to start modes in an asymetric space.)  It seems the right piston is trying to go the same way.

Richard L.

[MG]

Not boring for me at all, failure analysis is a very fascinating thing (although rarely a nice one for the owner  ).

This is an effect well known with hemi engines, as to what the cause is, is only speculation though (and probably not very well investigated, since hemi engines are not really state-of-the-art any more, people from the USA might disagree there    ). Asymetric and roof-shaped heads are not known to be prone to this, at least I've never come across it nor read anything about such damage in relevant literature. The idea of modal turbulence is interesting though, maybe with high cylinder pressure moving the modal frequency to the "correct" levels to match the combustion process 

[trevinoz]

Lowbrowbsa,
                       You need to pull your engine down completely and clean all of the aluminium particles out of it.
You would be probably better off with 8:1 pistons. I went down the high compression path back in the 60s with pistons like yours. Bike pinged badly on Super of the day and would only run properly on expensive high octane fuel and then only until the barrel broke away from the flange.

  Trev.

[chaterlea25]

Hi All,
Yup!!! I have had to rebuild a couple of T140 Triumph's that did their pistons in 
The particles of alloy went everywhere, some even rolled into snowflakes by the roller bearings
and they had made their way throught the oil return system to the tank !!!!

On T140's I believe the trouble is fuel starvation usually caused by running with only one fuel tap on
ask the owners which tap they use and its the cylinder furthest away that melts down
I think it must be something to do with vibration at certain revs that causes the starvation, as there always seems to be plenty flow at a standstill

The BSA pistons in the pic look like 10.5's there are some on ebay to compare pics??
As Trev says 8 or so to 1 are enough for modern fuels

Oh Yea, the T140's all distorted their cylinder heads when this happened them 
So the engine internal temps must be very high before the pistons give way

John O R

[cus]

Holy Crap!
I ran my T140 on 1 tap for 5 years,
must have got lucky,
great reliable bike....not so good handling!

Cus

[kommando]

Think this link would be a good read, posted in response to a request for info on a holed Goldie piston.

Looks like pre ignition possibly caused by a hot spot. Could the hot spot be the exhaust valve edge in the center.

http://www.contactmagazine.com/Issue54/EngineBasics.html

[lowbrowbsa]

cheers komm thats a good read

[dpaddock]

The appearance of the piston crown is typical detonation. See these reference links:
     micromotorfactors.co.uk, and bmwvmca.org

David

[manosound]

David,

i'm interested in reading the articlcles but the first link seems not to exist and the second is the general site for the BMW club and I can't find a reference there.

Thanks.

Richard L.

[townsends20]

hi
  I run my rgs on 10.5 to1 and after a complete re-build (still running in) I am very conscious of burning the pistons out so I set the carb to run a bit on the rich side and now using BP ultra.
you could check the points cam to make sure the gap matches on both cyl  if not it could give you an imbalance in your timing also are you running on twin carbs  if they are old it doesn’t mater if they are matching if the slides ect. are worn they will not run perfect, also air filters I think are a must that looks like a very dusty place to test all your hard work.
    Bike looks great how long did it take to build.

              Steve.  UK 

[dpaddock]

Richard L.: I sent you the links directly to your email address. Please advise.
 
David

[Rocket Racer]

cheers guys mg the hole was bigger on the inside but no damage to anything else valvers are good heads good boars still got hone marks i think i just got un lucky with these pistons
ive been serching and i think ill go jp 9:1
on a positive note this is all part of owning the bsa its great to ride and working on it is  as much fun  
thanks all for your imput much apreaciate it  

I appreciate some people like JP's but I had nothing but trouble with them on my norton atlas, kept seizing, I went through several pairs of and heard a lot of other similar stories. Won't ever use them again! my preference would be some wiseco's from cake street and I pick up low mileage or new 8 or 9 to 1 NOS when ever I see them at a fair price. I'm running genuine BSA pistons in the road rocket, they are lovely and light.

ps I have a set of 10.5:1 just like those and will put them in a methanol motor...