I am building my new mini ram 383 with 6" rods when I was trying to degree the cam I rotated the motor and clunk one of the connecting rods hit one of the lobes on the cam has anybody had this problem? The machine shop that designed the motor, sold me the parts and did the machine work thinks it's a defective cam and they are checking on it. the rods are in correct but the one rod hits at the top of the boss on the large end of the connecting rod has anybody ever seen this?

 

On my 383 with 5.7 rods I had two that were hitting, I just ground off enough to get clearance and it's got over 1000 miles on it and going strong. You only need .30-.40 clearance so making that small adjustment will not affect balance to any real degree.

 

I DISAGREE!!!!!

After having put my faith in machine shop to help select parts for rotating group, paid good cash for a balancing job, and then grind some off!!! NOT IN THIS LIFETIME... Go back and tell them to clearance rods and do their job correct. And give you old balance sheet and new balance sheet. Your paying hard earned cash for a service, get it!!!
If the shop knew what they were doing or had did some investigating they wouldn't have this problem. Just my 2 cents.

 

Did the machine shop not have the cam when they did this work???

They will prob. suggest a small base circle cam, but that is an expensive fix. nothing wrong with the cam. Just have them finish their job.

 

genefree3 has a point.I had a similar problem with my 383. Two rod caps hit. I am doing all the work,to include parts selection, farming out machine work. Talked to the guy who did my machine work,his suggestion was to grind to get the required clearance then grind all rods the same. He said he could rebalance but it wasn't necessary.You grind off so little and the material removed, we're talking 1/10 gram here, is very close to the crank the rotating mass would never see any small difference. I guess if you were shooting for 10k on the rev meter it might but at sane levels it wouldn't matter. If I ever build another 383 I will spring for stroker rods and not be faced with this issue.

 

Is commonly know problem that certain rods will hit a std base circle cam in 383 engine.
Any competent shop should have been able to supply rods that clear or do machine work required to get clearance.

 

More than that if you remove 0.030 over a 0.5 X 0.5 in area thats about 1 gram. A 383 crank travels at approx 180 ft/sec @ 5500 RPM wich works out to about 0.39 lbs of force

now the question is how much imbalaced force can the bearings account for?

 

You should use a small base circle cam,the shop should of known that the price is the same .i would not grind on the connecting rods even a bit it will put the engine out of balance.just trade the cam for a small base circle cam and problem solved.I would not touch the rotating assembly if it has already been balanced it makes no sense to grind the rods for clearance even a small bit .

 

When building a motor you need to AlWAYS check clearances with a "mock-up" of the motor. In this mockup you need to have the cam degreed in to where you intend to run it. During this mockup this is where you check for clearances and do any "grinding" on the rods.....which is a pretty common occurance when building stroker motors. I had to clearance every one of my rods a little...using very good rods like Crower, oliver, and Lunati rods often helps reduce the amount that needs knocked off.

Once you complete the mockup then you take it all the to machine shop and they balance the assembly. You get it back and put it together with all rods etc in the SAME location and it should go together very smoothly.

This all take a great deal of time to get done right. But if you try to cut corners or assume it will all go together because someones did you will most certainly have an unpleasant surprise.

Don't cleanance then without a rebalance. Call the shop up and explain the problem (nicely as they will be the ones doing the balancing of the stuff and the last thing you need it to have them pizzed off at you....that seldomly get people very far, especially in this sport. )

A small base circle cam will also help, so let them check out the cam, and when it checks out which it will, then tell them that is the route you want to go. I had to go to a .880 base circle in mine to gain cleanance.....but you still may need to clearance the rods.

 

That isn't the problem. The machine shop made a mistake. The rod length isn't the problem. Neither is the 3.75" stroke. After all, Chevy make it work in the 400. The big end of the rod is wrong for that stroke. There should be no need for a small base circle cam in a 383. Have them order suitable rods for you.

RACE ON!!!

 

I should have made myself clearer, what I should have said was that I ground equal amounts off of every rod to keep it close to the same. My engine is not a race engine so I did not re-balance. A mistake? Maybe but I doubt it.

 

Ok I have my motor back they took the rod that was hitting out clearanced it then they removed all the rods and the crank and re-balanced everything they put it back together and called me at about 10:30 PM and told me my motor was ready they stayed late to get it done for me so I could get the rest put together this weekend now that's customer service by the way they took 1 gram off the rods they said that the tolerance for the balance is 1-3 grams for a 7,000 rpm motor but they rebalanced it anyway and got it between 0 and 1 gram. the rods are Scat I-beams and it is a large base circle cam

 

I can't say I really agree with their specs qnd tolerances, but I am glad they steped up to plate and corrected it for you. 0 to 1 gram is where I would expect them to be anyway.
Gene