Don Terrill’s Speed-Talk

Hi guys,
A BBC, Merlin block AFR 335 heads with 12.6 comp on 100 gas, endurance engine in a ski race boat towing 2 skiers @ 7100rpm for 60 - 80 miles per race.
Cam driven waterpump broke the 20 cent keyway & engine got hot enough to shit the commetic gasket & torch the cylinder head & even started to discolor the block deck faces on both sides at the back end.
Upon disassembly, apart from the head,every thing doesn't look as bad as expected.
Pistons look OK & measure up OK but my question is if things got so hot is there a chance of pistons anealing or something & becoming unsafe to re-use.Reliability is everything.If i can't get a positive answer then we will have to buy another custom set but just don't want to throw money away as these pistons were new & this happened on their fist race after a freshen up last weekend
Question to Tony Mamo if he's about. Any advice on welding up the head to re-use for our application or do we ditch it in favour for a new one as it torched the hole back corner exhaust side 2 inches long x 3/8 deep
Thanks

You could ask the piston mfgr. what the stock hardness is, and how soft is too soft, then take a couple of Rockwell readings in the middle of the domes. Or, if the undersides of the domes have thick black carbon buildup, they are pretty well toasted.

Visual inspection should be enough. If there is no melting on top, no four corner scuffing, no blackening under the crown, the ring grooves are o..k. and rings fit freely, the pistons measure properly, they will be o.k.

Keith, all the pistons look good, no scuffing on skirts, rings all free, a couple of pistons have slight tan color under the domes in a small area.Couple of pins also have discolored only slightly.

mmmitch588 wrote:Keith, all the pistons look good, no scuffing on skirts, rings all free, a couple of pistons have slight tan color under the domes in a small area.Couple of pins also have discolored only slightly.

I see why you are wondering. You were getting close.

I think I would use again, but have a couple questions on the discolored pins.

What color are the pins? Were they coated? Are they free in the pin bores? Do you think it's just stain from hot oil? Amber patina / varnish or are they black and blue?

You have to be most concerned with tool steel (pins) when it becomes a dull color. Shiny dark blue isn't death for that material.

JE can test your pistons if you don't have access to a Rockwell testing machine.

Pins have colored a straw color around the small end & have changed to a light blue at the end faces.( i havent dissasembled them yet ) they are JE 52C pins constructed from there 52100 high carbon bearing steel & through hardened.
We are running an Edelbrock 2R tunnel ram & I noticed that it's the centre 4 pistons that have discolored the pins only.I previously noticed this with the old pistons so I went up on jet sizes in the centre 4. ie: primary & secondary on both carbs on one side only to richen the centre only.I think it helped but maybe not enough. I went up 3 sizes.Can manifold distribution be so bad?

All JE pistons we have Rockwell tested start out from 75 to 82 R B scale ,we keep them in service down to 50 R B ,under 50 they go to scrap pile . Rockwell testing pistons and heads helps in determining engine condition ,tune up and keeps our customers honest.

Big Speed wrote:All JE pistons we have Rockwell tested start out from 75 to 82 R B scale ,we keep them in service down to 50 R B ,under 50 they go to scrap pile . Rockwell testing pistons and heads helps in determining engine condition ,tune up and keeps our customers honest.

Agreed. Hardness testing is the only way to determine the servicability of a used piston. All aluminum alloys lose a considerable amount of tensile strength once they have become hot. The hot strength curve drops like a rock and it doesn't take a whole lot of heat, 350-450F.

If in doubt, can you walk back home?

David Redszus wrote: ↑Mon Feb 18, 2008 10:19 pm
If in doubt, can you walk back home?

That's a good point - at least in an airplane you can be confident of making it back to the ground...

In spite of the 60-80 mile pounding on skis visual I wonder if you have a plan to monitor the coolant in order to avoid the same situation.

AA Performance wrote: ↑Sat Feb 16, 2008 11:38 pm Keith, all the pistons look good, no scuffing on skirts, rings all free, a couple of pistons have slight tan color under the domes in a small area.Couple of pins also have discolored only slightly.

That is enough heat discoloration to lose 30+ points on hardness. The first color change is to a faint blue and not a concern. Next is a "rainboe" coloration and would be marginal. After that you get tan , brown , and black. Those show too much heat and should be scrapped. THE one exception is "some" oils "stain" pistons that have not overheated. JE used to Rockwell test use pistons for free. I'm not sure if they still do.

Keep in mind that a welded head can affect the head gasket seal. A head gasket regardless of the design can deform or embed into the soft welded area of the head reducing the sealing stress in that area. The reduced gasket loading can result in combustion leakage and another failure.

I would not chance it...put all that stuff in a crate and send it to me for proper disposal.
If the pistons look fine, probably a good chance they are fine. Oil is what cools them, if they didn't get hot enough to burn the oil and get tight in the bores to scuff the skirts, I would have no issue putting them back in.

Everyone does know this a 12 year old post right?

Tom