ES2 pistons

Hi Dan

Based on RGM's website it looks like you could fit either but the later ones give a slightly higher CR.

Andy

Hi Dan,

The ES2 1955 you have, needs a piston which is stamped at the inner side with the number W10226, according to the Hepolite manual, with a compression length of 1-11/32" and a full length of 2-7/8", and a compression ratio of 6.8/1.

In comparison, the 1956 piston has stamped the number W13346, with a compression length of 1-3/8" and a full length of 2-19/32", and a compression ratio of 7.1/1.

Hope this can help you.

Hi Dan

I have a modified 16H piston in my '51 ES2 giving about 8.2:1. I don't think you'd notice the difference between those two pistons unless you put the bike on a dyno. The only thing you might find is a difference in weight could have an effect on the balance factor of the engine, and in turn vibration.

I have used JP Pistons without any trouble, and I'm pretty sure Mike Pemberton uses GPM, so it's probably not a lot in it. Although I'm sure some people will tell you not to use anything other than an original hepolite, would be nice if you can find one!

Andy

Hi Dan,

The one you missed on eBay is perhaps the same I purchased for GBP 97, having bid up to GBP 102.

Anyways, as I own a Model 18 1947, it is the right one, since the seller has put a photograph showing the inside of the piston cast in with the number 4517, which is the correct.

Don?t forget that your Norton need a longer piston (2-7/8" instead of 2-19/32" of mine). The reason for that is that the longer piston is suitable for those engines that features a reduced flywheel diameter.

Just in case, I bought the last week a GPM piston from British Only Austria, thinking not to find an original. Once I get both pistons, I will share the difererences, if any, of the pistons. Also the weight of the 4517 one, so you can compare it against others you may purchase.

Hi Dan

It might be worth putting some blu-tack on the top of the piston and turning the engine over to check if the valve pockets are even needed. They weren't on my ES2 so all I had to do was turn a bit off the skirt to clear the flywheels. However my head has badly recessed valve seats, so over the winter I'll get new ones fitted and this could mean removing the piston and putting in the valve pockets.

Worth a look though

Andy

Hi.Dan i have a 1955 es2 with a wellworthy cylinder head on that was fitted to that year perhaps its because of that the pistons were different. i had a new piston for mine and on fitting it when i turned the engine over by hand the piston would catch on the cylinder head found out my old piston had a chamfer on the edge of the crown and the new one didn't i removed piston had the chamfer machined in so as it was same as the old one and put it back together it didn't catch its all ok running great.

Previously Dan Field wrote:

Hans, that was the one! At least it went to a club member! I'll be interested to know how the Pistons compare.

Dan

Hi Dan,

Now, I have both the GPM and the Hepolite pistons. Not expert in upolading photographs, for the moment I will give you some details.

The 4517 Heplite piston .040" has a weight of 431 grs. complete, and the GPM 444 grs., being a .020" one.

The gudgeon pin of the Hepolite is lighter: 82 grs. against 100 of the GPM. The GPM has a reference-Nr. 7915, which is suitable for the ES2 model 1956/58, with a compression ratio of 7.1:1.

Having both pistons the same length, the gudgeon pin hole is displaced down respect the Hepolite one, and the skirt is flat at the bottom.

Valve pockets at the GPM are cast, instead of the Hepolite?s milled.

There are more differences, but you are lucky not having bought my piston, which is not suitable for your ES2.

The austrian British Only Austria has more for sale, and also put on eBay.

Previously Dan Field wrote:

Andy, I missed one on eBay at the weekend .... forgot to set gixen to do a sneaky snipe! Went for about £95 I think. Mine has a 16H piston fitted atm but the handy work incl the valve pockets were done by hand and I don't trust it, so would rather be safe than sorry! I'll give Mike a ring tomorrow.

dan.

try bantam john i will be suprised if he has not got a hepolite piston for your bike.

i,ve used him before and he has always come up trumps.

only last week i bought a model 19 piston off him and recieved it two days later.£125.

tony

Hi Dan

Yes-It's a 16H piston. Any info you could give me from yours would he helpful.

I seem to remember the BSA pistons are the right bore and a good crown shape but the wrong compression height, you have to machine a couple of mm off the bottom of the barrel to make them work properly, but I think you can get up to around 10:1 with them, depending on how much you shorten the barrel. The 16H piston should give about 8.5:1 that is plenty for my intended use.

Thanks again, glad you are sorted

Andy

Thanks for that Dan.

I have spoken to Mike Pemberton and John Harding over the last few days, couldn't find two more helpful guys, really know their stuff and are only too happy to share what they know.

The B44 scrambles piston can be used by machining about 3mm off the bottom off the barrel (and shortening pushrods and tubes by the same) to give about 9.5:1. By my calculations only machining 2mm off the barrel would give about 8.5:1 and 1mm would give 7.5:1. Mike reckons you can take a road going single up to 10:1 with no problem, John Harding reckons 10.5:1 is about the limit!

I don't want to push it too far as my number one requirement is reliability! I am also reluctant to modify the engine in such a way that I can go back. I also have a perfectly good +20 16H piston and a fairly recent re-bore. John only had B44 pistons in +80! With this in mind I decided to try and make use of the 16H piston.

I set the piston up on an angle plate and started cutting, first attempt I took 0.100''. Upon re-assembly the piston and valve just touched at TDC, I took another 0.050'' and I now have aroung 0.035''-0.040'' clearance, MP suggested 0.030''-0.040'' would be OK.

There looks to be plenty of meat left on the crown as the deepest part of the pocket is out over the rings. I'm going to take it to Kempton Park tomorrow and show it to John Harding to see what he thinks. If its OK I'll do the exhaust pocket in the same way, this one doesn't need to be as deep.

I've attached a couple of pics to show you how it worked, luckily I found a fly cutter that was about the right radius to leave 1mm all around the valve.

Thanks again for your pointers

Andy

And a pic of the finished pocket. Don't seem to be able to add two pictures to the same post!

Hang on guys !!

Before you get too carried away make sure you get all the information before you start using high compressions. The maximum compression you can use is dependent on several factors mainly the fuel used, the materials the cylinder head and barrel are made from for heat dissipation and the mechanical design of the engine in general. Back in the 1960s and 70s when there was 5 star petrol it was easier to do this but the current super unleaded is not quite as good as the old 4 star. The cast iron type ES2 engine would beup to8.5 to 1 for road use, the bi metal Welworthy Alfin type 9.5 and the all alloy head 10 to 1 on this fuel. The early push rod engines have short cylinder studs and there would be a possibility the barrel could fracture just above the flange if the compression is too high. It is virtually impossible to get a high compression with a side valve unless you supercharge it. If you get valve float it is always the exhaust one that will hit the piston unless there is a major mechanicalfailure elsewhere. You should be looking for about 60thou clearance on the exhaust valve at top dead centre but be aware TDC is not necessarily the nearest point of contact between piston and valve. The B44 piston has the same gugeon pin to crown height as an Inter or long stroke Manx but the pin diameter is .75" against the Norton .875" and is much heavier than an ES2 so the balance factor of the flywheels will need changing. Phil Irvin's Tuning for Speed is the bible for this info so if you can get a copy, do so. Regards, Richard.

Hi Richard

I was surprised when Mike said 10:1 would be OK on an Iron engine, if I was going that high I would want to be running on super green all the time - not always an option.

I checked the compression last night and I have about 8.6:1, this should be fine. Modern fuels get a very bad rep but they are a lot better than the post war pool petrol.

Regards

Andy

Hi Andy/Dan,

Andy, sorry I didn't get to talk to you today at Kempton. Yes I tried running my cast iron Inter on 10 to 1 back in 1974 and it would only do a couple of short circuit laps before detonation set in, even with leaded petrol and openvalves. 8.6 should give you good performance and reliability, anything higher with cast iron will be asking for trouble. If you have any valve timing figures for your new cams that would be of interest.

Dan, methanol is best but on the track you will be lucky to get 25 mpg and you need to shop around for the best price. I have been using it for track use since 1989 on and off and you need to use castor oil as it will contaminate mineral and probably synthetic oils. The only limit with methanol is how strong the engine is, as the explosive pressure is around 400 psi at 14 to 1 compression !

Regards, Richard.

Hi guys,

Why not see what I posted on October 02?

There are many details about the pistons.

I can also provide more info, because I have a Hepolite catalog.

Cheers,

Hans from Chile.

Thanks Hans, all useful information.

Richard, the info for my cams is as follows:

Inlet valve: -

Inlet valve opens at 60 to 65 degrees BTDC

Maximum lift 0.425 at 99 to 104 degrees ATDC

Exhaust valve: -

Exhaust valve closes at 55 to 60 degrees ATDC

Maximum lift at 102 to 106 BTDC.

Note: - On a long stroke engine max lift at up to 117 degrees BTDC on the exhaust valve gives good results

I have got the inlet at max lift at 102 degrees and the exhaust max lift at 115 degrees. There is nearly another 0.125 inch of lift at the valves! And considerably more overlap, hence the need for some valve pockets.

Regards

Andy

Hi Andy,

Thanks for the cam info. They look as though they are quite high performance ones and I wonder if thepockets you can get in a 16H piston will be enough for the extended lifts. Keep us posted on any progress and I hope they work out O.K.

Regards, Richard.

Hi Richard

After machining the pockets I took the piston to Kempton with me and John Harding took a look and said it looked fine so I have fitted it and am confident it will be OK. They are quite deep but as the deepest part is out over the piston rings there is still a fair amount of thickness left on the crown.

I started it up and took it for its first ride today, 9 miles to the petrol station and back, it sounds incredible but I must get some decent ear plugs, it is rather noisy! It started second kick, ticks over and pulls like a train at low revs which I was a little concerned I might lose with the big carb and hot cams. I need to do a bit of running in before I really test it but it seemed OK. It goes a bit flat around the mid throttle range but I checked the plug when I got home and it looks to be running weak, I'll lift the needle a notch before I try it again, not surprising as it's a new carb and something non standard so is likely to need some setting up.

So far so good

Andy

Hi Andy,

Sounds like you are sorted! I would think you should be able to hit 90 mph but it might be a good idea to gear up so you have a high cruising speed at sensible revs. The only problem you might have is if you miss a gear so if there are any gearbox issues, take care. Get back to us when you have chance to put some miles on it and can compare it with the old set-up. One thing I found was that the extra speed showed up more road and handling imperfections that I hadn't noticed before! ATB, Richard.