aluminum cylinder

[dogbone]

I purchased an aluminum 535 piston & jug. Are the head torque  spec's the same ?
The expansion rate of the old cast unit vs the aluminum must be different.

[Travis]

 The answer to your question is the torque value stays the same. The torque spec for cylinder head nut is 285 lb-inch.

[ace.cafe]

Hey Dogbone,
Which piston did you get with that jug, and was the bore diameter already set when you bought it, or what?

The reason that I ask, is that the forged pistons need alot of room in that bore, about twice as much as the normal clearance. Or else you can have seizure issues.

If you have any questions about any aspect of putting that piston and jug on there, just ask. We don't want you to lock up that motor!

However, if you bought them as a set, with the bore already done properly for that piston, then you're ok. Measure the skirt  diameter from front to back on the bottom of the piston, and measure the bore diameter. Accurately.
For the forged piston, you should have .006" larger bore diameter than the piston skirt diameter measurement from front to back at the bottom of the piston. You might be able to get away with .0055", but that's on the tight side for that forged piston, and you'll have to be real careful breaking that in.

For the normal cast piston, you can use .003" or .0035" clearance, measured the same way.

Check the ring gaps by putting the bare rings about an inch down into the bore, and measuring the gap with a feeler gauge. You want around .015" to .016" gap in the rings. If you have to file them, use a hard file and be careful to not snap them, and file them nice and square.
Put a little oil on that piston skirt when you install it into the bore.

Just checking.
I always recommend checking everything like that before installing, just in case you might catch some error.

[dogbone]

I purchased  this at  itchcocks, in merry ole  England. The pound was soo low, it was  $100.00 less even with the airfreight.
This is the 2nd piston, the first one toasted, I believe the wrist pin clearance was too close,and froze (only a theory), but there were heat marks.  It only lasted 800 mi.
I had the clearance at .007, thinking this was ample, maybe not.
The new unit  is pre clearenc-ed  at .006, the piston has a much shorter skirt. I will blend in the valve flycuts, I have Kibblewhite valves, they are slightly larger than OEM, and there are too many sharp edges.
I have a ring gap grinder, but the rings are in spec.
Thanks for the reply's,  always accurate on this forum
My main concern was the expansion rate of the alloy jug.

[ace.cafe]

Regarding the alloy jug, in the tests that I have seen on expansion, it appeared that the expansion was very similar to the iron barrel. It just cools better.

The analysis attributed this to the fact that while the barrel may be alloy, the liner where the piston rides is still iron. And that seems to be what sets the expansion characteristics as far as the piston is concerned.
So, as far as we could tell in our tests, the critical expansion characteristics are determined by the iron liner, and the alloy just improves the thermal transfer rate of the heat out of the barrel.

Please post a picture of that new piston, if you'd be so kind.
I'd like to see a comparison photo which shows the differences from your previous Accralite forged piston.
Thanks!

BTW, regarding head torque, I have been using 22 ft/lbs instead, which is a little lower, and it's been working out fine. I actually think you could go down to around 20 ft/lbs and still be just fine. I may try 20 next time I have the head off. It's easier on the studs and on the threads in the engine cases where the studs thread-in. When the Indians changed to metric threads, they had less grip in the alloy threads then, and the torque figures were never adjusted to suit the new metric thread. Those things are known to strip out. I think a 10%-15%  lower torque on those studs is fine, FWIW.