Clearances on short block internals.

[matt texass]

This may be a dumb question but how do you change side clearance and crank thrust? Does it have something to do with the main bearings or rod bearings? In my mind I see the rods fitting on the crank and the crank fitting to the block one way without any kind of adjustment. I ask because I only understand enough to be dangerous to myself.



edit for thread title spelling (gig)

 

[Natural1]

Thrust is checked by placing a magnetic base w/ a dial indicator on the crank and zeroing it after the crank has been moved rearward to a stop. As I said, once the indicator is zeroed move the crank forward, read the dial and record your clearance.

You check your side clearance by measuring the rods and then subtracting the overall clearance at the rod journal. The most common practice is to use feeler gauges but when setting the clearance I don't like taking the rods off and on. I've seen people do that but it's easier to measure off the crank, subtract the rods combined width and machine to fit.

 

[matt texass]

How do you adjust it?

 

[US-1]

Side clearance is adjusted by milling small amounts off the sides of the rods. Thrust clearance is adjusted by sanding the thrust bearing (if too tight) or finding a thicker thrust bearing (if too loose).

 

[Natural1]

It depends on what clearance is required. I determine what to machine by checking the clearance at the rod journal, if the clearance is fine, then I determine by measurement, whether the rods have additional material on them. You have to do some quality control and check your parts. You don't want to machine your rods too much, if the crank is undersize in the rod area. I won't machine a crank to make up for rod clearance if the issue is an oversize rod. I fix the clearance issue, so that all the pieces last as long as possible. You machine the crank to fix a large thrust issue. If you don't have the required clearance the crank will have to be ground to allow. I have a fixture that I place my thrust bearings in if the clearance needed is small. I will bolt them up and take up to ~.0015" off of each side if needed. As the above stated, thicker thrusts to subtract clearance. This usually does the trick.

 

[matt texass]

This is why I love this forum. It amazes me that people "build" motors without have the slightest conception that concepts like this exist.

 

[Natural1]

As I'm sure SD can relate; when you play on a budget, you better know how to do your own work.

..or at least be able to check someone else's.

 

[matt texass]

So, it is commonly accepted that thrust clearance should be .008"-.012" and that rod clearance should be .006"-.018"?

I am also going to assume that you get lucky sometimes and that it just falls within these specs. Correct?

 

[matt texass]

As I'm sure SD can relate; when you play on a budget, you better know how to do your own work.

..or at least be able to check someone else's.

I try my hardest to adhere to this.

 

[Natural1]

I will let SD roll on with this one, as he is a resident engine builder but here is my take from Ron's build..

I still stand behind the belief that just because something is "within spec" does not mean that it should not be in a different area of the allowable tolerance.

 

[US-1]

So, it is commonly accepted that thrust clearance should be .008"-.012"

Yes

....and that rod clearance should be .006"-.018"?

No. Rod side clearance less than .012" is asking for real trouble. I typically run them out of the box because they usually fall between .012" and .014" (Manley h-beams). There are times when I will open that number up a bit based on the customer's intended usage. We have run rod side clearance as wide as .020".

A note on this: while doing Mike's engine (TexasBlownV6) I found the rod side clearance was .008" on his Manleys. This was with the 3.800" stroker crank from Kellogg. Obviously, that just wasn't enough. I then picked up another set of rods off the shelf and tried them. Again, .008". I called Kellogg and asked them about this dilemna. They stated that they have had reports of rod throws being a bit narrow on some of their 3.800 cranks. Mostly, the Saleen stuff that we had bought up. Apparently, this was why these cranks were on the shelf at Saleen. They didn't pass specs but had not been swapped out with Kellogg when the company went to shit. Not that there is anything seriously wrong with them but you need to check and adjust as necessary. I ended up side-clearancing Mike's rods to get a .015" gap and all went well after that. End thrust on the cranks have come up at .012-.014" so there's no problem with runout.

I am also going to assume that you get lucky sometimes and that it just falls within these specs. Correct?

There are times, yes.

 

[matt texass]

Thank you. ^^^

 

[EagleStroker]

There are times, yes.

And then there's the other 95 out of 100 builds.... It's fun matching parts and tolerances together.

 

[matt texass]

Onto ring gap. For a boosted application. Does top ring .022 to .024 and the 2nd ring .012 to .014 and the oil ring .035 to .080 sound correct? I would rather make sure than just taking the word of someone that someone told.

 

[US-1]

You don't gap the oil ring.

 

[matt texass]

Roger, thank you once again.

 

[Freaknazty]

Not something I would swear by nor is it the best way .............but it has a few pictures to give you a little idea on everything lol . http://www.svtperformance.com/forums/engine-tuning-214/461728-my-buildup-pics-description.html

 

[US-1]

Not something I would swear by nor is it the best way .............but it has a few pictures to give you a little idea on everything lol . http://www.svtperformance.com/forums/engine-tuning-214/461728-my-buildup-pics-description.html

You're kidding.....right?

I am not saying all are like this, but with mine, if you were looking with X-Ray vision through the block, all of my pistons came out with the writing on the rod facing the rear of the block, and all the little lock tabs in the rod caps for the rod bearings were on the left side...so the passenger side lock tabs were away from the center of the block (toward the passenger exhaust), and the driver side bearing lock tabs were toward the center of the block (toward the intake)...

Well let's not bother to look and see where the chamfer might happen to be.

Now the reason I said to use the old rod bolts for this is so you can get the caps broke back apart without having to have the special (expensive) rod/cap cracking tool...

just break the rod bolts loose, and screw them out a few threads....the put the socket on top of the bolt and tap it with a hammer...keep alternating between the 2 bolts with light to medium taps...2 or 3 and it will break loose

Yeah....let's bash the shit out of the rod threads instead of buying a $100 rod/cap separating tool. And if you're using the old bolts how the fuck do you get an accurate torque reading on the rod cap to determine bearing clearance? Once you change the bolts you have a different bolt stretch....thereby changing the torque spec for that rod and changing the bearing clearance.

 

[kyoshosp2]

Whattt SD u don't tap all your bolts with a hammer? I tap all mine with one lol. Some people ...

 

[EagleStroker]

And that is exhibit A why I don't work phones.