Which pistons are available for my ariel

[nevhunter]

I don't know why you would want forged pistons. Most Ariel applications wouldn't warrant them and it is more cost, more weight, and generally more expansion, requiring more clearance. Your numbers are not going to be high volume. either. I have had plenty of good piston castings done. JP uses the conventional 3 piece die, and they say the metal is high silicon which makes them a little heavier than some, but mainly the weight is because they are fairly thick in section. The gudgeon pins should be made of something like EN 29B carburised and hardened and ground with tapered bores for lightness. Nev

[david.anderson]

Brenton
I use a 2/3 ie 66.6% for my singles and don’t have vibration problems. I am running a 9 to 1 JP in my most used VH without vibration. I do know that John Shanks used 70% on the race track. You should also be aware that dynamic balancing is generally not necessary for a single due to the narrow width of the crank, and most dynamic balancing machines cannot dynamic balance a single. It is an easy job to do yourself if you follow the procedure in Tuning for Speed.
You may find that 9-1 is too high for an iron head VH. I am currently running in a 48NH with an 8.5 piston and even with 98 octane unleaded the engine will pink under load up hill so I have to retard a little. I am running my 49 VH at about 8.3 to 1 (a 7.5 Polson piston with .060” removed from the base of the cylinder) and can make the engine pink under load. I am running ½” advance on each of the above engines.
Just a thought but you may be able to find a good used 7.5 piston. Any oversize that you get can be finished back to standard and you could consider turning the base off the cylinder to up the compression a bit if you are looking for a higher com. The 7.5 piston actually gives a better combustion chamber shape than the 9-1 high top. You would have to check valve to piston clearance because that P1 cam has a massive .465 lift, and a lot of lift at TDC.
What are you doing for valve springs. You cannot run the early VS20 as they will become valve bound before maximum lift with that cam, and you will bounce valves with the VS422 springs. The HS springs are no longer available. I just measured the seat pressure of new VS20 springs at 70kg (excessive for anything but roller lifters) and the VS422 at about ½ that figure so I have asked Adrian from Franklin Cam if he can supply suitable springs, hopefully something with about 50kg seat pressure. I have advised him that the fitted length is 1.7” and diameter range and he knows the cam lift. Perhaps you should check valve springs with Adrian also. I posted a two lobe cam to Franklin last week and have requested a P1 grind. I reckon he will probably do both our cams together.
David

[brenton.roy]

Hi David, thanks, I hadn't considered valve springs.
First, Hi Nev, my experience of forged pistons is that they are lighter - maybe because they are stronger, therefore thinner? and much better made.
My first speedway motor had cast Yoshimura pistons which gave trouble, replaced by forged Wiseco's which I only replaced due to time, not wear.
I think they expand more evenly, so allowing closer tolerances.
By choice - with unlimited funds (like that will ever happen!) - would be a good forged piston in a Nikasil bore.
This topic has posts / views second only to Paul's resto of his (awesome) sloper, so it's a topic of interest to a lot of us. It would be great to find some agreement about pistons that we could take to the club for their consideration. I'm very interested in what others think. Perhaps John could help out with a form or something?

David, thanks for your advice. I appreciate it. This is a bit of an experiment for me. I would have found out the hard way that the springs were binding.
I have a later copper head gasket that will reduce the compression a little. If I get stuck, I'll make a base shim, although I suppose this will affect the rocker angle.
I do have the Robbins 7.5 that I could skim down, but I have bought the JP, so will see how it goes. I have a spare barrel.
I also have plasticine, my imagination and access to a mill... Yes, the cam is very high lift. There's a fairly good chance this will all end in tears.
Thanks for the info re springs. I will check with Adrian and hope he can come up with something. Does anyone have a source of HS springs?
So far I haven't done any head work and I will leave this for now. A good start will be 3 angle seats and light porting. I like Vincent's Dellorto. There is a pumper version (phf) that fits in to the classic time frame (round case Ducati).
Wali, you must have overcome all these issues? - what are you using?
regards, Brenton

For cam nuts, the P1 data is below;


Lobe 11 LIFT DUR OPEN CLOSE AREA
Centerline 100.00 ATDC 0.008 376.27 88.33 BTDC 107.94 ABDC 49.75
Peak Open Acc. 0.000308 0.010 369.67 84.95 BTDC 104.72 ABDC 49.72
Peak Nose Acc. -0.000315 0.012 364.21 81. 92 BTDC 102.30 ABDC 49.69
Peak Close Acc. 0.000355
Lift @ TDC 0.2624

0.050 313.03 56.49 BTDC 76.54 ABDC 48.98
0.46944 PEAK CAM LIFT

[brenton.roy]

I've had the sleeve done - with a step to stop it moving. Cost an arm and a leg - I could have bought a new, well S/H motor... But, it's a beautiful job.
The earlier sleeve was confirmed diagonal and so repair work was required. I don't want to think about the thickness of the remaining barrel.
At least now I know why it kept seizing. 17thou is a lot across the bore. Please take this into account re some of my earlier comments re JP's! Anything would have seized.
Nev, they'll only do the crank dynamically. You were right, they will split it and fix a bob weight. I've taken your and David's advice and gone with 67%. This is more work, but they'll check each flywheel, then the pair. Measure twice, cut once?
I've picked up the piston. To be honest, the crown doesn't look much different from the Robbins. The 7.5 JP that was in the bike is a little more rounded, but not significantly. That's a relief. It looks tidy and well machined. While they weren't happy with the 10 and 8 thou clearance, they did do it. There's a "voids the warranty" note on the receipt.
Head next..

[brenton.roy]

I've collected the main engine parts. I've added the balance notes for those who know more about this stuff. There are two dirty big holes where my flywheels were..
I expected them to be on the side of the flywheels, but there you go.
My wife is calling this the million dollar motorcycle, which cracks her up... as she knows I'll have to pay for this twice. Hilarious.
Brenton

[brenton.roy]

A quick update.
Sometimes it takes we Aussie's a little time to come to obvious conclusions. Once assembled, the bike wouldn't start. It was a nice warm day and after what seemed to be 15 or 20,000 kicks, it occured to me to clean the points... (yes, I'm that thick.) In my defence, it did have spark - just not an effective one.

With a real spark, it starts after priming, first kick, every time and idles slowly and evenly. The exhaust note is markedly different, sharper bangs. I can't do much with it until I get some miles on it, but it feels a bit lean in mid range - I'll play with needle settings a bit and see what happens. Changing the slide would be a pain as this is one I've "matched" to the body.

The engine does feel a little rough, but again, it's brand new. I will need a decent ride to see where the vibration has moved to - or if it has moved.
It's definitely quicker on the raod.

I should also say that the piston feels and sounds fine - no knock or slap at this stage. I'll see when it's run in. There doesn't seem to be the tightness and the heat that was there with the old piston.

[nevhunter]

My experience is that a piston with heavy relief like the one you have does not transfer heat well to the cyl wall and will get hot. You will need your clearances on the high side with that type of of piston skirt design. They are that way to reduce friction not transfer heat. If it was a Velo the high oilflow would help, as that is one of the reasons that make did 100 miles in the hour.. Ariel singles do not have good high oil flow rates, so watch out for it nipping up at WOT at speed. Nev

[brenton.roy]

Ride test - Things have settled a little now there are a few miles.
The idle speed is increasing a bit as it beds in, compression is better and a couple of little rattles (inlet tappet) need sorting.
On the road, it's smoother and quieter.
What I thought was a mid range miss was just me not working with the new motor. It does have less torque at low revs and around town. It also needs more use of the advance lever and the throttle. There's a loss of "woofyness" - is that a word? at low speed.
Once I'm underway and moving - I'd guess about 1500 rpm - it's all good. It's just a little busier getting moving.
I'm running a 24 tooth primary sprocket, so I expect to lose a little acceleration and low speed drive.
The other side of it is the ease of moving in traffic. I won't win any drag races, but keeping up is no problem. Riding it in the same way as before, I have found myself sliding past the city limit (60kph) pretty easily, and it's something to keep an eye on. A little roll on saw 80kph much more quickly than usual.
The biggest problem I had - the heat buildup - is gone. The oil tank feels quite cool. Nev, I have 8 thou clearance, so no problems there. There's no suggestion of nipping up. I think the casting shape of the 9:1 is far better than the 7.5:1.
I've still got a lot of miles to do before I can wind it up and see whether the vibration (60mph) has moved, but it feels much freer and better at revving, so I hope so.
So, was it worth it?
Definite yes. I spent quite a bit of money on the sleeve and balancing - that was more about the motor than the tuning. The cost of the stellite and grind for the cam and followers and valve springs - about AU$ 320 (keeping In mind I sent the the worst parts I had) and the 9:1 piston - about AU $165, was pretty reasonable. There was also entertainment value. It was a lot of fun.
I still need to buy a new carb - and am using the standard 1 1/8" amal, with a nice big step to the 30mm inlet manifold.
I'll be very interested in David's findings, as he has a different setup to me.
Thanks to everyone who has contributed thoughts and Ideas, and particularly to David for solid advice and help.
Brenton

[stu.sharratt]

When I was searching for alternate piston suppliers I emailed FW Thorntons in Telford & got this reply...didn't investigate any further so don't know what they are!

Sorry I can't help with the big ends or liner.

We have specially made pistons in stock, £214.58 + VAT and postage.

Best Regards, Duncan

Duncan Rowley
drowley@fwthornton.co.uk

F W Thornton - “The Automotive Parts Specialists

[brenton.roy]

Thanks Stu. I wonder what they mean? Forged? They're nearly twice the cost of a JP.

As an update,
I pulled the VH top end down for a look and a tidy up.
The compression has been a bit lower than it should be. I was starting to worry about broken rings.
I found a combination of things that I could have done better during the original build.
Mostly, the bore was a little glazed and the spigot not sealing properly . The rings were fine.

The inlet valve contact was also marked with a "scratch" from a piece of grit.
I got caught in the mallee when the wind blew up. This is farm land that has coarse sand and it drifts about a bit in summer.
Although I did stop at a mate's and borrow a filter, it was obviously too late.

So, a few hours bedding in the spigot with valve grinding paste, a light hone and valve lapping - and hopefully now it will seal.
The piston looks fine. I was running it rich (200 main) and have just stepped back to a 190 main. The crown was a nice shade of brown and the plug good.
I'm thinking about #14 on this chart? http://www.arielownersmcc.com/members ... spx?id=735
This plug is an NGK B6HS - does anyone use a B7 with good results?

Having got the Amal sorted, I'm about to try a PWK JRC keihin. It's flat slide and 30mm. I'll probably need to make a spacer (3 - 6mm for clearance), but it otherwise bolts straight on. Main jet is a 128 (190 Amal equivalent). You'll no doubt read my complaints about this later.

With a fair bit being written about porting since I assembled the motor, I thought I'd include a couple of photo's for comment.
I've had a little tidy up near the valve seat. Is this enough?
I decided to just trim the edge of the guide and to leave the grind marks for the "golf ball" effect. A big motivator for this was that I'm basically lazy.
The inlet port is 30mm at the carb.
I'm aware that the valves and seats are worn. Either I'll need to stellite the valves and regrind or go for bigger valves.

brenton