Just got my block back from the machine shop today after being bored .030 over.
Installed the crank from my Powerhouse 383 kit.
It fit really well. Only need a small amount of grinding on the oil pan rail near the oil filter to clear the counterweights. Cool..

I installed the first piston (#8 cyl) and discovered the counterweight is hitting the piston skirt.
WTF??

I expected some possible issues with the rods clearing the block and cam, but didn't think crank-piston clearance would be an issue. I purchased the kit as a balanced assy and I really don't want to grind on any of the rotating assy.

I couldn't find a notch on the pistons to ref fwd with, but tried the piston both ways and had the same problem. Tried flipping the rod over too, but that was no help.
The crank is a brand new 383 stroker.
Pistons are the 9.0 to 1 (w/64 cc heads) hypers.
The rods are the CR3's with ARP bolts.
It all came as a kit, so I wasn't expecting these kinds of problems.

Any ideas?

 

umm well my uncle had the same problem and so i went to the machine shop to ask them what was wrong, they said they couldnt tell me unless i brought in the block and everything along, but by time i got back my uncle did things his way. he took a saw and file and files a lil off the piston skirts, at first i thought oh no u idiot but he said if it blows up he would just go buy a new crate engine, so the day came and we fired it up and it ran strong. after we got it broke in we made many 6,000+ rpm launches with it and it still runs just fine, but i wouldnt recomend doing this cuz maybe we just got lucky and would hate it if your motor came apart. i would call up the ppl where u ordered your kit from and ask them what the hell is going on

 

I sent them an email abt an hour ago. Probably won't get a reply till Monday.
Just wanted to see if anyone had any ideas abt what I might be doing wrong.

 

Oh yeah,
When I tore the eng down (it was knocking), I found all the pistons had pieces of their skirts broken off. I assumed it was from the prev owner over-revving it. Now I'm using a different crank, rods and pistons and having crank-piston clearance problems. humm..

 

e-mail me, I'll explain what the problem is. It's familiar to anyone with a bunch of 400 experience which evidently your previous owner, uncle, and shop don't have.

 

When I built my stroker I had to have the piston skirts shaved, but I didn't buy my rotating assembly as a kit. I don't see why you would have these problems with a kit.....definately wait to hear back from the company. Maybe they sent you the wrong pistons?? If you do have to cut the skirts have a maching shop do it so they can rebalance the rotating assembly.

 

yes have them rebalance if u do have them machined. You c my uncle builds motors for race cars and it was his own engine for his car and just needed it to last for a few more races. he was on a budget and didnt have time to fool around so he just took matters into his own hands. Me, i would have never done that but i fiqured what the hell its not my car.

 

I thought you could buy special short skirt pistons for strokers ?

...and hell no I wouldn't start choping up my own pistons to get them to fit. One needs patience on the assembly or the engine won't see 500 miles.

Ron

 

The crank has nothing to do with it. What length are the con rods? Are the pistons designed for that length of rod?

The old way of doing is was with 400 con rods and standard 350 pistons. If you want to use the longer 350's rods then special stroker pistons are needed. If you mix and match any of the parts then you'll have problems.

 

Everything came in a 383 stroker kit from Powerhouse.
It's supposed to all work together.
I did upgrade from 5.7 CR1 rods to 5.7 CR3 rods/ARP fasteners.
I also upgraded to hyper-type pistons. Maybe that's where the problem started.

 

Maybe they packaged it on Monday training the new guy. They make short skirt pistons just for these kits, and always with 6" rods. Sounds like it might be one of those fluke deals-how's your luck in the past with mail order?

 

OK I feel better now, it's morning...

Think about the internal dimensions of an engine for a minute. All stock-block SBC motors have a deck height of 9.025", ± a few thousandths. That distance is from crank centerline to the deck. So: the sum of ½ the stroke (center of main journal to center of rod journal), plus the rod length (center of big end to center of small end), plus the piston pin height (center of pin bore to top surface of piston), plus the deck clearance, equals 9.025".

The factory was unwilling to compromise the ring package on the 400 piston when they designed it. So, the pin height is the same as the 350 pin height. The deck clearance is of course the same as a 350 as well, at around .025". the stroke is longer, 3.75" vs. 3.48". The only thing left that they could change to fit this inside the block was the rod length. So, 3.75" - 3.48" = .27"; half of that is .135"; 350 rod length is 5.7"; so 400 rod length is 5.7" - .135", or 5.565". Make sense so far?

Since the rods are farther from the crank centerline, i.e. the journal is farther offset thereby giving the longer stroke, the counterweights have to be larger in a 400 than a 350. Now think about the counterweight for a minute: it's exactly opposite the rod journal on the crank, that is, when the piston is all the way down in the bore, the counterweight is all the way "up". But, remember that the 400 rod is shorter; so there isn't enough room under the piston for the extra counterweight metal required. As a result, where 350 cranks have circular counterweights, stock 400 cranks have their counterweights shaved off at the corners, at a weird angle. You can spot a 400 crank from 100 yards away if you know what to look at because of this. And, since the counterweights are unable to be big enough, they had to externally balance the 400.

So: If you are willing to accept a less than perfect (for longevity) ring package, using either thinner rings or closer ring spacing or both, and if you are willing to allow the piston pin to intrude into the oil ring's land, then you can use a longer rod in a 400. This allows you to use an internally balanced crank, because now there can be enough room for the counterweight. Remember, the rule is, short rods require external balance because the pistons will hit the crank otherwise; long rods allow internal balance because there's space to fit the counterweight.

Like Stephen said, stock 350 pistons will work to make a 383 with a stock externally balanced 400 crank and stock 400 rods. That's how all of us have been building them for all these years before these "kits" became available. However, no stock pistons of any kind will work with an internally balanced 400 crank, unless it's cut to stock counterweight dimensions and plugged with Mallory metal ($$$$$$$$).

You have an internally balanced crank, and pistons for a motor with longer rods than yours. Probably you have the pistons for a 6" rod motor. The pistons for a 6" rod motor can have longer skirts than the ones for 5.7" or 5.85" or stock 5.565" rods, unlike what the prior post said.

Get them to send you the right pistons.

 

Well I got a hold of Powerhouse today. They said they have seen this issue before and it's really not an issue, "just get your hand grinder and shave a little off the counterweight", he says.
They said the amount I needed to remove wouldn't make any noticeable difference with the crank balance.
It is just barely hitting, so maybe he's right. Just seems kinda wierd though.

 

umm... just whack away at the counter weight? Something sound wrong here?

 

if i did anything i'd remove metal off the piston. i'd chuck it in a lathe and then you would be sure of removing the same off each piston.

 

The spot on the piston that is touching is on the side of the skirt extension (not sure if that's the correct name for it; it's the tang that sticks down on both sides of the piston).

It's only hitting at one spot on the counterweight. About 1-1.5" from the end of counterweight.
(A pic would help a lot here.)

It's an area where there is a radius transition. I'm sorta having to round off a slight corner. The grind area is abt 1/2" long, by 1/8" wide and I'm grinding abt .060" deep.
Very little material is actually being removed.

I'm starting on the second cyl now and it looks like it will need the same treatment. Humm,,, if all the counterweights need the same treatment, it may even itself out, or at least be pretty close.
This eng will never see anything above 5500 RPM so I'm thinking it will be OK as is.

 

Well, now that you're grinding on the pistons it's a mute point with the supplier but just so you don't feel too lonely. . .

Last year I bought a Scat 3.75 one piece rear seal crank, Eagle 5.7 bushed rods and L2491F TRW pistons. Not as a kit but the pistons were specifically for a 5.7 rod stroker engine. When the machine shop mocked up the engine to zero deck the block the piston pin lands probably missed clearing the crank throws by an estimated .050 or so. After double checking the rod part numbers and crank measurements I was told by Scat that the TRW's seem to have this problem, buy the SRP's and it would clear. Man, was I confused! The TRW's were advertised for this combination! Anyway, www.partscavengers.com gladly refunded my money on the TRW's and I bough SRP's and everything cleared perfectly.

I sure was one confuseled sucker for a few day though!

I about drove Scat nuts for a couple of day wondering if maybe I'd bought an internal balanced crank with bigger throws or something. After them taking measurements and calling me back I found the crank to be what it was supposed to be, rods were right so... that left the pistons.

So... anyways... I feel your pain! Good luck and let us know how it turns out.

 

repeat, sorry can't delete...

 

ZZ28ZZ - If you can, to get in writing from Powerhouse that it is ok to grind the crank.

Only pistons 1, 2, 7, and 8 will be affected by the larger throw of the counterweight.

3, 4, 5, and 6 really don't have a counterweight.

Check for rod bolt - to - block clearance.

Best to have a small base circle camshaft. Put playdough on top of the rod bolts, rotate engine and make sure you have at least 0.10" clearance between the top of the rod bolts and cam lobes.

Rod bolts of either cly 7 or 8 may bump into the oil pan.

When adding a longer stroke crank, CHECK EVERYTHING ----TWICE!!!!!

 

Finished the clearance work tonight.
Still have to check cam clearance when I get it in there.

Had to grind on the counterweights for 1,2,7,and 8 cyls like a73camaro stated.
Didin't grind on any of the pistons per Powerhouses' recommendation.

Oil pan rails all cleared the rod bolts but not by enough. I now have .050 to .078" clearance on everything (except cam).

The rod bolts are ARP's. The bolt heads are specially shaped.
There's not much left to grind.
Hopefully they'll all clear, but I'll check them when I get the cam.

.050-.080" clearance was mentioned in an earlier post as being ok for the rod to oil pan rail clearance.

With the pistons being aluminum, and having a higher expansion rate, I'm now wondering if .050 - .080" will be enough for the piston-crank clearance.