Don Terrill’s Speed-Talk

dear speedtalkers,

I am building a datsun a15 engine for a fellows b210. It is a 1500cc 4 cylinder and with the piston I will be using and the block 0 decked, we will be right up around 10:6:1 compression ratio. The engine will be spun to around 8200 rpm.

Currently, there are no .040" pistons available. A few sellers on ebay realize this and are selling these cast, 040's they have in stock for around 1k. Ring packs in the 500 dollar range : ( These pistons were going for under 100 bucks about 4 weeks ago, but they are all gone at this time (nissan ga16de)

what is available however, and on my bench at this time, is a 2 groove piston. One compression ring, and one oil control pack. Is this going to be an issue at these RPM's and cylinder pressures?

some modern 4 stroke motorcycle engines use 2 groove pistons, are high compression and spin 14k rpm (honda) food for thought. did I just answer my own question?

please advise speedtalk!

Contact some of the custom piston manufacturers, the cost of a custom set these days for a four is not prohibitive.
Not only that, a lot of manufacturers have already made the same or similar and could have architecture already on file [although not in a catalogue]. If you go a custom set you get to dictated the ring pack as well.

Cheers.

guy, if it was boosted or juiced it would be getting forged bits.

come back in 5 minutes and give this one another go. I was hoping someone from Australia would pop in here cause for the most part you guys are wicked smart and build some killer shit.

All pistons have a single compression ring. The second ring is for oil control.

Not enough rpm to make a single comp ring work I suspect.
A15 just takes a plain flat top from memory, unless you get silly with the cam, so a custom should be dead simple.

I may have an oval port A14 head somewhere I think.

hi knight. the a15 uses a heavy dished "bathtub" style piston top.

the ga16de pistons Im using have a smooth even concentric dish to them.

Im going to wing it guy and keep my fingers crossed, but your thinking at lower RPM's that one ring isn't going to cut it huh?

https://www.ebay.com/itm/SIZE-040-Pisto ... SwCHBbGvPZ

these are the pistons Id like to use. 3-4 weeks ago the price tag was about a buck 'n a quarter.

I have called everywhere and can't seem to get my hands on a set of 3 groove pistons...


edit: found a 3 ring set on ebay with rings for around a bill on the way. very happy right now.

If burning a "little" bit of oil between changes does not worry you.......... then not a darn thing to be afraid of.
Aeries used to do a lot of them with only two rings, and mostly they worked great.


Far as the two ring pistons.... higher cylinder pressure and/or some crankcase vac, would be a GOOD thing probably.
Second rings are usually sharp edged and angled, tapered, so they have narrower point of contact with the cylinder wall.
So LESS outward pressure is needed to make them effectively scrape the oil down instead of "hydro-planing".

Two ring piston I'd expect good compression seal, and probably no real oil burning when you have your foot in it,
but maybe a little puff of smoke at each shift, or when cruising at very light throttle, is where you might notice your missing a few rings.

Fyi honda uses a torsional ring to push the lower edge out on the down stroke for squeegie action.

Kinda closes up the axial clearance which will slow pressurization of the ring

I have done 3 Kawasaki Z900/1000 big bore engines using 2 ring pistons. Worked well in the applications 2 were street bikes. No oil issues, no compression issues.
But smaller bore than you're looking at.

bentvalves wrote: ↑Thu Jan 16, 2020 10:19 pm https://www.ebay.com/itm/SIZE-040-Pisto ... SwCHBbGvPZ

these are the pistons Id like to use. 3-4 weeks ago the price tag was about a buck 'n a quarter.

I have called everywhere and can't seem to get my hands on a set of 3 groove pistons...


edit: found a 3 ring set on ebay with rings for around a bill on the way. very happy right now.

They can be made for right at 750.00

so I am considering blocking the thrust side oil squirt hole in the big end of the connecting rod to give this 2 groove piston a fighting chance at actually controlling oil on the bore.

think I'm askin' for trouble going this route fellers?

Yes.

Call Total Seal .

Don't block the oil.
Do call total seal and see if they have a ring type is best for it