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Rod to cap matching
by
myvolkswagen
on 15 Mar, 2011 22:33
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Okay so I took my rods and caps to the machine shop to have them resized and arp pressed in. Problem being that my markings to match them are gone. I read that this may cause binding. However beings that they are resizing them does that mean I can match them as I please? I'm a nube so sorry if it's a dumb question. I don't know what to do if they were supposed to stay matched up
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#1
by
R.O.R-2.0
on 16 Mar, 2011 08:29
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you still have to have the cap matched to whatever rod it was machined on.. just because you got them sized, does not make them universal..
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#2
by
myvolkswagen
on 16 Mar, 2011 21:53
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They are separated so how would I match them up again? Not sure I understood what you said. I have too much money in this thing to screw it up with something that stupid
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#3
by
sdwarf36
on 17 Mar, 2011 03:21
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I have had to do it multiple times-its do-able. Like he said, look to line up the crosshatch. Also feel for any step at the parting line(where the cap+rod join)-and feel for the sides being aligned. After getting what you think you final answer is, torque them and 'fess up to the machine shop+ ask them to measure them for you,it becomes apparent very fast with a bore gauge.
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#4
by
myvolkswagen
on 17 Mar, 2011 09:24
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ill give it a try. thanks
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#5
by
RabbitJockey
on 17 Mar, 2011 14:09
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mine had the numbers cast in them i believe
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#6
by
myvolkswagen
on 17 Mar, 2011 15:25
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if they are put on will it be a very noticable binding? What about trial and error trying each cap with different rods until they fit? I dont know how well that would work. can the machine shop match them up by making measurements of some kind?
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#7
by
sdwarf36
on 17 Mar, 2011 20:20
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I have had to do it multiple times-its do-able.
Multiple times... and you're admitting it openly? 
Glad to hear its doable if I ever find myself in that predicament.
Yea-cuz I'm the guy at the machine shop that the people that mixed their rods up bring them to.
If you set you 4 caps + 4 rods near each other-play detective-look for coloring-stains-scratches that go from the rod to the cap-etc.Try putting the caps on the rods -you'll soon figure out the 1st--now your odds are better-keep swapping-when its right, there will be zero step from rod to cap. Tell you're machinist you think you got the right--but please check.
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#8
by
maxfax
on 17 Mar, 2011 21:21
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And, when you are sure they are properly matched up,
MARK THEM!
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#9
by
Mark(The Miser)UK
on 19 Mar, 2011 02:42
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Okay so I took my rods and caps to the machine shop to have them resized and arp pressed in. Problem being that my markings to match them are gone. I read that this may cause binding. However beings that they are resizing them does that mean I can match them as I please? I'm a nube so sorry if it's a dumb question. I don't know what to do if they were supposed to stay matched up
Don't listen to the wolves, once they have been machined, they are all machined to the same final size, unless you asked for3 thou off #1 and 7 thou off #4 
Thus they are all 'unmatched' to the engine.
Simply put two in, tighten lightly, then add one more at a time,rotating crank each time to check for binding.
With them all assembled, tighten further in stages, but not up to the final stretch with plenty of crank turning inbetween to check.
If you end up with one that binds, try one swap, if it follows the cap, it's the cap if it stays still it's the crank.
Either way wet and dry the final shell on the binding position under it's back...
This is how I'd approach the problem, as an Englishman and a gentleman 
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#10
by
maxfax
on 19 Mar, 2011 04:26
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Mark, I believe he has the caps mixed up among the rods.. At least that's what I'm assuming when he said this
What about trial and error trying each cap with different rods
The rods can indeed go in any ole hole (
) , but the caps and rods have to stay together...
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#11
by
sdwarf36
on 19 Mar, 2011 07:57
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Mark--you may be a gentleman-but your are giving out some pretty dangerous advice. Just because you may be able to turn over the crank does not mean it has proper clearance. Even plasticgauge can be deceiving in a case like this-your clearance may be fine up+down, it can be off on the sides. (note: the rod bore is usually .001 large at the parting line by design-usually built into the bearing.)
When the rods are made, the hole is small-and the thust faces (flat sides) are un-machined. The first step is grinding the sides-making sure they are parellel to each other-then the hole is honed out to the proper size-guiding off the sides to make sure they are at exactlly 90* to each other. You would think that the bore would be perfectly in the middle of the rod (if you stand up the cap + rod on their mating surface on a flat surface, the distance of the " 1/2 moon"from the flat to the high point of the rod + cap bore would be the same)-its rarely the case.
Example: rod A=1.001 cap A=.999--a nice even 2.000 hole
rod B=.999 cap B 1.001 -same even 2.000 hole
put cap B on rod A-your at 1.998-too tight
put cap A on rod B-you have 2.002--yes your crank will turn-but the hole is too large--and not round.
When you machine a rod, you start by grinding the cap(and depending on condition, the rod also)-its clamped in the cap grinder off the sides-then you grind away maybe .002 off it. Now when you bolt it together, the hole is oval- small up+ down. You now hone the hole back to being round-and to size.
If you have a decent machine shop, they will check the bores after putting the bolts in as a standard practice.
Here is a decent video of the process (I know-its a toyota-but everything is exactlly the same)
http://www.youtube.com/watch?v=lzUa8kYLSRU
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#12
by
Mark(The Miser)UK
on 19 Mar, 2011 10:54
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Sdwarf36
You are correct, We shall have to assume that they had the paired items, and machined them as a pair before throwing them into a 'lucky' bag, rather than standardising the whole batch.
Better to take some callipers and line them all up on a table, and check, either using a go/no-go basis, or make actual vernier measurements.
Checking an assembled joint in situ with a fingertip, can detect quite small slackness.
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#13
by
myvolkswagen
on 19 Mar, 2011 12:50
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I hope I can match them.
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#14
by
R.O.R-2.0
on 19 Mar, 2011 12:55
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you have a 25% chance of getting them right the first time..
i would feel at the parting line with my finger-nail.. and look for the machining marks, like was previously stated..