[chiefbigb]

I like Don's approach to the issue. Easily done with the right equipment.

[Jay S]

The squirter’s do not directly spray at the cylinder wall. If you did, your trying to do something different than how a pistons squirter (piston cooler) is meant to operate. The goal is to cool the pistons. The Squirters must hit the underneath side of the piston.

Newer style Diesel pistons have oil cooling passages inside the underneath side of the pistons. The squirters are positioned to hit the port holes for those oil passages for even more piston cooling.

Older types pistons with no cooling port (like a gas engine and most older diesels) just sprayed the bottom of the piston for extra cooling. Long hard pulls it keeps the pistons from expanding, the pistons last longer, less scuffing from less expansion. The oil acts as a heat sink, it is not for lubrication.

[Elarson]

Originally Posted by Elarson

The Boss Bird had scuffed and cracked piston skirts when we were using the recommended piston-to-wall clearance. We tried loosening the clearance (maybe .002" extra?....memory fading) and the problem disappeared.

The Pontiac piston is less massive than a hemi nitro piston so it was growing a lot quicker and binding in the bore.

I'll see if I can find a picture and post.

Edit: don't have pix anymore but the piston is at work in my show-and-tell stash so I can take a picture Monday.
The skirts would get 2 cracks on the side perpendicular to the pin bosses. The pin bosses are heavy and take awhile to heat up. 90 degrees from that, the piston and skirts are thin and heat quicker. So the piston goes oval while it is warming up.

I never could warm up to the idea of piston squirters being necessary since the crank is flinging oil up into the cylinders. But since the OEM's go to the expense on some engines, there must be a benefit. I'm willing to be educated.

Eric

Here's the pix of the piston that got killed by binding in the bore.

To make a nitro engine survive, the thing has to be super loose.
Piston-to-wall has to be pretty sloppy
Mains need .007+ clearance (when you can grab the crank nose with your hand and make it clunk up and down, you're about right)
Valve guides need to be loose so you don't hang a valve and grenade the whole engine
If the exhaust valve heads are distorted a bit and won't seal after a run, it's ok.....they'll straighten up the next time you pour the coals to it.

Eric

[mgarblik]

Originally Posted by Elarson

Here's the pix of the piston that got killed by binding in the bore.

To make a nitro engine survive, the thing has to be super loose.
Piston-to-wall has to be pretty sloppy
Mains need .007+ clearance (when you can grab the crank nose with your hand and make it clunk up and down, you're about right)
Valve guides need to be loose so you don't hang a valve and grenade the whole engine
If the exhaust valve heads are distorted a bit and won't seal after a run, it's ok.....they'll straighten up the next time you pour the coals to it.

Eric

That skirt damage was at .009"-.0095" piston to wall clearance. Problem went away almost entirely at .0115"-.012" The engine will tell you what it wants to be happy. Just have to look and listen to what it says.

[Jack Gifford]

Originally Posted by Tom Vaught

... you want the squirter oil to contact the underside of the piston...

Since I suspect lack of oil retention on my super-smooth cylinders, I want the oil to strike the walls. Due to restrictions on nozzle locations, oil will hit the wall for about half the stroke, and bottom of piston for the other half stroke.
Also... I've decided to remove the blower to get some experience with the engine under less stress. Hopefully learn enough to later run blown.

[Tom Vaught]

Could you explain, Jack, why you wanted a super smooth cylinder bore for your Land Speed/ "Texas Mile" type racing?

Tom V.

[misterp266]

Originally Posted by Tom Vaught

Could you explain, Jack, why you wanted a super smooth cylinder bore for your Land Speed/ "Texas Mile" type racing?

Tom V.

Tom, See OP.

“ (done per Smokey Yunick's "the smoother the better" edict) “

[Jack Gifford]

With Mike's help, design of the squirters is progressing. I've selected some Honda nozzles and machined hollow studs to mount the nozzles through one pan rail of the block. I need to machine an AN-3 male flare onto the exterior ends of the studs, but am having trouble determining the correct flare angle. AN flare fittings are nominal 37 degree, but I need to know the exact angles- I'm quite sure that the male and female flares are not identical angles. Anybody help?

[Elarson]

Jack: I'm looking at my "Parker Tube Fittings Military Specification Handbook".
It shows the male and female ends to BOTH be 37 (+/- 1/2) degree.
If you want to make them slightly different, then you could machine one of them to the high side and one to the low side of the tolerance. But they have no intentional offset.

Eric

[cgeise]

I had micro welding of the rings to the piston in the old turbo car -- coolers may have helped

[Jack Gifford]

Thanks Eric. I guess I was wrong to think that the male/.female angles were slightly different.

[Jack Gifford]

Mike G- to install the nozzles into the assembled engine is challenging! Similar to the situation with chamfering the interior of Boss Bird's oil passages, I had to invent a tool to spot-face the interior side of the nozzle stud holes which are within 3/4" of the crank counterweights (the as-cast block surface needed spot-facing to allow sealing washers to function). I expect to wrap up the installation in the next couple of days.
[Sorry for the poor quality photo of the mirror image]

[mgarblik]

Thanks for the update Jack. So I guess that means the Honda part numbers we came up with for the squirters were correct. It does look pretty tight in there. My Honda guru says in the Honda applications, they have had a few instances where a technician has not aimed the squirters just right. In operation, the counterweights have lightly contacted them and in a few instances, broken them off. This caused an immediate oil pressure loss in the Hondas. So make sure you have enough clearance in there. This is super cool stuff!

[Jack Gifford]

Of course, "next couple of days" became a week! And upon trying to crank it over, the Tilton starter just spun without engaging the flywheel. So... a couple more days spent adapting the solenoid from an older Tilton. S'pose it might work this time??