genuine hepolite piston rings

Because of the peculiarities of my pistons (genuine Hepolite std bore) the gudgeons are tight in the pistons, and have to be heated to install.

Every piston on a British 4 stroke motor cycle I have ever took apart has been the same.

You can do it the way you describe but use a hot air gun on the piston making sure the flow is directed on the thick parts of the casting next to the pin. I was doing this last week on a T120 and it only needed 2 mins of heating for the pin to move freely.

On an 850 I was fitting new hepolite rings to back in the 80's had 3 piece oil control rings that would not enter and I had to shorten them to fit, seems there was a batch of wrongly sized rings as a few other people had the same issue.

1.GPM have a good reputation but you need to make sure their rings are sized for your piston grooves ie width and depth.

2. If you can't find Hepolites then Hastings are a good alternative (same comment on sizing as GPM), do not touch JP of Australia rings or pistons.

Hot air gun will not set the gaskets alight, rags soaked in boiling water works as well but is messy. Hot iron on top of piston also works but that's no good if its at the bottom of a bore.

Previously john_holmes wrote:

Because of the peculiarities of my pistons (genuine Hepolite std bore) the gudgeons are tight in the pistons, and have to be heated to install.

Every piston on a British 4 stroke motor cycle I have ever took apart has been the same.

You can do it the way you describe but use a hot air gun on the piston making sure the flow is directed on the thick parts of the casting next to the pin. I was doing this last week on a T120 and it only needed 2 mins of heating for the pin to move freely.

On an 850 I was fitting new hepolite rings to back in the 80's had 3 piece oil control rings that would not enter and I had to shorten them to fit, seems there was a batch of wrongly sized rings as a few other people had the same issue.

1.GPM have a good reputation but you need to make sure their rings are sized for your piston grooves ie width and depth.

2. If you can't find Hepolites then Hastings are a good alternative (same comment on sizing as GPM), do not touch JP of Australia rings or pistons.

Hot air gun will not set the gaskets alight, rags soaked in boiling water works as well but is messy. Hot iron on top of piston also works but that's no good if its at the bottom of a bore.

Previously roger_wilson wrote:

Previously john_holmes wrote:

Because of the peculiarities of my pistons (genuine Hepolite std bore) the gudgeons are tight in the pistons, and have to be heated to install.

Every piston on a British 4 stroke motor cycle I have ever took apart has been the same.

You can do it the way you describe but use a hot air gun on the piston making sure the flow is directed on the thick parts of the casting next to the pin. I was doing this last week on a T120 and it only needed 2 mins of heating for the pin to move freely.

On an 850 I was fitting new hepolite rings to back in the 80's had 3 piece oil control rings that would not enter and I had to shorten them to fit, seems there was a batch of wrongly sized rings as a few other people had the same issue.

1.GPM have a good reputation but you need to make sure their rings are sized for your piston grooves ie width and depth.

2. If you can't find Hepolites then Hastings are a good alternative (same comment on sizing as GPM), do not touch JP of Australia rings or pistons.

Hot air gun will not set the gaskets alight, rags soaked in boiling water works as well but is messy. Hot iron on top of piston also works but that's no good if its at the bottom of a bore.

hi, I have just purchased genuine hepolite +20 rings from the club shop-members only-still getting round to fitting them.

My genuine original hepolite pistons obtained from a well known old stock supplier had pins that were (an interference fit) to the point that they were heated to extreme and hammered out-wonder what that was all about? I then had to ream the piston pin bores to eventually achieve a warmed sliding fit!

Has anyone else had this issue?

The factory I worked at made aftermarket bearings for AE of Bradford as did Hepolite but pistons and rings, the machine lines for the aftermarket were the old slow low batch production. The high speed production lines suplied direct to Ford etc and were state of the art and the highest skilled operators, the aftermarket side did not have the same attention. Anything made to a drawing is only as good as the machines, operators and inspectors are and even the best make mistakes. So yes I am not surprised you had oversize pins, bound to happen at some point and be missed.

What about freezing the pin?

I have done this on bearing races and it works a treat!

Just a thought.

Kevin

FWIW, I have used many sets of JP pistons without issue. Most failures are from good meaning folks not reading the directions that came with the pistons & instead read the Factory workshop manuals which was for fitting pistons of a different material & very different expansion rates. Consequently the JP would seize due to the wrong clearances used. Not the fault of JP im afraid.

The new Wassell pistons come with the American made Hastings rings as standard. I have found the new Wassell Hepolites to be made more accurately the the NOS orginals I have in both weight & measurements.

This is just my findings, yours may vary.

Skip

I'm with Skip in his views. Any piston problems I have had over the last 49 years of riding brit bikes have only been with Hepolites. Cracks, crowns coming adrift, holes, general breaking up. You really shouldn't have a piston break up 200 miles into careful running in. Sending the remains backgot the response I must have been thrashing it...

My 1960 99 is on std bore, still good and fitted with new GPM rings from RGM with original pistons. It is the sweetest and smoothest Dommie you ever did hear or ride on.

Hi Paul...There are two ways to fit the barrel;

1) lay 2x wooden strips/bars across the crankcase mouth to support the piston. Push the pistons down so they are squarely supported on the wood ....arrange the ringsfor 120 deg. separation. Use 2x piston ring compressors to squash the rings...Oil the barrels, then lower gently the barrel rocking very slightly as you continue to push down the barrel until the rings are all in....tip don't have the compressors too tight.

2) if you want to do it by installing the gudgeon pins after having fitted the piston....(to me this is a more difficult method)it is best to convert the pistons tohave afully floating gudgeon pin. This can be achieved by lapping in the pins with metal polish so they slide into the piston when cold...many modern qualitypistons have this done at the factory . The advantage is that you get a bigger small end bearing surface....Les

If pins go from tight to loose with a little heat then loose pins must go from loose to very loose at running temperature. Be sure that is what you want before you open up those gudgeon pin bosses.

If you are prepared to wait I am sure std 500 rings will turn up. I have some std 99 rings that are of little use since my first rebore,I'm sure there are plenty laying around ,it just needs someone to feel helpfull.

Previously Jonathan Soons wrote:

If pins go from tight to loose with a little heat then loose pins must go from loose to very loose at running temperature. Be sure that is what you want before you open up those gudgeon pin bosses.

So Jonathon every small-end bearing runs far too loosely at running temperatures?....they are quite loose to start with and are made from alloy (and sometimes bronze bushed) that expands more than the alloy pistons are made of. Should we really have small-ends that we have to heat up and fit the gudgeon pin then?

Nope...first of all a cold push-in sliding fit of a gudgeon pininto a piston is not a loose fit...it'stighter than the small-end clearance which has the same diameter and is made with a material that expands MUCH more than Low Ex piston Alloy withno negative consequences........Second most modern quality pistons use this type of fit.....Also, I suggest you readthe great P J Irving's mechanical bible: "Tuning For Speed" page 78 ....this might put your fears to rest.

Les

Les is right, and is backed up by David Fletcher-Jones who ran the R&D at Wellworthy. He can probably supply the right rings: Tel 01425-629184. He tpld me all gudgeon pins should be an easy push fit, and as he advises Rolls Royce Aero engines on piston matters I think he and Les win the day?

Thanks for that information Tom.

I can understand what Jonathon is visualising and suggesting but what is being overlooked is that the piston is eventually heated far more than the 100 Deg C that is required to freea tight gudgeon pin to enable it to be pushed in so the pin will always be slack at running temperatures whatever you do.

In his book, Phil Irving explains that the fully heated working piston will have around 2 thou of clearance for the gudgeon pin so by making the pin a sliding fitonly addsan extra1/20th of a Thouso makes no difference in practice on the total working slackness of the pin within the piston....Les

Previously les_howard wrote:

Previously Jonathan Soons wrote:

If pins go from tight to loose with a little heat then loose pins must go from loose to very loose at running temperature. Be sure that is what you want before you open up those gudgeon pin bosses.

So Jonathon every small-end bearing runs far too loosely at running temperatures?

No. We are not talking about small ends. We are talking about gudgeon pin bosses in pistons. If the gudgeon pin is heated to put it in (as in all my engines) then it will be just right at running temperature (probably by design). If they start out loose when cold then they can only get looser when hot. Only logic, so far. Regarding Phil Irving, I would rather follow him blindly than a lot of other people, but it is better to understand the problem for yourself.

Another point of logic: It does not follow that if one gudgeon pin runs very loose (for whatever reason) that "every small end bearing runs far too loose..." Beware of really wishing people had said what they did not in fact say.

I am waiting for someone to explain why a steel in alloy fit would not get looser with more heat (my only simple claim), i.e why the coefficients of expansion would not remain linear in this case.

No matter how many big names are dragged in (Phil Irving, David Fletcher-Jones) they cannay change the laws of Physics.

any mechanic worth his salt would know that pistons go into a bucket of hot to boiling waster until assembly [a few minutes ]and then the pin goes into the piston easily by hand. hold the hot piston with a glove.

2 thin equal lengths of wood held with 2 bolts to go under the piston to drop the barrels. easy.

Previously eddie_simpson wrote:

any mechanic worth his salt would know that pistons go into a bucket of hot to boiling waster until assembly [a few minutes ]and then the pin goes into the piston easily by hand.

Pistons made today do not need to be heated any more. They slide into the piston easily. I have used the ones from EMGO at work, which are this way. Phil Irving and I say this is a very loose fit (.0025" clearance hot approx.) Very loose is obviously not too loose. A normal fit is .001" for every inch diameter (again according to Irving) and our gudgeon pins are .6868" (2/3 of an inch approx.)

Hi Jonathon....Just to let you know I've lost interest in this thread, once someonefailsto read (orignores) what has just been said and then replies by twisting it all up with gobbly gook, I butt out...I just cannot be bothered to decipher what you mean....Sorry.

For me it's next subject please.

Les