1946 VH 500 Restoration

[KenS]

I received my new JP Piston (JP 0797 + .060) this morning and the included instructions states the piston to bore clearance, measured at he bottom of the skirt at right angles to the gudgeon pin is .004 (0.10mm)
This is different that the .006-.007 that I see is recommended in previous posts. Question is, which to use to have my cylinder bored & honed?

[Roger Gwynn]

Use the original clearance of .005-.007

[SEDoan]

It looks like both could be correct for 500 solid skirt. JB Nicholson says 0.007" on the thrust face below the rings (top of the skirt) and 0.0045" at the bottom of the skirt. This matches the pistons I've used that are slightly larger at the bottom of the skirt. Waller says 0.005-0.007 both top and bottom. Both pistons I've had the pleasure to seize are scarred at the top of the skirt below the rings.

[nevhunter]

Tapered and cam ground with the Biggest dia at the bottom of the skirt at right angles to the Pin.. That's where you take the size measurement. Solid skirt Particularly FORGED ones need more clearance. It's better to rattle a bit when first started than NIP UP at any stage. Silicon in the alloy can reduce thee coefficient of thermal expansion. but also makes the alloy hard to machine. Nev

[KenS]

Thank to you guys and with a bit of time on my hands on this nippy 22 F or -5.5 C morning here in Texas, I went down to my workshop and set out to educating myself on the potential reason of what caused my heat seize issue, especially since Roger pointed out the wear on my old piston picture was in an unusual spot. After learning where to measure the piston to measure the piston to bore clearance, I realized I had made a rookie mistake: I had measured the piston diameter above the top ring, and not the bottom of the skirt, therefore provided incorrect measurements.

I measured both the original Heplex piston and the new JP piston. In doing so, I believe I uncovered the reason for my heat seize: The diameter just below the gudgeon pin is .001" greater than the skirt diameter, thus it only had .002" clearance. I can only conclude it was a defective piston?

A noticeable difference is the weight, 434 grams vs. 511 grams. A 17,7% increase!

[KenS]

UPDATE: Since I will not have sufficient time to have the bike running before I take it to be inspected and cleared by our State Police in order to register it this coming Thursday, I reassembled it minus piston, push rods and valves. It has to be a complete vehicle, but does not have to be running.
Here she is, loaded up on the restored/modified trailer in my workshop.
The bike weighs 355 Lbs. without petrol, Bike and trailer 625 Lbs. that includes a 72 Lb. tongue weigh. It tows great.

[chris.shearwood]

Hi Ken,
Your bike is looking good. Just to be safe, I hope you add a few more ratchet straps before taking it anywhere on the trailer!
Regards, Chris

[KenS]

Hi Ken,
Your bike is looking good. Just to be safe, I hope you add a few more ratchet straps before taking it anywhere on the trailer!
Regards, Chris

Chris, each ratchet strap is rated for 550 Lbs. I will be adding two one each side of the rear. The front wheel is not going anywhere in the wheel cradle.

[david.anderson]

Ken
From what I understand Texas is hot, similar to some of our Australian conditions so my experience may be relevant. I have owned Ariel singles since 1972 and have done well over 200,000 miles on one of them which has meant numerous rebores and rebuilds. I now have a collection of several VHs. I have used various pistons over the years including Die-Cut Y alloy, Heplex, Polson, Cartledge, Omega (both those available from the club as well as earlier versions supplied by Bob Metson), Special (forged) Pistons Melbourne, and JP pistons. I have had had several of those brands nip up when bored at .005” or .006” which was recommended to me at the time. In fact every piston that was bored at less than .065” nipped up at some stage. I now bore to .0065” - .007” bottom of the skirt in an iron cylinder and have not had a problem since.
A few years back I knew an employee of JP who advised me that their most complained about piston was their 7.5 VH piston, in fact I was told that particular piston was responsible for 75% of their complaints. The grind of that piston was being changed at that time to try to solve the problem. Not long after that JP was taken over by Nornda Automotive and my contact sought employment elsewhere so I do not know if the complaints continued.
I have only used 9 to 1 JP Pistons, currently in 2 of my bikes and they have been bored at .065-.007” without any problem.
David

[KenS]

Ken
From what I understand Texas is hot, similar to some of our Australian conditions so my experience may be relevant. I have owned Ariel singles since 1972 and have done well over 200,000 miles on one of them which has meant numerous rebores and rebuilds. I now have a collection of several VHs. I have used various pistons over the years including Die-Cut Y alloy, Heplex, Polson, Cartledge, Omega (both those available from the club as well as earlier versions supplied by Bob Metson), Special (forged) Pistons Melbourne, and JP pistons. I have had had several of those brands nip up when bored at .005” or .006” which was recommended to me at the time. In fact every piston that was bored at less than .065” nipped up at some stage. I now bore to .0065” - .007” bottom of the skirt in an iron cylinder and have not had a problem since.
A few years back I knew an employee of JP who advised me that their most complained about piston was their 7.5 VH piston, in fact I was told that particular piston was responsible for 75% of their complaints. The grind of that piston was being changed at that time to try to solve the problem. Not long after that JP was taken over by Nornda Automotive and my contact sought employment elsewhere so I do not know if the complaints continued.
I have only used 9 to 1 JP Pistons, currently in 2 of my bikes and they have been bored at .065-.007” without any problem.
David

David,
Thanks very much for sharing you experience's. Your timing could not have been better as I received a call from our police yesterday afternoon informing me my inspection is being postponed for a week due to weather. So I disassembled the top end again and I am on my way in an hour to drop off my piston & barrel to be bored. I had in fact decided to start at .006", but now, I'll just have it bored to .007" and be done with it.
Thanks again mate.