New Hampshire CMP Barn 2011- 2012 HUP Overhaul

[Phil Waterman]

Hi Rob

Yes, I looked at Jim Carter but could not find the dimensions in their catalog to confirm the correct ones, which was one of the reasons I did the little drawing to send off to them and Obsolete Chev to see if they matched.

A point in passing, the pins that had brass/bronze bushings it was the bushings that were worn, on the rear where they used steel bushings it was the pins that got worn. As bushings are easier to find and pins are harder to find, I'm using bronze all the way around.

Cheers Phil

[Mike K]

Phil

Can I ask you: What's your opinion on the cast iron versus alloy pistons ?

I bought a set of aftermarket alloy 216 pistons years ago. I weighed them against the original cast iron set - the weight was only 25% less than the cast iron set.I was somewhat dissapointed .

MIKE

[Bob Carriere]

Hi Mike

A 25 % reduction in the reciprocating mass is significant particualrly at higher RPM.... but doubt you would notice a difference in your 216.

In racing circles anything you can do to reduce the weight of a metal mass that has to reverse direction of travel is important. Theoretically it should allow the engine to gain its RPM faster, rev faster while not iducing as much strian on the rods, bearings, crank, etc. and easier to pickup revs in gear down situation. Reduction in weight should make for a smoother engine and longer life. The special alloy piston may be more stable at various temperature..... expansion/shrink rate from cold to hot maybe better controlled....potentially quieter on a cold start. Piston skirts may cause less oval wear on bottom of cylinders.

But in a CMP at 40 mph 2800rpm... you should not feel much difference.

If I was rebuilding a 216 I would take advantage of the latest technology and buy the modern alloy version rather than hunt for NOS old stock.

My 0.05 worth........... Phil what are you using....?

Bob

[Phil Waterman]

Hi Mike and Bob

I've used both, Bob is correct that at the RPMs the 216, 235 or 261 are turning it probably is not a noticeable or even measurable difference. Equal weight however is more important the entire piston,rings,and rod assembly should be as nearly perfectly matched as possible.

Having said that I taken apart running 216s to discover that they were a total mix and match of parts. One engine in particular had several different types of valves, some of the pistons were over sized some weren't thing must have been assembled out of the scrap pile. But it ran fine. I got it as a spare engine its history is unknown. Right now it is in the Pattern 12 C60L seems to run fine. When the HUP is done the Pat 12 it will get the 235.

Now the 235 came out of a junk yard truck, with serious valve train problems due to an oil line failure of the line to the rocker arms. But it had cast iron pistons which the rebuild shop magnifluxed found them to be OK and reused them along with rods cylinders just needed honing.

The 261 they bored out .060 so it need new pistons and they replaced them with aluminum.

I don't think I would reuse any old cast iron pistons or even NOS with out have them checked for cracks. It's just two messy when they fail.

The only piston I have ever had catastrophically fail was on a J-3000 Jeep with a 350 Buick engine. The number one piston disappeared inside the engine at full throttle plowing snow. After a very load bang there was total silence, opened the hood the wrist pin and half a connecting rod was laying on one frame rail. On the other frame rail was a 4" chunk of the connecting rod. When we did the autopsy of the engine we could not find the piston all we found were lots of little bits of aluminum. Apparent cause piston striking a valve.

Next week the 216 out of the HUP comes apart to decide how much of an overhaul it will need. I suspect that if the pistons need to be replaced I will go with the aluminum as they seem to be easier to get from a known source.

Cheers Phil

[Bob Carriere]

Hi Phil

when I had my 261 rebuilt I read and it was confirmed by the engine shop manager that Chev 6 are seldom "balanced" as they are deemed "inherintly" balanced by the very design of the engine crank..... which apparently is not so for a V8.

In any event, for an extra $300 they did balance the 261 ... the focus was apparently getting each piston assembly....new piston, rings, rods, wrist pin, etc. within on gram of one another......

Doubt I will ever spin the engine fast enough to take full advantage of the process .... just hoping that it would make it smoother running even at lower speed.

Bob

[Grant Bowker]

Originally Posted by Mike Kelly

.....the weight was only 25% less than the cast iron set. I was somewhat dissapointed.

The way I look at it, if I could cut 25% off my weight while jumping up and down as often as the pistons, I think I would notice the difference. I know my knees and muscles would love me.