Piston peg repair

[Kelly]

Is it possible to repair a piston peg , that has hole but peg is missing thanks

[rossclark]

It's possible but if it's gone where did it go and what other damage did it do?

Wouldn't it be easier and safer just to get a new piston?

[Kelly]

Piston is nos but has only one peg hope to fix it if i can , just need to how and what material to use

[Knowledge]

A needle from a roller bearing (small end bearing?) is a good material for making ring pegs, but the problem is getting it to stay there.

There are some fantastic glues on the market, but I would struggle to recommend one that would guarantee that the peg would remain there.

If this is a three ring piston, and the ring peg is missing from one of the lower rings, it might be safer to run the piston without the ring. I would still prefer to replace the piston, especially as it will be going up and down barrel 100 times a second at full chat.

[Sticky]

A NOS incomplete piston is a broken piston.

I've re-pegged with needle rollers before for racing but it's not a great idea. For the price of another piston is it not better to get a new one with all the bits?

[Kelly]

Thanks for your help ill give it a bit more thought , ive access to all types of welding , brasing ect so hold in place should not be a problem , famous last words lol

[rossclark]

A NOS incomplete piston is a broken piston.

Agreed, get a NNS one and save yourself (some of) the worry...

[Adam_Winstone]

The issue of 'which ring?' peg, that Knowledge raised, is an important one. Knowing what type of piston it is and which ring's peg is missing are key to being able to answer the question.

A pal of mine had a Stage 4 tune done to a SIL 200 barrel and made the comment of being happy to pay the money to upgrade the piston to an Asso thin ring piston, to which the tuner (probably in the top 5 most respected tuners in the UK) said that the Asso piston was horrible when compared to the SIL's original Mahle 3-ring piston. His reasoning was that; 1. the Asso's alloy was not as good and that the piston was far more likely to suffer seizure, 2. the Asso was far more prone to cracking from transfer windows, 3. The Asso was no more likely to suffer ring breakage if the exhaust width and shape was factored around using the Mahle.

... to add to that, additional benefit would be gained by removing the 3rd (bottom) ring of the Mahle's 3 rings as the extra ring simply resulted in more friction, which meant more friction, more heat and more wear.

This top end has proven itself over and over by covering thousands of miles and showing a clean pair of heels to some larger capacity and higher spec machines, which you would expect when you know who tuned it.

In light of the above, knowing what the piston is and which peg is missing becomes pretty important.

Adam

[Warkton Tornado No.1]

Quite why a piston shouldn’t be re-pegged is a mystery to me, if the same principle of pegging can be followed &/or even improved upon by anybody with any engineering competence.

Re-pegged pistons that I have done have never been known to fail.

The manufacturers of pistons use a wire of a known metallurgy & size for the interference fit that they rely upon. They do not use needles from roller bearings as suggested by many. Manufacturers use wire fitted through to the inside where they bend over the excess of the peg.

They usually use a hard drawn wire that will have similar qualities to ‘Silver Steel’ although Honda used brass pegs in their pistons that many of us used for a few years. They regularly wore out.

The pegs are then finished flush with the piston most commonly during the final machining process.

A pal of mine had a Stage 4 tune done to a SIL 200 barrel and made the comment of being happy to pay the money to upgrade the piston to an Asso thin ring piston, to which the tuner (probably in the top 5 most respected tuners in the UK) said that the Asso piston was horrible when compared to the SIL's original Mahle 3-ring piston. His reasoning was that; 1. the Asso's alloy was not as good and that the piston was far more likely to suffer seizure, 2. the Asso was far more prone to cracking from transfer windows, 3. The Asso was no more likely to suffer ring breakage if the exhaust width and shape was factored around using the Mahle.

... to add to that, additional benefit would be gained by removing the 3rd (bottom) ring of the Mahle's 3 rings as the extra ring simply resulted in more friction, which meant more friction, more heat and more wear.

The Mahle pistons are good products similar to AE Hepolite & using just the top two rings gives a convenient oil reservoir in the redundant ring grove. This was common practice in the Seventies.

Personally, I have never used an Asso piston & would always try & seek out an alternative.

[rossclark]

The OP said it has one peg and one missing. This would suggest a two ring piston.

I can understand that someone with a fair degree of engineering skill might be able to make a satisfactory repair. The fact that the OP is asking suggests that he may not have any experience in this type of repair (no offence intended here).

It can be repaired but given the cost of a good quality replacement piston like the Mahle is it really worth the effort just because it's 'NOS', albeit defective old stock?

[Warkton Tornado No.1]

This Forum exists for friendly, healthy debate & is a source of information, often given freely by those more experienced users that feel that they can.

Advice is being offered here, but it is also opinionated:

It's possible but if it's gone where did it go and what other damage did it do?

Wouldn't it be easier and safer just to get a new piston?

My own advice was also opinionated, but possibly a better attempt in answering the question:

Quite why a piston shouldn’t be re-pegged is a mystery to me, if the same principle of pegging can be followed &/or even improved upon by anybody with any engineering competence.

Re-pegged pistons that I have done have never been known to fail.

The manufacturers of pistons use a wire of a known metallurgy & size for the interference fit that they rely upon. They do not use needles from roller bearings as suggested by many. Manufacturers use wire fitted through to the inside where they bend over the excess of the peg.

They usually use a hard drawn wire that will have similar qualities to ‘Silver Steel’ although Honda used brass pegs in their pistons that many of us used for a few years. They regularly wore out.

The pegs are then finished flush with the piston most commonly during the final machining process.

However, checking the thread:

The OP’er (Original Poster) never stated the Manufacture of the piston or number of rings.

Mahle was not mentioned until Adam spoke of them. That said, as far as I am aware, Mahle pistons produced specifically for Lambretta have either two or three rings.


The OP’er went on to say:

Thanks for your help ill give it a bit more thought , ive access to all types of welding , brasing ect so hold in place should not be a problem , famous last words lol

Presumably, we are all grown-ups capable of making our own decisions & Kelly can analyse the responses for himself to make a wise choice.

Phew!

[rossclark]

I'm sure he will, despite our divergent opinions.

[Kelly]

And I will but maybe i ask the question in the wrong way i maybe should have ask what material and hows it fixed in place but the someone will still say buy a new one