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Wrist Pin Clearance Question

whitebricks

whitebricks

New member
Joined
Jul 14, 2010
Location
charlotte, nc..../Boone
Have oversize Volvo pistons for my b230ft build.
23mm wrist pin size and new bushings installed in the rods.

Question.
The Green Volvo Manual i have, the dealer one, says they should be a slight thumb pressure to insert the wrist pin into the rod. Well mine go in great. but i think the machine shop might have opened up the new bushing a little to much. Also states that there should not be any noticeable play. i wouldn't say that mine is noticeable but with one person holding the piston down and one moving the rod around, we THINK we feel a slight movement, not sure. (and not the rod sliding on the pin towards the piston)

My measurements are as follows.
wrist pin=23mm
new re-sized wrist pin bushing in the rod=23.05mm (This is the biggest one)
Difference between Bushing and pin=0.05mm i didn't think this was bad?!

Machine shop says this difference is a general standard they use.:roll:

I trust the machine shop but want to also see what the turbo brick family has to say about this.:cool:

Thanks. Any positive input is gratefully appreciated. :)
 
the bushings are too large. Your MS did hone them out too far.

Your pistons/rods are full floaters. The wristpins 'float'. It is described as 'light thumb pressure' to push the pins through the piston itself, and through the bushing in the rod.

Your measurement of 0,05mm as being the radial clearance between the wristpin and the rod bushing is TOO excessive.

.....0,05mm is nearly 2 thou [0.002in]. THAT is more than 4 times too loose.

i.e., the radial clearance should be less than 'half a thou'....0.0005in.

Now, will that much clearance, and the resulting slop....wobble of the rod on the pin.....cause problems?

yes......sometime.

how soon? take a guess. Yours would be as good as anyone's.

I'd have the MS rebush and rehone the bushings to get the clearances where they should be.

good luck

TF
 
i ordered some new bushings this morning and then read your post, we felt the same way. thanks for the input, real helpful.
last build ran strong for awhile then ...knocked, sounded like a wrist pin? idk yet but just want to get this build right and not have any simple mistakes leading to ultimate failure. again:x:
 
whitebricks said:
i ordered some new bushings this morning and then read your post, we felt the same way. thanks for the input, real helpful.
last build ran strong for awhile then ...knocked, sounded like a wrist pin? idk yet but just want to get this build right and not have any simple mistakes leading to ultimate failure. again:x:
Click to expand...

I suggest you speak in "INCH" since the machine is doubtless a Tobin-Arp or Sunnen machine and is an INCH machine with set up jigs and dial indicators all in INCH.

Asking any automotive type to machine things to a metric dimension, especially one where the clearances are so small is asking for trouble.

And a minimum to set the clearance would be 0.013mm or 0.0006 or "six ten thousandths".
.0006 to .0008 is pretty much industry standard on floating pins---gotta have some place for the oil
 
I know for whiteblocks, there's is no real numerical clearance specified, the term used is "close-running fit". Basically, if two parts are size-for-size, they won't assemble by hand. A close running fit is just enough clearance that the parts assemble easily by hand without binding, but not loose. It's easier to have demonstated to you than describe with words though unfortunately. It's works out to basically, less than "1 thou", but more than "half a thou".

When you buy new mahles with pins, the pins will be the correct close-running-fit. You can use the amount of resistance of the pin in the piston to gauge how the fit on the rod needs to be. Has to be a new piston/pin of course though.
 
why did you have the rods "resized"? The machine shop can only make them looser than they were with thousands of miles on them.

go to the junk yard and buy 4 used rods and put them in the pin bushing will be tighter/better than what you got.
 
burstcurse said:
why did you have the rods "resized"? The machine shop can only make them looser than they were with thousands of miles on them.

go to the junk yard and buy 4 used rods and put them in the pin bushing will be tighter/better than what you got.
Click to expand...
Maybe you should go and watch the process---ya know? When they kiss off a little of the mating surface so the big end bore isn't round but more ()--smaller than the finished ID, then they hone it to size...


Or when you don't know something maybe ask things as questions and you won't write gems of wisdom like this you just did,:oops:
 
This looks like a good demonstration as to how rods are resized. Pressing in the new bushing to the small end is not shown, but instead described.

<iframe title="YouTube video player" class="youtube-player" type="text/html" width="640" height="390" src="http://www.youtube.com/embed/lzUa8kYLSRU" frameborder="0"></iframe>
 
burstcurse said:
why did you have the rods "resized"? The machine shop can only make them looser than they were with thousands of miles on them.

go to the junk yard and buy 4 used rods and put them in the pin bushing will be tighter/better than what you got.
Click to expand...

didnt have the rods resized.

instead i had new bushings pressed into the old rods
and the bushings have to be cut since the bushing will "shrink" when forced into a tight fit. so you have to cut or else the pin wont fit. at all

- now the pins are nice and snug. but still move like butter
 
John V said:
And a minimum to set the clearance would be 0.013mm or 0.0006 or "six ten thousandths".
.0006 to .0008 is pretty much industry standard on floating pins---gotta have some place for the oil
Click to expand...

funny. exactly what my machine guy said when i came back to him. no trouble. just told him we would like it a little tighter and they did just that and turns out that's the size they were honed to but however still felt a little to loose especially after last build ended in what sounds like a wrist pin knock? haven't cracked the old short block open yet don't really want to see anymore of the carnage.
 
whitebricks said:
funny. exactly what my machine guy said when i came back to him. no trouble. just told him we would like it a little tighter and they did just that and turns out that's the size they were honed to but however still felt a little to loose especially after last build ended in what sounds like a wrist pin knock? haven't cracked the old short block open yet don't really want to see anymore of the carnage.
Click to expand...

No problems. And no surprises either. Machine shop guy should know what is common knowledge---within the engine build trade.:roll::oops:
 
yeah yeah, but i like to look into things myself not just "take their word" on things, and the floating pin standard doesnt apply to EVERY floating pin assembly. most, but not all. not saying i didnt listen to what he had to say before i asked him to redo the bushings, im not going to believe everything people tell me. i like to get multiple inputs/opinions since things usually work smoother when you do that....
 
John V said:
I suggest you speak in "INCH" since the machine is doubtless a Tobin-Arp or Sunnen machine and is an INCH machine with set up jigs and dial indicators all in INCH.

Asking any automotive type to machine things to a metric dimension, especially one where the clearances are so small is asking for trouble.

And a minimum to set the clearance would be 0.013mm or 0.0006 or "six ten thousandths".
.0006 to .0008 is pretty much industry standard on floating pins---gotta have some place for the oil
Click to expand...

Are you set up to rebush rods?

Cost and turn-around time?
 
Can you buy the bushings from the dealer? Installing them is pretty easy, but honing is where the $$ is.
 
Dirty Rick said:
Not finding any bushings anywhere, except 2 weeks away from the mothership.

23mm pins not common to other motors.
Click to expand...

I couldn't find any as well. Looks like all the usual suppliers are out of stock.

If you need a set ASAP, I have a set of 100k mile 13mm rods sitting on the shelf. Or just go with the ebay rods, and know that they may need to be honed to fit the pins.

You could get a Sunnen rod hone for cheap btw: https://eugene.craigslist.org/tls/d/springfield-connecting-rod-resizer/6878942347.html
 
The problem with honing rods is the need to keep them square.
You need a fixture, not something you should do by hand. (at least not on my motor)

H beam rods 20#+ boost
 
Dirty Rick said:
The problem with honing rods is the need to keep them square.
You need a fixture, not something you should do by hand. (at least not on my motor)

H beam rods 20#+ boost
Click to expand...

It's usually done free hand-ish. There's a rod/dowel with a guide that you use.
You can also totally free hand it, I've done it on multiple rods.

https://youtu.be/5yqsEs8GG0Q?t=57

https://www.youtube.com/watch?v=SBIY-dtcbns

https://www.youtube.com/watch?v=e4h49GFKTEU

https://youtu.be/TX-eFEqAKaY?t=299
 
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