Bought a 66 tripower, it came with a 400, what do I do with it?
 

Like the title says, I bought a 66 tripower setup. The tripower came with a 400.

I'm gonna post a million questions about the tripower in the tripower tech area... For now I have a question about the 400 that came with the tripower.

The block is a 9790071, it date codes to 1968 production, and is a YE code, so it was originally a 340 hp engine. According to Wallace Racing's site it should have 16 heads, but it has 15 heads which is kind of a bummer.

I got it home and of course got curious and started taking the 400 apart. It looks like it was barely broken in. It's 0.040" over, but there is no cylinder ridge, there is visible cross hatching, and a quick pass with my bore gauge shows no real taper.

It had a Crower M-280-H camshaft, with 3 broken lifters and a couple others that look suspicious. I'm wondering if the lift of the Crower cam was incompatible with the retainer to guide clearance in the heads? Either way the lifters and cam are going in the scrap pile.

The disappointing thing is that they used cheap 8 valve relief pistons.

I have a magnetic bridge coming so I can check how far down in the hole the cheapo pistons are. Once I do that I'll finish tearing it down and check the rod and main bearings.

So, dumb question... If all the bores look ok after teardown, can I install some decent pistons without boring it out to 0.060" over? I know the piston to cylinder wall clearance requirement is different for cast, hypereutectic, and forged pistons and also depends on what alloy was used to make them. Can I likely find a decent hypereutectic or forged piston, hang them on rods, hone the bores just enough to freshen up the cross hatching and run it, or am I asking for trouble? I wiped the bores with some carb cleaner and a rag. There is some discoloration at the top ridge area, but you can't feel it and certainly can't catch a fingernail on it. The bores are all measuring 4.1615 to 4.1652 on my bore gauge (that I set as best I could with a 4-5" micrometer, after checking it with a 4" standard pin). IIRC 0.060" is the last stop for a Pontiac 400 and that's with sonic testing recommended, so I hate to bore it if I don't absolutely have to...


https://forums.maxperformanceinc.com...ictureid=14625

Does anybody know what brand this piston is? It's marked as being 0.040" over, but does anyone recognize the other mark?

https://forums.maxperformanceinc.com...ictureid=14626

YES - for a basic rebuild, it should be fine.

_ou can check the depth of the pistons with a straight edge and feeler gauges...

You have cast pistons so the clearance is tight. You could run some forged pistons that need .004 clearance and ridged hone it.
Or this. There are rings available for FE fords in 4.170 bore size. So that means one could have some custom Pontiac pistons made that are .010 larger than you have right now. Then ridged hone it with tq plate to fit your new pistons.
Then buy a decent set of forged rods. Ones with PMD journal size were harder to find but it can be done.

Have your machine shop measure the current bores, and then with the shop's blessing buy the set of .040" over forged pistons and have the machine shop measure the new pistons when they come in and hone the walls to the proper size.

Keep in mind that custom pistons can be any diameter (as long as the proper ring set is available), so .040", .045", .050", etc... can be purchased. Would be a shame to hog the cylinders out more than needed.

What do you mean by broken lifters?

If physically broken then I would be more concerned about lifter bore clearance possibly.

If you place a lifter that has not busted into one of those bores do you find any more side clearance?

Too much and a flat tapped lift will just wobble and and spin like it needs to .

Badger pistons

Yeah, I got my head out of my rear end and remembered that I have a dial indicator and a magnetic base. I rigged it up, found TDC, and measured the pistons with a depth mic... They are 0.034" down in the hole! Yeesh...

0.034" plus a .042" gasket is .076 crushed height but unfortunately is right where a Pontiac engine would not be happy as far as the combustion process.

Tom V

And not to mention the much higher chances of pre ignition from all the sharp edges of those 8 valve notches along with the added collection of fall out fuel in those 8 notches .

This fuel either burns too late to make power because it burns in the exh port making for added engine heat, or if it does light off does so in the form once again of engine distroying detonation.

I am of the opinion that Those 8 notch pistons from day one have caused more issues then they solved on average!

Pistons with a overly large dish which worked for both early and late heads which dropped compression a tad more then those 8 notch pistons would have made more power without the bad side effects.

Yeah, I know that pistons 0.034" in the hole won't be good for quench.

I looked at a couple brands of those 8 relief pistons and they all look to have a compression height of 1.700. If I get some 1.720" compression height pistons like these:

https://www.summitracing.com/parts/u...0/make/pontiac

That would theoretically put me 0.014" in the hole. Combine that with a 0.040" gasket and I'm at 0.054" quench height. Still not great, but definitely better.

I know you want 0.040" or so... How bad is 0.054"? I know a lot of stock engines were worse than that.

this is what I would do now if it where me and I was not planing to use the car until next season and I had or will have a extra 700 bucks in the motor building budget.

I would get new 4 notch or better yet 2 notch Pistons and new rings and then get the rotating Assy rebalanced.

That's more or less the plan. I was going to spring for a set of rods just to be safe. I guess I can always just get a set of Speed-pro 2262-40s, a set of Scat rods, and have the whole mess balanced and ready to go.

There is absolutely no hurry with this engine. It will likely end up in the 67 GTO so that I can move it around without pushing. The numbers matching engine is locked up. But that whole basket case is taking a back seat to other projects for now.

Hey there,

I have this exact some scenario for a 400 I was planning to put in my 62 GMC. What did you end up doing and what parts did you use? I’m trying to keep this a inexpensive as possible.
Thanks

I haven't done anything with it just yet. I had set this motor aside and focus on doing a bunch of work on my truck (fuel lines, brake lines, new front and rear brakes... Getting rusty old bolts off is so much fun). And then I got sick and couldn't do much of anything. I'm finally back on the mend, but I'm catching up on other chores (leaf raking and getting the house ready for winter).

Too many irons in the fire!