Hi guys,

I purchased an Eagle 499 stroker kit 4 years ago. I assembled the engine with a 400 block. The car was only used for street use.

I recently took the motor apart to repair a low oil idle pressure problem. The engine builder that assembled the block made a couple mistakes. He honed the cylinders to big. This is causing a lot of piston rock. The piston height is 1.120. Also the bearing clearances are incorrect.

I have a couple options to correct these issues.

1-Order custom pistons for my current 400 block and replace all the bearings.

2-Use another 400 block with the pistons I have but this block will need some work to clearance the crank to the block.

3-Order a new rotating assembly like a 451 or 471 which has a longer piston but I would need a custom piston or use a new 400 block.

Any recommendations on which rotating assemblies to purchase if I go this route.

Can I reuse my rods with the 451 or 471. They are 6.760

Look at the various kits and they'll tell you if you can reuse your rods BUT changing the pin height means you either a) change the rods or b) change the crank.

What about going the next size up with the pistons and bore and hone the block?

I could go with the customs piston but I will still have the short piston height.

Use your 400 block and 4.15 crank.

Have the crank stroked to 4.25 by offset grinding the journals to BB Chevy size, 2.20.

Buy .400 long BB Chevy rods (6.535) get them with BB Mopar width if you can.

Buy new 4.375 pistons with ~1.30 pin height, or 4.380 and hone to fit.

If you want a taller pin height, use a .250 long BBC rod (6.385) and a ~1.45 piston pin.

Did you actually measure the bore? It is quite common to rock the pistons at the tops on new engines when you push back and forth with your thumbs.

I will ask the engine builder tomorrow. The motor has 1500 miles on it. I was able to rock the pistons back and forth with my fingers. I think the builder said .003th piston to wall. I will double check.

Rocking pistons with a short skirt is a given.

as said the short piston will rock, & most forged pistons in that bore size will be a lot more than .003 piston skirt clearance, more like .005-.oo7

Can you expand on exactly was found. What are all of the clearances, bearings and pistons? What have you done to verify there are problems other than what the second guys tells you?

Most of the better piston company offer two different aluminum alloys on their forged pistons, one is a tight clearance, .0025 to .0045 and the other is much looser9.007+) for high RPM.
I prefer and use the tight alloy for my street motor builds
They still will move when pushed on the tops also

I don't like that short of a piston for a stroked bb mopar street motor.

I wouldn't mind it too much(although it wouldn't be my preference) in a bracket motor.

The problem with turning the crank to BBC pin size is the journals are probably mopar width now, so you can end up with a bunch of side clearance when you put a BBC width rod there.

Again, not really an issue in a bracket motor, but not what I'm looking for on a street motor.

I guess I'd wait to see exactly what all the clearances are before making a decision, but I'm kinda of the mindset to just put the rotating assy back in the block and sell it as a short block...... And start fresh.

I know there are other issues we've discussed on the phone about that motor(cr is higher than you want) that could require more $$$ being spent, and you still don't end up with what you really want, which may tip the scales if favor of starting over vs band-aiding what you have now.

How low is low oil pressure? How much piston to wall? How loose is the bearing clearance? Is there really any issue?
Doug

FWIW I run a similar setup. 400 block, 4.15 stroke and short piston. I have beat on it pretty well on the road course... repeated hot laps with plenty of WOT time on 1 short, 1 medium and 1 long straight. Also long street drives. It has taken it quite well. My main issue was a repop hemi pan. On the corners and heavy braking I had low oil pressure. Also hot oil running repeated laps with no cooler. I freshened it at 15k miles as a preventative measure. Bores, pistons and crank were fine. Bearings were getting to the point where they needed attention. FT cam also.

Anyhow, piston to bore clearance on the original build was dialed in to Ross recommendation for their high silicone low expansion forged alloy. Around 4 000's from memory. Bearings were something like .0023 on the mains and .0025 on the rods. OP is around 25 at hot idle and regulates to around 60-65 psi hot running. This with either 15W40 or 15W50 oil.

Based on my experience, the short piston B engine can work and live fine with clearances set close. In that respect, similar to the gen III hemi which is also a somewhat short piston engine.

FWIW, the freshen included some tuning. It is a fairly mild build yet makes 592 HP and 687 ft lb on the dyno... and has run on the track that way (and a bigger/better road race oil pan) and seems happy.

would some new bearings correct that issue just by changing them out? what OS pistons are those? depending on that ans could you hone for the next oversize or bore it out to that?. if they are the same weight or very close or can be trimmed a bit or the rod small end lightened a bit all to avoid rebalancing or a heavier pin to go the other way if needed.

I agree with everyone as it may not be as bad as you think. I run a piston to wall clearance of about .005 to .006. Mine called for that on a street/strip eng. And yes I could rock them a little and mine is an RB block. You may hear a little piston slap when its cold but that can happen when you run that clearance on some type pistons that run that clearance. Course depending on what you are after you may want to do what Fast68Plymouth suggested. Good luck what ever you decide , Ron

That's some good, real world experience type info there.

If the oil pressure doesn't go below about 15-20 lbs. I wouldn't worry about it. As long as it's right when running. Try a heavier weight oil? You can get pistons coated for extra clearance, say if the cyl. just needed a clean up hone.

One other thing you can do if your piston to wall clearance is really to much for the pistons used. They did it alot in the older days which is knurl the pistons. I did it on a 383 with stock pistons and worn cylinders. Knurling raises the surface on the skirts and then I file fit them to the spec I wanted. The knurls also hold oil which helps keep oil on the piston skirts. I put many miles on that 383 and I used over size rings I file fit. Never used any oil and ran good. Ron

Guys it is probably best if I start from the beginning so everyone is on the same page. This is used only as a street motor.

I used a brand new 499 rotating assembly from Eagle with a standard bore 400 block. The block was honed to fit the pistons and line honed. Not sure exactly what is was bored to. Engine was assembled and the motor worked great. It had 25-30 oil psi at idle. At 6000 rpm it had 75 psi with a standard volume high psi pump and 15w50. According to the engine builder the mains were at 3.1 - 3.5 th and the rods were at 2.2-2.4 th. The motor made 500 hp and 550 tq. with a solid roller and dual plane intake with manifolds. Motor had roughly 1500 miles on it. I had to run 93 octane in order to not have any detonation. Any lower octane would cause the motor to detonate. I added headers and the motor made no difference in power. Compression 10.8:1. Piston is .015th in the hole. (aluminum heads)

I decided to contact Dwayne and change my combo. Dwayne designed a cam. I went with a solid FT. I had another engine builder take the motor apart and check all the bearings clearances. He rubbed the cylinders and line honed the block again. He said he set the mains to 3-3.5 and the rods to 2.5 - 2.8th with new bearings. (He was full of BS.)
Reassembled the motor and the motor had around 12-15 psi hot at idle and 52 psi hot at 6000 rpm with 15w50. I really did not like the oil pressure. This combo has 500 miles on it.

Thanks to Dwayne the motor made 590 hp and 640tq with a cam change, single plane intake and tti headers. The motor still needed 93 octane but I never heard any detonation.
Compression 10.9:1 Piston .015 th in the hole.

I figured before I damage it let me take it apart and check the clearances.

I am on my third engine builder. Hopefully I have better luck this time. According to the new engine builder the piston to wall on the skirts was 3.5 th. Mahle states that if the block is bored to 4.375 the piston from Mahle has 4 th built in. I cannot understand how this is possible. Unless the block was honed lower then 4.375 originally.

He mentioned the very top of the pistons had 30th piston to wall. I guess this is the piston design because there is no scuffing in that area.

He found the mains at 4.5 th and the rods are at 3.2 th. The second engine builder used a Clevite X bearing on the rods. If I used the rod bearings that came with the kit that should tighten the rod by 1 th.
He wants to line hone the block, cut the caps and rub the cylinder walls. We even discussed tightening the bores to 2.5th. Maybe using new pistons or 2line2 coatings on my original pistons. Side rod clearance was .030th.


I might fix the oil problem and sell the short. Start fresh with a different cube. I am really getting tired of pulling this motor. I am getting good at it.

Its to bad you can't find and keep a good engine assembler
As far as the tops of the piston being smaller in diameter than the skirts , they need to be that way due to the amount of combustion chamber temps held above the rings, the tops will and do expand a bunch more than the skirts do
I like all my Hi Po engine clearance, street or race, tolerances looser than tighter, these are toys, not long distance cross country econ cruisers Tight will stick, loose will not
Good luck on finding a solution to happyness

Main clearance is pretty high at .0045". Probably why OP is low. Rod clearance is kinda high also. Still, at 15psi idle/50 psi running oil pressure is not dangerous low. I might be tempted to run it and enjoy it while you plan and collect parts for your next build or re-build. A high volume oil pump (I think you have standard volume?) would help the oil pressure situation somewhat.

Piston to wall clearance should be set based on piston manufacturers recommendations + engine builder experience for piston and alloy type and application. This will not affect oil pressure to any meaningful degree.

Also, FWIW, 4.375" is an over bore for a 400 block. .035" from memory.

Why did you have this done?

Why not back to the original builder?

Who did the first dyno run?

Who did the second dyno run?

Once the oil pressure is fixed, what is wrong with this motor? And exactly what problem are you solving by selling this motor and starting over? A perceived piston rock problem? If you do another motor, will you use the 3rd builder that tells you have 30th piston to wall, or will you get a 4th engine builder?

BSB67, I had it done because I wanted to double check the bearing condition because the solid roller cam was not installed properly and it kept eating the distributor gears. We found the end play 1/16th. I figured lets double check everything since we have it apart. That is exactly were the problem started. I should have left it as is.

I am not having any luck with engine builders. The first builder is out of business.

The second one dynoed the motor the first time and the second time. Great guy but I don't trust him. He built another big block chevy motor for a friend and the clearances are also all wrong. The guy builds full out race motors but I really think he isn't the best at street motors.

I was only thinking of building something new to fix the short piston, and lowering the compression.

I could fix what I have, but I might have to get custom pistons to lower the compression.

It really sucks paying people over and over but I can't find a good engine builder. The third engine builder has been around for years building street motors. He has done a lot of Chevy motors but I don't think he does a lot of Mopar builds.