Don Terrill’s Speed-Talk

Hello everyone, I'd like to know who to talk to get some top guided piston pin spacers. Who makes these? I'd like to get some quotes for my engine build. Thanks!

cutta wrote: ↑Wed Jun 17, 2020 3:20 pm Hello everyone, I'd like to know who to talk to get some top guided piston pin spacers. Who makes these? I'd like to get some quotes for my engine build. Thanks!

Are you asking for pin buttons?
teflon/aluminum?
application
pin size
oil support built in?

No he's looking for pin boss spacers to go to "piston guided" rods. Because of the custom nature ( careful measurements MUST be taken ( pin boss span on the piston , rod width and "offset" if any) they are usually made by the engine builder. They also have to be "snug" on the pin or inertia will destroy them. Inexpensive used "cup" rods can end up expensive to use.

piston guy wrote: ↑Wed Jun 17, 2020 5:57 pm No he's looking for pin boss spacers to go to "piston guided" rods. Because of the custom nature ( careful measurements MUST be taken ( pin boss span on the piston , rod width and "offset" if any) they are usually made by the engine builder. They also have to be "snug" on the pin or inertia will destroy them. Inexpensive used "cup" rods can end up expensive to use.

Oh, i always used the right piston for the right rod.
that was what my other thought was. bushings between the rod and piston.

couldnt tell from his wording what he wanted really

Here's a random idea I ran across. A local shadetree, who's not entirely without experience, says he just takes spirolox, pulls them out like springs and puts them between the piston and rod. He's built several that way and never had a comeback.

What say the experts here?

cutta wrote: ↑Wed Jun 17, 2020 3:20 pm Hello everyone, I'd like to know who to talk to get some top guided piston pin spacers. Who makes these? I'd like to get some quotes for my engine build. Thanks!

You can use aluminum or bronze. Any decent tool and die shop can make you some, we have made our own here from Ampco 45 bronze.

You can also try Precision Performance Products in Arden NC. If you are having pistons made for your application, your piston manufacturer should be able to make the spacers.

Make sure the inside of your pin bosses are machined. If they are "as forged", they will have a couple of degrees of forging draft.

PackardV8 wrote: ↑Wed Jun 17, 2020 7:46 pm Here's a random idea I ran across. A local shadetree, who's not entirely without experience, says he just takes spirolox, pulls them out like springs and puts them between the piston and rod. He's built several that way and never had a comeback.

What say the experts here?

Just a gut feeling, but I suspect that even minute angular misalignment of the small ends might result in very substantial side loads that could flatten the 'springs' and leave the rod skewed and the bearing unevenly loaded.

(If I'm wrong though, it would be a great idea!)

Thanks for the replies

I have never used or worked on an engine made with guided pin spacers. I never understood the reason or advantage for using them. Could some of the high end engine builders explain to me why they are sometimes used?

Friction reduction from no contact between rod & crank cheek & less bearing width.
Reduced big end weight, reduced counterweight weight.
Less resistance to oil flow through bearings to turn over the oil in the interface faster.
Slightly reduced windage from narrower big ends.
Small gains, but every small gain added together makes a decent gain.

I've just turned up the spacers from alloy on the lathe, leaving them a few thou oversize & lapping for fit by hand on a flat plate.

You must have forced pin oiling, splash lube of the pins is drastically reduced.

PackardV8 wrote: ↑Wed Jun 17, 2020 7:46 pm Here's a random idea I ran across. A local shadetree, who's not entirely without experience, says he just takes spirolox, pulls them out like springs and puts them between the piston and rod. He's built several that way and never had a comeback.

What say the experts here?

A very bad idea. I am surprised he hasn't seen a failure , but application could be the reason he hasn't.

cutta wrote: ↑Wed Jun 17, 2020 3:20 pm Hello everyone, I'd like to know who to talk to get some top guided piston pin spacers. Who makes these? I'd like to get some quotes for my engine build. Thanks!

Engine builders who do that for a living, make their own.

rebelrouser wrote: ↑Thu Jun 18, 2020 8:57 am I have never used or worked on an engine made with guided pin spacers. I never understood the reason or advantage for using them. Could some of the high end engine builders explain to me why they are sometimes used?

Often the forging has too wide pin boss span for the rod,depending on which forging and which rod obviously
I have run into this several times
If thats the case,i just order the pistons with machined pin boss and make spacers myself,usually from aluminium
0.10-0.20mm is what i have used for clearance,but it is really not that critical
Never had any issues

piston guy wrote: ↑Thu Jun 18, 2020 12:28 pm

PackardV8 wrote: ↑Wed Jun 17, 2020 7:46 pm Here's a random idea I ran across. A local shadetree, who's not entirely without experience, says he just takes spirolox, pulls them out like springs and puts them between the piston and rod. He's built several that way and never had a comeback.

What say the experts here?

A very bad idea. I am surprised he hasn't seen a failure , but application could be the reason he hasn't.

Agree it sounds a bit suspect; what would you expect the failure mode to be?

The lock "fragmenting" or inertia making it "saw" through the pin itself. Neither of which is good.