Replacement of Connecting Rod Bearing

[vesnyder]

Is it essential to replace the bushing/bearing on the connecting rod on the small end (piston end)? Seems like I've seen plenty of crank bushings for sale but have not seen many piston end connecting rod bushings?

I am a rebuilding my first engine and should have plenty of newbie/basic questions over the next several months?

[Ken911]

when you get the rods out send them out and have them rebalanced and rebushed, make sure you send the new rod bolts along so everything will be balanced correctly. there are several people here on this board that shops that do this

[afterburn 549]

One side pt. genuine P. bolts are one time use only......so make sure they do not use them for anything else then balance or go bling for ARP bolts

[dion914-6]

Hey Vance, what ya building? I agree with Ken911, just send them out. It's cheaper to have them done right by someone who knows what they are doing.

I'm still S L O W L Y building the RS engine for the 914, and this is one of the next operations for me too.

Who does the list recommend to have these done at a reasonable cost/time?

Dion

[davidppp]

Hello there.

Not essential provided all is in spec.

The main thing to check is the cap end for roundness: the small end is often just fine..

Kind regards
david

[engguy]

I have spent many years doing overhauls on all kinds of engines, and yes as a job in a dealer ship as well. Large expensive stuff, industrial diesels etc. The manufacture had what is called reusability guidelines.
Certain parts are always replaced, such as bearings etc. As far as a diy deal. It depends on the condition of those bushings, and how they check dimensionaly. The big problem is, you can spend the $ for perfection in the parts for the build. But there are a couple of variables that could always crop up and bite you. No part is perfect, you can have a brand new part that has imperfections with in the materials and could break. Old used parts can be close to their fatique limits, and fail. And the most important element is who is doing the build? And how picky and knowledgable is the person, and how skilled at spotting a problem, and dealing with it? Lots and lots of amatures have acted as engine builders, and lots and lots of them will sometimes run and run okay. But that doesn't mean the job was done correctly. And then there are the ones that end up advertized forsale, saying "Its apart for inspection, I just don't have the time to put it together" meaning maybe theyer not sure how to do it? Then there are the ones that blow up on start up, or 100 miles down the road, or after a week it dumps all the oil.
Personally I wouldn't say a Porsche engine is for someone that doesn't know mechanics or machinist type work. It maybe less expensive in the long run to have someone that knows these things do the assembly.
I know I would not want to spend the dollars to purchase a car that had a learner and trainee in mechanics, do the so called engine rebuild.

[davidppp]

Hello, engguy.

Have you done many 911 motors?

Kind regards
David

[dion914-6]

Mr. Engguy, I would encourage you to spend more time reading posts on this site. You have probably unintentionally told 90% of the people who frequent this board that they have no idea what they are doing and have no business building engines as amateurs. One of them is me, but I won't take offense because sometimes I ask myself the same question! However, after successfully building Type4's, Formula Vee engines and now flat 6's, I consider myself a fairly good wrench. Look around, you will be surprised by the number of backyard mechanics on this site that I would trust my engine with over a dealer any day.

Back to the subject at hand - Vance, I have also gone both ways on this subject. Most of the 4's I built were by re-using the rods after checking them for spec. However, with the amount of money going into the 6 rebuilds, I practice a better safe than sorry approach.

Good luck with your build and let me know if you need a hand with anything.

Dion

[afterburn 549]

There is no mystery if you have a map and advise. The P. eng. is a little different then Most recipes...but not beyond what a determined person is able to do.
I am living proof.

[engguy]

7, and many of other brands as well. Also many powershift and automatic transmissions, even some aircraft engines in the past.

I'm the last guy to say trust it to a dealer. Don't take nothing to an outfit that pays the guy doing the work by flat rate. He/she is gona do the fastest crap job they can, that is how they make money.
My brother told me about one of his cars years ago, he just did all the front end work, replaced everything, and left the bolts somewhat loose, and took it to an outfit to have an alinement,
he see's the guy with an airhammer and chisle trying to loosen something and slipped off and gouged"cut" into the unitbody, all the parts were painted pretty, etc. that is what happens to your stuff when you take it to a goof ball outfit and let the average disrespectful idiot mechanic work on it. You can always spot them by the big talk they talk.

[davidppp]

Very good.

So, what advice can you give about the small end bushes please?

Have you seen problems with reuse if in spec?

Kind regards
David

[engguy]

I agree with what you said in your post above. I have done many with out changing them.
There are alot of cases where a person can cut corners especially on his own vehicle, to keep costs down. If you were doing it for someone else you would want to cover your rear and do it all very correct. Or talk it over with them if they want to save $ on the overhaul.

[Henry Schmidt]

It is my experience that, after running an engine, if you separate the rod cap from the rod, the big end should always be rebuilt. Rebuilding the big end is something that should be left to an expert. There are many, just make certain they have the correct specs. It is preferable to pick a company that can size to length not just diameters..
As for the small end bushing, this is one of those "it's so cheap why not replace it with a new bushing?"
$8000 overhaul and you (editorial you)want to save $60 on bushings?
Rebuild the rods, both ends and don't forget to replace the bolts.

[engguy]

"If you separtate the cap from the rod" ???? Yes you replace the big end rod bearings. What do you mean by rebuilt? If it is not damaged there is no reason to have to remachine it. And yes its a good idea to replace bolts. I have never had to do that on american auto engine overhauls ie the budget ones that is. And never had a failure from it.
Same goes for many large industrial engines and that is at the dealer.

[davidppp]

Hello, engguy.


I'd listen very carefully to Henry..
In my tiny experience, it is a matter of revs.

Most Every race engine I have done had big ends out of round.

I don't care whose rods..cosworth, etc etc all go out of round..

Kind regards
David

[Henry Schmidt]

Hi engguy, new to the board and already you're the expert.

I see you have built 7 Porsche engines. Good for you.
I will admit that I don't build American V8s, big diesels or aircraft engines but I have some experience with the flat six Porsche.

When you spin a reciprocating engine the big end journal changes shape, much like an egg. The higher the RPM the more the distortion. Porsche engines run at RPMs quite often well over 5000 and this constant distortion causes the rod to take a set. What I mean by that is the big end becomes out of round. Heat cycles and rod bolt stretch add to the phenomenon. When you separate the rod it never goes back to the exact same position. Depending on the piston load this generally happens slowly. The rod bearing has a chance to adjust to these gradual changes. If they happen quickly to bearing is toast.
Rods like Carrillos, Pauter and Pankle rods resist this distortion better but they all do it.
Now if the rod is no longer round (and at least 25% aren't round) then when you install a new bearing in a oval hole the life expectancy of the bearing is greatly reduced.

In conclusion, low RPM engines( diesels, big American V8 and even 2400 RPM aircraft engine) may survive with minimal resizing but high RPM engines require special attention.

[efhughes3]

Originally posted by engguy
idiot mechanic : You can always spot them by the big talk they talk.

Hmmmmmmmmmm