Trying to get STI pistons to work....

douglas vincent · Post by **douglas vincent** » Thu Mar 15, 2007 1:25 am

The STI pistons are made so that the area that the top of the rod fits into gets narrow, so the tops of the rods must be angled to fit.

gto7419 · Post by **gto7419** » Thu Mar 15, 2007 1:33 am

douglas vincent wrote:The STI pistons are made so that the area that the top of the rod fits into gets narrow, so the tops of the rods must be angled to fit.

I was wondering why you were milling at an angle on a rotary table....

douglas vincent · Post by **douglas vincent** » Thu Mar 15, 2007 3:45 am

OK, I commited.

Its going together with the HUGE deck to piston gap......

I DID pin the cylinders to the block though with brass 5/16" pins.....

And the rods are connected to the crank, I would have it done, but I forgot to by block goo, be done tomorrow morning.

azn2nr · Post by **azn2nr** » Thu Mar 15, 2007 4:01 am

im so confused as to what your doing.

first off phase2 rods are 52mm crank journal and phase 1 is 48mm so you have to have mathching crank and rod bearing sizes. also 2.5 is the shortest rod see stroker application??

so yeah im confused.

gto7419 · Post by **gto7419** » Thu Mar 15, 2007 4:02 am

[quote="douglas vincent"]
I DID pin the cylinders to the block though with brass 5/16" pins.....
[quote]

Do you have any pictures of this? Im wondering how its done.

douglas vincent · Post by **douglas vincent** » Thu Mar 15, 2007 4:21 am

Its my God Given Duty to confuse asian people.

PhyrraM · Post by **PhyrraM** » Thu Mar 15, 2007 5:16 am

Pretty sure that 2.5 rods are the longest ones. The piston pin location is raised closer to the crown to compensate.

A 2.5 piston has the pin almost in the oil control ring if I'm not mistaken.

douglas vincent · Post by **douglas vincent** » Thu Mar 15, 2007 7:20 am

I will have some pics tommorrow.

Post by **Legacy777** » Thu Mar 15, 2007 5:52 pm

douglas vincent wrote:Its my God Given Duty to confuse asian people.

quote worthy

azn2nr · Post by **azn2nr** » Thu Mar 15, 2007 11:28 pm

well that didnt help.

and stroker = shorter.

douglas vincent · Post by **douglas vincent** » Sat Mar 17, 2007 4:46 am

206er · Post by **206er** » Sat Mar 17, 2007 5:59 am

cylinder pinning is sweet!
did you pre drill or is it a really tight press fit? only worry with really tight it that its possibly doing something to the bore roundness or something. i think I can see some pre drilling but not sure.
how about adding a couple more, overkill?

gto7419 · Post by **gto7419** » Sat Mar 17, 2007 6:02 am

Im curious as to how those are installed - Do you mill out a hair under 5/16 bang the pins in and mill them flush? What about thermal expansion? Is pinning the cylinders common?

douglas vincent · Post by **douglas vincent** » Sat Mar 17, 2007 4:55 pm

I used a hand drill and a 5/16th REAMER. A reamer gives a much better round hole and is "easier" to drill with.

Then I used my little lathe and turned 3/8" rods of brass down to individually fit each pin. Then I tapped them down.

The block may or may not be out of round now, but I dont really care because this is a test build just to see if it works. If I have to do another one, then I will take the block to a machine shop and have it bored.

Post by **Legacy777** » Mon Mar 19, 2007 5:30 pm

What about thermal expansion?

I'd have to look and see what the differences between brass & aluminum are, but if they are reasonably different, then all the work could not do squat, or it could hurt you.

Ideally, you'd want to use a material that has the same thermal coefficient as the block material.

555BCTurbo · Post by **555BCTurbo** » Mon Mar 19, 2007 8:08 pm

Legacy777 wrote:What about thermal expansion?

I'd have to look and see what the differences between brass & aluminum are, but if they are reasonably different, then all the work could not do squat, or it could hurt you.

Ideally, you'd want to use a material that has the same thermal coefficient as the block material.

+1

If I recall correctly, brass has a much lower thermal coefficient than aluminum...

douglas vincent · Post by **douglas vincent** » Mon Mar 19, 2007 8:25 pm

I snub my nose at physics.

206er · Post by **206er** » Mon Mar 19, 2007 8:45 pm

I dont think it will be an issue with such a small surface area. but why not some aluminum rod doug? it's quite cheap.
also there's maybe a possibility of some kind of galvanic corrosion but perhaps not.

Post by **Legacy777** » Tue Mar 20, 2007 6:51 pm

Surface area really doesn't matter, the thickness of the material does.

I looked in one of my books and here's what they have for the average coefficients of linear thermal expansion:

Aluminum Alloy = 12.8 x 10^-6 (1/(deg F))
Brass = 10.0 x 10^-6 (1/(deg F))

If you work out the thermal deformation equation for area, you get the following change in area for each material:

Aluminum Alloy = 2.55 x 10^-4 in^2
Brass = 1.99 x 10^-4 in^2

Those are pretty small numbers, and the difference between them is even smaller. However if it were me, I'd still probably do some looking into things....but you'll probably be fine.

evolutionmovement · Post by **evolutionmovement** » Wed Mar 21, 2007 12:57 am

With the way Doug goes through motors electrolytic corrosion won't be an issue.

brando · Post by **brando** » Wed Mar 21, 2007 5:35 am

^^^haha thats so true!

93forestpearl · Post by **93forestpearl** » Wed Apr 11, 2007 6:17 am

updates?

douglas vincent · Post by **douglas vincent** » Wed Apr 11, 2007 4:01 pm

311 hp 354 torque at 23 psi

multiple 12.7 @ 109 mph 1/4 miles!

Runs awesome!

Post by **DLC** » Wed Apr 11, 2007 8:22 pm

You need to update your sig now

skid542 · Post by **skid542** » Thu Apr 12, 2007 12:27 am

Geeze

.

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Trying to get STI pistons to work....