Crank counterweights hit Pistons in 327 build! [Archive] - Team Camaro Tech

: Crank counterweights hit Pistons in 327 build!

Jan 16th, 07, 06:45 PM
My Crank is hitting my # 3,4,5,6 pistons. I called my shop and told them about the problem. They are going to call me tommorow. I have an Eagle 3.25" stroke forged crank, Eagle 5.7" rods and Speed Pro forged 327 pistons.

Anybody else had something like this happen? I figured since I was going with a stock stroke I would have no problems and this came as a big surprise.

Jan 16th, 07, 09:09 PM
5.7" long rods regardless. They have the wrong pistons in it!!

OR, OR!!

The crank isn't cut to a 327 dia. counterweight dia......................

End of conversation!!

Double check this big-time, imho!!


Jan 16th, 07, 09:23 PM
sure you didn't get a 350 crank on accident?

Larger Dave
Jan 17th, 07, 02:31 AM
Or that the 327 crank didn't call for a 6.0" rod?

Jan 17th, 07, 04:33 AM
Make sure they gave you the right crank. There are two depending on the year. May have the small one with a large block. I believe it was 1967 was the year when it was changed to the larger journal like a 350 crank. I believe that the smaller had more weight inside and called for a smaller ballancer on the front of the block. I think they cut the bottom of the block to accomidate the extra weight. Anyway its worth check first.

Jan 17th, 07, 05:44 AM
Make sure they gave you the right crank. There are two depending on the year.

It's an Eagle crank and according to their catalog they offer one (1) 3.25" stroke crank for the early SBC's. It requires 5.7" or longer rods. Maybe the piston skirts are long. If it was me I'd use a 6.125" rod and a 1.25" or 1.26" CH piston depending on how much deck you've got.

Jan 17th, 07, 05:53 AM
5.7" long rods regardless. They have the wrong pistons in it!!

OR, OR!!

The crank isn't cut to a 327 dia. counterweight dia......................

End of conversation!!

Double check this big-time, imho!!


What pdq67 says.
Been there myself.
In my case a Stroked 384.6 CID, I was origionally using Wiseco ProTru pistons. Switched to SRP pistons and problem was solved. The Crank counter weights were hitting the bottom of the piston boss area on the Wiseco pistons.

Jan 17th, 07, 07:02 AM
I have used those pistons on a awful lot of motors. Do the pistons come up to the correct heigth in the block? Have no clue about the crank having too big of counterweigths I haven't played with that brand but anything can happen.

Jan 17th, 07, 10:49 AM
I have measured everything and the stroke is indeed 3.25 and correct. I think the counterweights were just designed to go with something with a little shorter area under the pins as that is where it hits. How much can be taken off the piston under the pin? We are talking on the order of less than .125" most likely. The other alternative is to take about that much off the backside of the two crank counterweights that are causing the problem if that would even be possible. The issue is that the shape of the two inner counterweights tapers out (gets longer) as you go to the backside of the weight.
From what my shop says the pistons can't have material removed from there since it would weaken it too much. Now to call Eagle and see what they say.

Jan 17th, 07, 11:20 AM
Eagle says to grind off the offending area until I get .060 clearance. I popped in one of my old pistons/ rods and it just barely clears. The piston (TRW forged flat top) has less material in that area than the new ones.

I am going to have my machine shop take the material off on their lathe since I want it done cleanly, then rebalance. Unfortunately they are on a 8 week backlog. I have plenty to do to get the car on the road though so will concentrate on getting the rest done now.

Guess it juse shows you can't trust these parts to fit even for stock configurations.

Jan 17th, 07, 03:03 PM
I have pictures of the problem and the two piston types, if anyone is interested I can email them. I just want this to be a warning to other builders so they can expect that there could be an issue of parts compatibility.

Fred Ficarra
Jan 17th, 07, 05:02 PM
I have pictures of the problem and the two piston types, if anyone is interested I can email them. I just want this to be a warning to other builders so they can expect that there could be an issue of parts compatibility.
Hmmm, sounds like more of a problem with Eagle's parts.

Jan 17th, 07, 06:01 PM
You really need to have a competent Machinist cam-cut your cranks counterweights and then rebalance it AND I will bet a 6-pack to a donut hole that you will need to add heavi-metal after doing so..

It went right over the top of my head when Lunati's Salesman told me to use at least 1/4" longer rods in my 496 b/c I had a good set of truck rods i wanted to use.

And sure enough, I had this problem and if I would have listened to the guy, my big motor would have stock balanced fine after welding up some counterweight holes!!

CAM-CUT here b/c you most definately will need heavi-metal if you cut their complete diameters down by just chucking it up centered!!!

I ended up having Lunati's fixing my f--up and rebalancing it w/ h-m and in the end everything was fine!!


Larger Dave
Jan 17th, 07, 06:46 PM
I agree with Paul (pdq67) in that you will probably have to rebalance the crank anyway, but rather than putting money into heavy metal at $50 bucks a slug, I'd invest that money in a new set of pistons with smaller skirts and less reciprocating weight (like I said a rebalance will be in order anyway). And while your buying new pistons now would be a great time to invest in some longer than stock 5.7" rods; 6.0" is a good start, but I'd go still longer with a 327 (let piston availability and cost be your deciding factor).

Larger Dave

68Lemans blue
Jan 17th, 07, 07:03 PM
Don't mess with the pistons do the chamfer thing and rebalance or send the crank back.,you should not half to ,common stuff stock stroke ,I know I had to chamfer cut the web of my block to get my 6.0 rods to work,as this motor has been together for a couple yrs, so I beleave was close tolerance wise on a couple pistons .050 or so counterwight to pistons,good luck bud , Happy Motoring

Jan 17th, 07, 07:39 PM
You can get Eagle SIR 6.125" rods pretty cheap, and just about everybody has a 1.25" or 1.26" CH piston, it's made for a 350 with 6" rods. We use a similar setup in our road racing 331's.

Jan 17th, 07, 08:30 PM
I have seen this before several times on both Eagle and Scat cranks. The counterweight is just made wrong. I would send it back and get the correct one. The problem with grinding the counterweights to clear is that depending on how much they have to remove, you will now have to add weight to rebalance the crank. This means either welding up previously drilled holes, or adding heavy metal. Neither one is cheap.

Send it back and make them get it correct. If you ask nicely, Eagle will probably even balance it for you for a reasonable price, just send them the bobweight.

By the way, and I just have to throw this out .... was there not a notice on the box, or in it saying that you must preassemble and check clearances before balancing ? This is the reason they put that on the box.

Jan 18th, 07, 01:52 AM
Back again, my 496 pistons pin bosses need right at .100" in thickness to be strong enough to hold per ROSS.


Jan 18th, 07, 08:30 AM
Unfortunately I bought the crank as a no return since it was a second that had been ground .010 on the mains. I could not afford this crank any other way (paid $360). I guess that was a stupid mistake buying it. I couldn't find a cheaper forged crank for my 327 at the time it is way more expensive to build a 327 than a 350 due to crank availability.

I really don't have much option to change out parts either since everything has been messed with and I would lose out on a bunch of wasted parts. I prefer to keep the stock configuration of the 5.7" rods at this point. I do appreciate hearing the options though.

I would prefer just to have the weights ground down a bit if possible. Then I wouldn't have this problem in the future, however I may just go crate next time since this is becoming a pain and large expense. I am going to calculate just how much weight is actually going to have to come off to see how much of a balancing issue it will become.

I wanted to test fit the parts first but I have press fit pistons and the shop needed to balance before assembling the pistons and rods. I didn't like this but that was how it was done and I should have listened to my gut instinct.

Is the crank balanced on one axis only (around rotation) or for and aft as well?

Jan 18th, 07, 09:18 AM
I come up with worst case scenarios of 25.5 grams and 31.9 grams for the two weights.

Larger Dave
Jan 18th, 07, 02:15 PM
Or try and sell your good deal crank on e-bay as a fresh 10-10 regrind for 6.0" rods and apply whatever you get over your minimum bid (of what you have in it) towards another crank (either a first line scat or eagle or 5140 steel original crank for a stock 327 at std or 10-10). Your looking at two slugs of Mallory metal at $50 each plus a rebalance bill right now. So that amount plus your original "good deal" price should get you a new crank ready to run.

Larger Dave

Jan 19th, 07, 09:09 AM
I have looked around and it doesn't seem like there is much available for a 327 in new forged cranks. Eagle seems to be the only one I can find. If I get another Eagle who is to say it won't have the same problem?

Scat has no 3.25" stroke cranks on their site. Nobody seems to care about building 302's and 327's anymore.

My shop wants me to bring the mess in so they can tell me what to do before I wait two months. I will have to do it next week at the earliest since I am so busy with other things.

68Lemans blue
Jan 19th, 07, 09:42 AM
Good luck Bud ,I know your frustration,hang in there....have a beer for me too... :beers: Happy Motoring

Larger Dave
Jan 19th, 07, 02:52 PM
Neither Scat nor Eagle offer inexpensive forged cranks but all of their HD lightweight cranks can be had from 2.90" to 4.00" stroke (for a nominal fee of course).

There is an outfit in Utah or Missouri that I read about once that scraps cars for resale of the individual parts that might have a stock 327 steel crank in stock at a reasonable price. Apparently every car that is picked up as abandoned in the mid-west goes through these guys and they sort and check each part to see if they are rebuildable before offering for sale. I lost the URL but I'm sure they could be found with the right search parameters as they're not trying to hide.

Larger Dave

Jan 19th, 07, 05:12 PM
I'd see if a BIG Boneyard could scare one up using their WATTS line and cross country Boneyard Network.


Jan 19th, 07, 05:17 PM
Or, mark the spots on each side of each counterweight where the offending pistons hit and like you said, get a 9" angle grinder out and have at it!!

Try a crescent shaped metal removal first and then a flat if it's going to be short.

And I have seen cranks with short flats that locate RIGHT under each pin boss b/c of this!!

Then rebalance her and go!!

I say this b/c you are into this, this far SO you might as well finish her right..


Jan 19th, 07, 08:37 PM
While going thru all this, if you pistons have the pin locks groves and keepers, can you have those rods honed out to float the piston pin? This would ease some of your home assembly and give you a little extra free hp. If you do, be sure to drill and champher an oil hole in top of rod small end balancing pad. Once hole is drilled then have your shop hone this on a rod hone.

Jan 21st, 07, 11:45 AM
My pistons don't have locks. I wish they did now since I would have mocked the whole thing up before the balancing!

Right now I am looking at the cheapest being another Eagle crank at $509 plus new main bearings $50 and the cost of having the shop re-check clearances plus a rebalance.

If I can mange to keep the crank and hav some metal shaved off plus install two slugs if necessary and rebalance that will likely come in cheaper than the above.

At this point I won't know what the options are until I take it to the shop. Perhaps a used crank might be an option but I thought it would be safer and cheaper in the long run to get new originally.

I get you all updated once I get it to the shop. I do appreciate the suggestions. My first build is turning ou to be quite the learning experience.

Jul 2nd, 07, 05:34 PM
After grinding and rebalancing I have the motor nearly assembled. Hope to get it in on the 4th!

Jul 2nd, 07, 10:32 PM

I re-read my earlier post here and it looks like I forgot a few details. I will try to remember how it all went for me and my 383+cid Stroker motor clearance issues.
It’s been a couple of years and I have yet to fire it up.

My original order was:
Eagle lightweight 4340 48lb internal balanced crank, #(4350375057LA) ( A perfect grind as well), Wiseco ProTru #(PT025H4) 5.7 flat top 2 valve relief pistons, and Eagle 5.7" I-beam rods #(CRS5700B3D).

1st crank counter weights did not clear the piston bosses. Just like yours, hit the bottom of the pistons hard. 2nd crank with shaved counter weights did not clear much better either. Got a 3rd Crankshaft and we changed the pistons to SpeedPro # (138090) wrong pistons, then they shipped SpeedPro #(138095). Wrong again. Finally got SpeedPro Pistons # (138094) with 6” Eagle I-beam connecting rods # (CRS6000B3D). Finally all the clearance I could ask for.
I don’t know why the 5.7” configuration gave me so much trouble.

I was on the phone so many times with the folks at Eagle I was beginning to think that they thought I was incompetent and did not know what I was doing. The problem was definitely at their end. Quality control? Hmm!
I will say, they were patient, understanding and awesome to work with. Having a micrometer and measuring the parts helped big time. Thank goodness I was not in any hurry to build this motor.
They even absorbed all the shipping back and fort fees. That alone was a huge expense to them.
So even though all the aftermarket parts should have worked together, it became very clear to me that there are quality control, incompatibility, and or clearances issues between the various manufactures. So mock it all up and make sure it all clears and works before any machine work is to be performed.
Good luck!