Which pistons are available for my ariel

Singles, twins and fours.
nevhunter
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Re: Which pistons are available for my ariel

Postby nevhunter » Mon Aug 14, 2017 11:36 pm

The only time I used the original balance as supplied, was on an AJS the vibration ended up not particularly good. The shaft lined up perfectly (unusually) more easily than most times. The bore was standard (no sleeving either) with AJS marked on piston minimum clearance on all bearings. I though this one would be smooth. It was OK but vibration evident at the upper end of the normal rev usage. All other motors I've built I have balanced from scratch, doing each wheel separately.
I know that quality engine manufacturers balance flywheels individually at manufacture and use an average rod and piston weight for their figures. As the forging dies wear the rods get heavier until the dies are replaced and the show starts again. I don't know what variation is produced in factor by that approach. If your factor is 65% the variation of actual weight effectively is applied at 2/3rd of actual. at the flywheel. Whatever you do have the factor EQUAL in each flywheel, otherwise you have an unbalanced couple that is entirely avoidable.
If you have a heavy piston/rod assembly ( only the small end component is used) It reciprocates and you can't use a rotating weight to FULLY balance an up and down force unless you employ extra balancing wheels, (or have a SQ4) so it's all a bit of a guess and final factors are arrived at by testing rather than mathematics. 65% is considered a good start point if you have no other GOOD information, for singles. Nev

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cmfalco
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Re: Which pistons are available for my ariel

Postby cmfalco » Tue Aug 15, 2017 3:24 am

Nevhunter,

All fine, but not helpful in addressing the question of interest, i.e. having the weight of a 1928 piston so I can determine the balance factor. I'm in pretty good shape with knowing the theory and practicalities of balancing a flywheel, but what I lack is that one number.

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Re: Which pistons are available for my ariel

Postby nevhunter » Tue Aug 15, 2017 7:13 am

I'm suggesting it may not be a lot of help since the original balancing may not have been that precise, as in the case of the AJS I quoted. This is particularly so in veteran machines which the advert usually says "balanced to perfection" and they are miles out and some makes have no evidence of any balance holes being drilled at all. Lately there's also some quite imaginative figures being bandied about by Guru's who seem to want to reinvent a new wheel as if nothing done in the past was correct. Starting from such a point is not completely valid, notwithstanding my comment above as although no holes were drilled, balance weights were cast in but were obviously considered "good enough" in the as cast condition with inherent variations of how they were machined and what datum was used for locating the casting, and how consistent the result was. I've been balancing engines for over 50 years I won't be trusting an original and only check them out of interest if the motor is proven smooth. Phil Irving has some info But he would never give a definite figure. The best is usually arrived at by trial and error in a test engine., with holes to add and remove small weights. I use 65% for Ariels. Do the twins dynamically. Nev

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cmfalco
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Re: Which pistons are available for my ariel

Postby cmfalco » Tue Aug 15, 2017 3:32 pm

nevhunter wrote:I'm suggesting it may not be a lot of help since the original balancing may not have been that precise, ... The best is usually arrived at by trial and error in a test engine.,
As you suggest, testing to find the optimum balance factor for my Ariel would be best. However, to find optimum that way would require me to remove the engine, disassemble, rebalance and rebuild, reinstall, road test at various speeds, and repeat that process a half-dozen times. Call me lazy, but I'm not interested in doing that. Whether or not it actually is less precise, I'm willing to settle for the balance factor the factory used in 1928. For that, I need the weight of a 1928 piston.

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Re: Which pistons are available for my ariel

Postby Greg.Pawson » Fri Aug 18, 2017 9:02 pm

20190305_055943.jpg
This piston has been used for fast road and track work.
Greg.Pawson wrote:
dave.owen wrote:Has anyone personal experience of running an omega piston.. What is the preferred clearance for fast road work with an all iron engine.

Dave

Hi Dave
I have recently fitted an Omega piston to my 1955 HS.... Skirt clearance 0.003" and am very happy with it...I have detuned the motor back to standard VH.


Adding to the piston info the .080" over Omega pistons complete weight is 450g
Attachments
20190305_060112.jpg
Last edited by Greg.Pawson on Mon Mar 04, 2019 5:33 pm, edited 1 time in total.
Greg Pawson
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1955 HS MK1 Detuned, 1956 HS MK 1

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Re: Which pistons are available for my ariel

Postby Greg.Pawson » Sat Aug 19, 2017 1:15 am

dave.owen wrote:Greg, looks nice and new, how does it perform..is the std clearance sufficient to prevent seizure

Dave


Hi Dave you can check out my Ariel on youtube look for ( Ariel 1955 HS ) I try to upload it to here but had trouble.
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Re: Which pistons are available for my ariel

Postby Greg.Pawson » Sat Aug 19, 2017 1:47 am

dave.owen wrote:Greg, looks nice and new, how does it perform..is the std clearance sufficient to prevent seizure

Dave


Hi Dave check this out....

The sound is not good through my phone mic, induction and exhaust resonating a bit but the engine is happy.

Note the vibration level is really low on the handle bars.
The piston that was in this engine from the last owner was 510g complete .080" over GMP and it had a bad vibration at a good cruising speed.... no speedo.

The Omega piston is 60g lighter and the vibration that it had, has gone.

Greg
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1955 HS MK1 Detuned, 1956 HS MK 1

nevhunter
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Re: Which pistons are available for my ariel

Postby nevhunter » Sat Aug 19, 2017 3:08 am

Running heavy pistons makes it more difficult to get smoothness. A round and round rotating balance can't cancel out an up and down stop and start reaction. You can only get some where near the best compromise. Lightest reciprocating weight possible gives best balance outcomes and lets the engine rev higher without loading the parts dynamically. The SQ4 engine is extremely well balanced with contra rotating shafts, but pistons always stop and start faster at TDC than BDC so a 2nd order balance is not achieved. A horizontally opposed motor achieves this better, but has a rocking couple existing due to pistons not being in the same line, but slightly offset from above. Nev

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Re: Which pistons are available for my ariel

Postby PeterFW » Thu Nov 16, 2017 11:41 am

IMD make pistons for Square 4s and can make pistons to specifications. They are on the net.

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Re: Which pistons are available for my ariel

Postby cmfalco » Sat Nov 18, 2017 4:12 pm

cmfalco wrote:... I'm willing to settle for the balance factor the factory used in 1928. For that, I need the weight of a 1928 piston.
In a second stroke of luck I've now found another person with an original Ariel piston. This one is a new, in the box, complete +30 piston assembly in Canada and it weighs 512 grams compared with the 507.2 grams of the used, standard bore piston assembly that previously turned up in Australia. I can't thank these two people enough.

Correcting for the 6.5 grams that I calculate the extra 0.030" x 3" "skin" on this +30 Hepolite/Heplex 4950 weighs (less the two 1"-dia holes for the pin), if it had a standard bore it would have weighed 505.5 grams. This is within 1.7 grams (0.06 oz.) of the used Australian piston so is near-perfect agreement. Since the owner of the Australian piston said it had some carbon on it I'm settling on 506+/-1 grams as the "official" weight of a stock Hepolite piston assembly (piston, rings, gudgeon pin, and Al plugs) for a 1928 Model C Ariel.

Having now measured twice, I can now cut the flywheel once with confidence. But, before any drilling, I will use this weight to determine the original balance factor used by the factory for my engine once I disassemble the bottom end and have the crankshaft on the rollers.

The rollers have sensitivity equivalent to 0.6 grams at the 4" radius of the flywheels so combining this with the ~1.7 gram uncertainty in the weight of the stock piston I will be able to determine the original balance factor to better than 1%. Assuming I don't find "fresh" rebalancing holes in the flywheels made after the bike left the factory ...


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