My 383 short block is coming together. I got 010 block bored with KB hyp pistons and .0025 clearance. Cam bearings are in. Now the crank and rods. For the rods is there a big difference between the two types (bushed/pressed) and can someone explain the pros and cons for me. THX

 

The bushed rods take a floating pin. Somehow that is supposed to be worth a horsepower or two. The biggest thing *I* prefer is that you can assemble the rods to the pistons, at home. You don't even have to install the pain in the azz locks for trial assemblies. Unless you have a pretty well equipped shop, you'll have to have the machine shop install the pistons on the rods. If you had such a shop, you wouldn't have asked the question. Almost all factory set up use the pressed pins. They're fine for an engine that won't be apart and reassembled many times or often. Some have had the locks fail with disasterous results.

RACE ON!!!

 

I would not use full floating. I had full floating on my speed-o-motive 383 kit & 2 of the rods were sliding fore & aft on the pins :eek:
Pressed pins - way more reliable IMO

 

Dude, your clearances were bad/excessive.

The floating pins came in the factory engines designed for relatively high RPM's (and remember those guys/engineers were pretty bright). And if you take your engine down for inspection/maintenance periodically, the floating pins are preferred for obvious reasons. The lock rings can be a pain to remove if you're not accustom to doing it however. I've always used the floating pins in high performance engines.

 

I am not arguing with someone who prefers the method other than my preferred method, but ???

With floating pins, the pin is not free to move in the piston. The pin is just long enough to allow the installation of the locks. The rod can move on the pin within the confines of the pin bosses of the piston.

On pressed pins, the rod doesn't move on the pin, but the rod and pin, pressed together have the same range of movement. The piston has no locks to limit the pin movement in the piston.

The piston pin bosses are the travel limiter. The difference is that on a pressed pin set up, the rod and pin move as a unit. The relative movement is between the pin and the piston. On a floater, the pin doesn't move. The relative movement is between the rod and the pin.

The amount of, "sliding fore & aft" is no different between the two methods of pin retention.

RACE ON!!!

 

Bushed is bested it gives freedom of movement. The locks can be a pain, but not to bad once your have done a few.

 

It seems like just the fact you could put assy together yourself with bushed is a great reason for bushed. You never know when eninge might come back out. I was thinking the extra flex of bushed cant be bad either. I have spiral locks which come with KB pistons so I'm stuck with those unless I can change to "c" kind.

Is added clearance for bushed an "extra" slop that should cause concern?


[Modified by Surfer69, 1:34 PM 5/12/2004]

 

nope. you fit with ~ .0005" pin-to-rod, and the same pin-to-piston

PS: stick with the spiral locks, much better than the "c" type.


[Modified by 66427-450, 2:50 PM 5/12/2004]

 

I knew I was gonna stir the poopie on this one. I know that all the racers use full floating for whatever the obvious reasons are - mainly for ease of removal/installation. The big ticket teams change these items regularly so they never become an issue.

I'm just stating that I had problems with them which caused 2 rod bearings to fail. It could have been speed-o-motives kit or their poor assembly chks.
In any case, I've never had a problem with wrist pins or rod brg failure until I stepped up to bushed rods.
I'm not the only one that feels this way - some top engine builders stay away from them too.

 

How does the bushed pin cause rod bearing to fail?

 

I wasn't arguing or trying to convince anyone that one method was better than another. I was merely pointing out the differences and that the movement, relative, to the rod and piston, was the same.

If you haven't seen any of the posts, do a search concerning forum members satisfaction with Speedomotive. The question has come up on quite a few occassions.

RACE ON!!!

 

A few years ago, my fairly new speed-o-motive 383 with about 7,000 miles started making noise on acceleration under a load. I searched forever to find that noise, but it was hard to duplicate in the driveway.
I changed all the lifters, cam, chain, fuel pump, ballancer, etc..I could not find any visible problems, either.

I was ready to pull the motor & tear it down when I decided to pull the pan again I look one last time. As I was lying on my back looking at the bottom of the motor, I decided to put a wrench on the harmonic balancer & turn the engine to watch everything moving.
That's when I found it: The # 1 rod would slide (on the pin) toward the front of the motor as the piston went up, & aft as the piston came down. It would slide almost the entire length of the pin. The bottom of the rod would just pivot, but seemed to be secure.
I pulled the rod cap off and the bearing was destroyed and it chewed up the crank too. I found a similar condition on the # 6 cyl, but not as severe.

Long story short, Speed-O-Motive would not even give me the time of day on this and they were rude. The said I was spraying Nitrous & would not help me. I told them that I never used Nitrous (this kit was supposed to be ok with Nitrous anyway) That was it.

My guess is the holes in the rods were not straight (Eagle 6" H beams) or the crank throw was off slightly. The fact that the pins were floating made matters worse by the fore & aft movement at speed.

Since then I have done a lot of research on the differences between press fit & full floating. Pressed pins do have an increased friction factor at high speeds, but they also have a solid "T" with the rod & pin which increases strength, which full floating doesn't. If my rods had presses pin it probably would have been ok.. :(

I feel that that full floating pins needs to have everything aligned perfectly to avoid problems - Not a problem right after a rebuild, but it may be different after 25k miles stop and go traffic on the 405.

:cheers:

 

well, it sounds like there was some significant problem, that's for sure..... but surely don't think it could be the result of a properly fit floating wrist pin.

 

How do you know about the 405, your from Conneticut? :lol:

That's interesting about the sliding but had it been pressed with those preloads caused by the crank and rod, it seems like you would have failed earlier not later.

 

Quote:
well, it sounds like there was some significant problem, that's for sure..... but surely don't think it could be the result of a properly fit floating wrist pin.

You might me right. I think the full floaters made the problem bigger tho.

Surfer69 - I lived in your area a few years ago (Hermosa). I drove the 405 daily.
Is Polly's still open at Redondo Pier?

 

that is caused by rods that the big end and the pin end are not parallel and square to each other. any good shop should have a fixture to check this alignment. :chevy