Piston Broke

[TVS44]

Piston broke

Seems the `piston broke` has generated a lot of advice and info,
£12 is a bloody good subscription when it involves all those eager to help.
cheers

 

[AndrewD]

Seems the `piston broke` has generated a lot of advice and info,
£12 is a bloody good subscription when it involves all those eager to help.
cheers

VERY good value, particularly when you don't need to pay to post

 

[AndrewD]

There is a cheap head on eBay if you after one in the end (Sherlocks were a bit steep!)

EBAY....

 

[garry a]

if it was me i would just flush out sump fit new piston and rings etc check valves get it running again check ign timing with strobe and mixture and after a run check the compresion's and plug colours.no point in splitting engine its got a gauze and paper filter change oil and filter after a bit if all is ok. but thats just what i would do

 

[Ugly Cow]

My understanding is that one piston is heavier than the other?
Does it matter?

Not weight but size, and yes it does matter,(get the correct piston grade for the cylinder) these engines are mass produced, they churn out barrels and pistons of varying sizes, so all they do is match a piston to the barrel, too large a piston and it runs the risk of siezure, to small and you get 'piston slap' hence the expensive trade in 'blue printing engines'.ie: as the engine designer wished all tolerences and weights to be.

Let us know what you do and the outcome
UC

 

[(RIP) Kaister]

My understanding is that one piston is heavier than the other?
Does it matter?

Not weight but size, and yes it does matter,(get the correct piston grade for the cylinder) these engines are mass produced, they churn out barrels and pistons of varying sizes, so all they do is match a piston to the barrel, too large a piston and it runs the risk of siezure, to small and you get 'piston slap' hence the expensive trade in 'blue printing engines'.ie: as the engine designer wished all tolerences and weights to be.

Let us know what you do and the outcome
UC

Piston weight matters a lot

they have to be within a few grams of each other when complete with rings,pins etc - or the engine will feel rough

its called 'balancing'...

 

[magno]

I've seen exactly this type of damage on a 1200 which was dropped hard on the cylinder head. My thinking was that there's some movement in the barrel studs and just enough flex to break the brittle piston rings. A cylinder head cover/head is easily replaced. No visible damage to the crown so it's all put back together and runs ok........for a while. Then you get what you see in the pics.

What I'm saying is that this isn't necessarily a timing/mixture issue - but obviously check this when you get it running again.

 

[Smug]

Seems the `piston broke` has generated a lot of advice and info,
£12 is a bloody good subscription when it involves all those eager to help.
cheers

Almost as good as asking down the pub

 

[Ugly Cow]

Piston weight matters a lot

they have to be within a few grams of each other when complete with rings,pins etc - or the engine will feel rough

its called 'balancing'...
Kaister is offline Report Post Reply With Quote

Piston rings, gudgeon pins are not wieghted niether are mass produced pistons
I used to work for a major engine manufacturer and can state my previous comment is a fact, the letter denotes size NOT wieght.

 

[The Grey One]

A little knowledge...................

Piston weight matters a lot

they have to be within a few grams of each other when complete with rings,pins etc - or the engine will feel rough

its called 'balancing'...
Kaister is offline Report Post Reply With Quote

Piston rings, gudgeon pins are not wieghted niether are mass produced pistons
I used to work for a major engine manufacturer and can state my previous comment is a fact, the letter denotes size NOT wieght.

I spent 30 years fixing (amongst other things) Citroen 2 cylinder engines. Air cooled flat twins with pistons a barrels that came in matched sets. Don't know about BMW pistons but the Citroen ones certainly were weighed and then matched for weight. Only sold in pairs complete with barrels. But then Citroen were,in days gone by, a company run by engineers. If any of you want chapter and verse about the virtues of their air cooled flat twin engine just post a few rude remarks on here and I will give more details to help you out of your ignorance!
Only people who would fit one piston to a Citroen flat twin were those who wore spurs and a ten gallon hat. The matched pistons were required to help the engine run as smoothly as possible. Unmatched ones could, and did, cause noticable roughness in running.

Was the "major engine manufacturer!" Perkins by any chance

John

 

[cookie]

sounds like citroen couldn't reliably make pistons that weighed the same to me

 

[The Grey One]

sounds like citroen couldn't reliably make pistons that weighed the same to me

Who can? There will be variations albeit small in any mass produced product. Sounds more like the engineers in charge knew their stuff and made sure that any slight miss match was kept within fairly close tolerances. The engine did,after all,develop peak power at 7,000 rpm and was safe to quite a bit higher than that.

John

 

[(RIP) Mark H]

I think the smoking gun is .......

" yes it was pinking quite badly but no more so during previous rides"

That's the cause of your holed piston, make sure you eliminate the pinking after your rebuild,

I wouldn't split the engine on this one, look at ways of collecting the bits, magnet secured (very secure) to end of flexy rod will get the metal, oil/ paraffin, flushing oil, any left alloys / debris will sit there or be picked up by gauze / filter.

 

[warmshed]

In the past the trick was to put a dab of grease on the crank/flywheels then rotate it. It is supposed to pick up bits in the crankcase. never tried it but it was common advice.

 

[(RIP) Kaister]

Piston weight matters a lot

they have to be within a few grams of each other when complete with rings,pins etc - or the engine will feel rough

its called 'balancing'...
Kaister is offline Report Post Reply With Quote

Piston rings, gudgeon pins are not wieghted niether are mass produced pistons
I used to work for a major engine manufacturer and can state my previous comment is a fact, the letter denotes size NOT wieght.

oh dear .

Don't you think that some bod in the design office has calc'ed the sizes to weights and figured out the matches and checked they are with reasonable tolerances of each other. ?

 

[magicstu]

The pistons are usually fairly close, providing they are from the same batch, on most suppliers.


It's the con rods and crankshaft/flywheel that makes the biggest difference when balancing up an engine.

 

[(RIP) Kaister]

no its not - the major forces are on the piston.

the nearer the components are to the centre of rotation - the less influence they have on rotational imbalance

 

[magicstu]

I meant they(pistons) are easy to balance,as they are fairly close out of the box, the crankshaft is a dynamic balancing job, and the con rods you balance both ends individually.

 

[Ugly Cow]

I meant they(pistons) are easy to balance,as they are fairly close out of the box, the crankshaft is a dynamic balancing job, and the con rods you balance both ends individually.

You are correct but unfortunately flogging a dead horse