As long as these pistons have the valve relief up; the chamfer of the rod should always be on the piston's left whether it's installed in the left side, or the right side.

 

Assuming all rods were pressed onto the pistons with the chamfer correctly oriented to the left and the piston/rods are all zero balanced, what are the negative effects of continuing to run the engines as is?

 

Do Small Blocks have offset wristpins in the pistons? I thought some V8 Chevy's had this to control thrust wear. If so, wouldn't mounting the pistons wrong, switched, upside down caus block wear issues?

Knew a guy that raced circletrack bomber stuff. He'd frag a piston, over-bore only that cylinder and put it back together with the correct oversize piston. By years end he'd have all sorts of pistons in the motor, sometimes flat-tops next to domes next to low compression recessed tops. Idled really poorly but revved like stink. A little lower on power I would imagine but cheap...

Tom

 

Budget is important, but my main concern is longevity.

 

What would make you think that shop that couldn't even put the pistons in the right holes would have balanced the motor correctly?

You could pull the pan and see if the bottom of the rods are stamped with a number and possibly a stamp on the piston near the pin bosses.

There is two schools of thought about balancing. old school take the heaviest rod and lightest piston and on down the line and make each of the "SETS" weigh all the same. Then they have to stay as a matched set. Or the best. Make all rods weigh the same as the lightest one and the same with the pistons. Then any part can go in any hole.. So when you burn a piston. You can go to your notes on the motor and make a piston to match the set

 

I heard the shop is under new ownership.

I am going to get the the motor ready to come out. Stay tuned..

 

At this point I would be mostly worried about the rods being in correctly. The tabs of the cap or side where the bearing locks go to the water jacket or outer side of the block. The balance of the motor may be an issue, but it might be alright if it truly ran vibration free before. If the rods and pistons are swapped around and they still dont match up then You will have to recheck piston to valve clerance. Also if pistons are swapped around it would be a good idea to have the piston to bore checked, to be sure its not out of spec. You also have to watch for rod journals that may have been ground smaller than others. In .01 / .02 / .03 increments. Better to be safe than sorry.

 

I definitely want to error on the side of safety. If I decide to pull the bottom end back apart, everything will be checked.

Yes, there were no vibration issues. The motor ran smooth up to 6500 rpm.

I am doubtful of any under sized journals or chamfer issues, as the motor ran for several thousand miles without knocking or producing metal in the oil. Then again, you never know until you tear it down.

 

From my personal experience......
Dont take it back to the same shop that make this rookie mistake.

It happened twice to me and both times, I took it back.
Sure, they fixed it for free........but the same guy worked on it. Made me nervous.

Now, when some shop shows rookie mistakes......I am willing to pay again and take it to another shop. I have finally found one I like in Dallas, TX.

 

If the pistons are clearing the valves it won't hurt anything. I would expect that rods in wrong would have showed up by now with metal stuff showing up in oil and everywhere. The pistons themselves don't know what hole they are in as long as they don't smack anything.

JIM

 

Jim,

Other than valve clearance is there any induction issue or loss in efficiency from having the smaller relief on the intake side? I know that is a bit of a loaded question, but what the heck.

The motor may receive a cam swap in the very near future. Although I currently have clearance, I want to be prepared. This is a budget build and I am trying to work with the parts I already have on the shelf.

Valve clearance numbers:
Pistons in the wrong hole - *aprox 1/4 or .250
Pistons in the proper hole - *aprox 9/32 or .28125

*clay deflected so it was difficult to get an accurate measurement

Current Cam:
Comp XE284H
Hydraulic flat tappet
Dur @ .05 - 240/246
Lift .507 .510
LCA 110

Possible Cam (VERY open to suggestions, I know very little about picking retro fit roller cams):
Comp Magnum 304HR
Hyro Roller
Dur @ .05 - 244/244
Lift .600 .600 - leaving about .157 of clearance
LCA 110

Motor:

• 357ci - 10.1:1
• KB 7cc relief pistons
• Zero deck
• Dart Pro 1 215cc (the older version) - I know these might be a little too much for the small displacement, but it is what I have on the shelf. I got them at a discount for $600 and couldn't say no.
• 1.52 Comp Pro Mag roller rockers
• 1 7/8 Hooker side pipes
• Air Gap RPM - port matched and cleaned up
• 650 Barry Grant Speed Demon - Again, this is what I have on the shelf and a new carb is not in the budget. I recently spoke to a tech at Dart who said, "the 650 BG would flow enough air and help compensate for the over sized heads by keeping air speed high." Not sure if this is true, but is sounds good?

This is not a daily driver, so I am ok with a very choppy idle. I also enjoy winding it out frequently.

Any suggestions on roller cams and thoughts on clearance issues?

 

Apparently they haven't been hitting the valves, but the radial clearance is, of course, marginal with the intake valve going into the exhaust valve relief. Many pistons have symmetric valve reliefs, but those that have asymmetric reliefs are specific to the cylinders - the larger intake valve gets a larger relief than the exhaust valve.

If you switch cams, using a larger intake duration which opens the intake valve sooner, or if using a tighter lobe separation angle, or if advancing the cam, or if using a higher ratio rocker arm, all of these open the intake valve sooner and farther, and will decrease valve to piston clearance of the intake valve.

 

I would just run it as is and not worry about it. I'm not saying that's the smart thing to do, just what I would do......


Scott

 

If the current cam stays in the motor, I may leave it as is. If I change cams, that is a different story.

Could you chime in with your cam knowledge? Is it worth it to swap? Do I really have much to gain by going to a roller with my hodge podge motor combo?

Larry, you hit the nail on the head. The radial clearance is very marginal. The clearance numbers I posted above were the depth parallel to the valve travel. The clearance at a 45 degree angle to the piston from the intake valve top edge was much less. If there is radial movement, they may hit.

This begs the question, what is the chance of radial movement with new guides? Are there other factors that contribute?

 

Id be very leary about puting the roller cam in without sorting out the pistons first. I would leave everything as is unless You are looking to gain .1's secs in quarter mile times. What I meant in My earlier post was that if a crank has wear or damage on it even from the factory. It is comon for them to grind just one rod journal rather than grind them all to the same size. Then the rod bearing becomes specific to that journal.Just My 2 cents.

 

Still got the goat ?

 

New guides will help remove radial slop, but, I'd like to see at least .030" clearance radially. Further, if the fly cuts in the pistons are radiused at the bottom of the cut, as vertical valve-to-piston clearance is decreased, the valve edge gets still closer to the radius wall. On the other hand, if the bottom of the flycut is a sharp 90 degree angle, any decreased vertical clearance won't affect the radial clearance.

 

Yeah no one has come to claim their prize

 

You make a very good point about the fly cuts. If I plan to convert to a roller cam, this piston issue must be addressed.

So I guess I need to decided how much of a benefit, if any, a new roller cam will bring. Then decide if that benefit is worth the cost of rebuilding the bottom end...

 

You're getting excellent dead on the money advice from Larrywalk.
Theoretically the reduced clearance around the valve at overlap *could* affect the flow..but I doubt you'd ever measure it in real life. So if you want to leave it as is...it will run that way forever.

If you already have the motor out it makes sense to do some piston swapping. If going through all of that piston pressing on/off I'd surely change rings while I was at it and give it at least a quick brush hone for a motor like this.

On to your combo...if you're going to swap cams, definitely get pistons straightened out now.

You've got a pretty mismatched combo overall. Not that it won't run well..but we have relatively small cubes, big heads, too big of headers, a dual plane intake and a small carb. Whew! We're all over the place....but it can all sorta compliment each other.

The heads and headers are all ready for 7500 rpm shift points....the dual plane will die out in the 6500-6800 rpm range...the small carb would do better on a single plane than a dual plane, the RPM range we're talking about isn't really conducive to long life with hypereutectic pistons...and it would really be better with a solid roller to spin that RPM easily. Small blocks with HR cams "can" rev to the 7000 RPM range with decent parts...but it takes a real nice combo.

What is the trans and rear gears? We can try to spec a cam that will help bring all of this combo closer together.

Can you trade your shortblock for a 400" one and put your heads on it??

JIM