Sizing connecting rod bushings
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  1. #1
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    Default Sizing connecting rod bushings

    I need to install some connecting rod (bronze)bushings and once installed they need to be sized to fit the piston pin. Using a Sunnen hone would be the normal (best) way to go, but I only have a few rods that need to be done and there isnít a Sunnen hone in the shop. Trying to avoid subletting things out if possible.

    Wondering about mounting the rod in the mill and using a barrel lap and Timesaver lapping compound. Obviously the proof is in the pudding, so I could try it and see how it goes. If done carefully I donít see any reason why it couldnít work.

    Anyone tried anything similar, if so what were the results?

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    Since you're in Canada, I won't recommend sending them to RBRE in PA. Otherwise I would.

    The problem you'll have lies in measuring the fit. It's such a small value. It'll almost have to be done by hand/feel.

    Personally I don't think lapping compound is part of any precision operation. I think you'd end up with a bunch of high and low and in between spots. Again, it's so small a tolerance that it might not matter. For a Briggs & Stratton, no problem. For a 9,000RPM 355" small block? Problem.

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    I did some for my tractor about 15 years ago. Pressed in the new bushings and bored them on the lathe. Quick, easy and no problems at all.
    Good luck, Mike

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    If these are typical automotive rods the pins will be between 7/8" and 1" in diameter. If that is the case they need to be straight and round to .0001" with .0003" - .0007" clearance. If you think you can hold those tolerances go for it. And be able to measure it. I almost forgot the big end and the small end bore have a center line that is parallel with each other.

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    Sunnen hone is not the last word when it comes to boring out the small or the big end of a rod . at work when it comes to installing bushings in none bushing rods or boring the small end on motors were the center to center is critical that's were the tobin arp rod boring machine comes in all the rods will be the same and depending on your skills you can get the job done on a lathe , mill or jig bore.

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    Quote Originally Posted by GregSY View Post
    Since you're in Canada, I won't recommend sending them to RBRE in PA. Otherwise I would.

    The problem you'll have lies in measuring the fit. It's such a small value. It'll almost have to be done by hand/feel.

    Personally I don't think lapping compound is part of any precision operation. I think you'd end up with a bunch of high and low and in between spots. Again, it's so small a tolerance that it might not matter. For a Briggs & Stratton, no problem. For a 9,000RPM 355" small block? Problem.
    They are for a 1000cc air cooled v twin that needs closer tolerance than the Briggs. Spins at maybe 5500. I’m definitely not suggesting that a barrel lap is the way to go, hence the original question. I think lapping has its place and you can achieve very high accuracy. Some folks use it for sizing the big end or the outer races of main bearings when using roller bearings.

    There is some info here. How To Page

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    Quote Originally Posted by mf205i View Post
    I did some for my tractor about 15 years ago. Pressed in the new bushings and bored them on the lathe. Quick, easy and no problems at all.
    Good luck, Mike
    In my situation, I don’t think I could achieve the desired finish and clearance without some luck, so would likely swallow my pride and take it to the guy with the Sunnen hone.

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    Quote Originally Posted by gappmast View Post
    If these are typical automotive rods the pins will be between 7/8" and 1" in diameter. If that is the case they need to be straight and round to .0001" with .0003" - .0007" clearance. If you think you can hold those tolerances go for it. And be able to measure it. I almost forgot the big end and the small end bore have a center line that is parallel with each other.
    I “think” it can be done. It’s a 7/8 pin and I’ll have to verify but they usually get a tiny bit more than .0007”. Maybe I’m in for a surprise, but keeping it round and straight shouldn’t be a problem. If installed correctly, I should have a relatively round and straight bore to start with and I won’t be removing much material. As for being able to measure it… good point. I have a few bore gauges, but nothing decent that will fit in a 7/8” hole, so guess I will spend some more money or find a shop that can be trusted.

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    Quote Originally Posted by 1yesca View Post
    Sunnen hone is not the last word when it comes to boring out the small or the big end of a rod . at work when it comes to installing bushings in none bushing rods or boring the small end on motors were the center to center is critical that's were the tobin arp rod boring machine comes in all the rods will be the same and depending on your skills you can get the job done on a lathe , mill or jig bore.
    Not sure there is one of those around these parts.

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    What do you have in the shop for equipment, and what size are you trying to achieve? If they were mine I'd prefer to do them myself, but I would ship them across the country before I'd try to lap bronze. I've seen to many prints with the note "no lapping allowed".

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    Did some tractor con rods for brother in law a few years ago. they came with recommendations to bore not hone for size. Something about better oil retention if I remember correctly. I would prefer not to use abrasives any way and risk getting grit embedded in the bronze.

    Dave

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    most rod bushing bore are smooth aka true but there are some that are not like the 390 ford the bore on them look like they were bored with a dull cutter and the idea there is after pressing in the solid bronze thin wall bushing there is a roller that pushes / locks the bushing in to the bore there are some that skip that steep and then size / hone or bore the bushing only to have a wrist pin knock after the bushing sets in the bore and then there's the ones were the top is narrower the the bottom there lots of fun to install and honing ya right with the bottom a 1-1/4" and the top a 1/2" wide good luck that's were boring over honing comes in

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    Wonder how much one can get away with here in this application.
    Bob

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    The tapered bushings can be honed but it takes a key way style mandrel

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    Quote Originally Posted by gbent View Post
    What do you have in the shop for equipment, and what size are you trying to achieve? If they were mine I'd prefer to do them myself, but I would ship them across the country before I'd try to lap bronze. I've seen to many prints with the note "no lapping allowed".
    The bike is British, early 50¬ís so clearances are slightly more than ¬ďnormal¬Ē. I still need to confirm the exact clearance required.

    2 lathes. Vertical mill, small horizontal mill MIG, TIG, arbor press, large hydraulic press, band saws etc.

    I’m using this stuff. Ok for bronze bushings.

    Timesaver Lapping Compound Yellow Label and Green Label Compounds, non imbedding lapping compound, manufactured by Micro Surface - Newman Tools

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    I just had some rod bushings done for a 1938 Pontiac. I pressed them in, but brought them to an engine building shop to do the Burnishing and honing to the specified 0.0003 ish clearance. My understanding is if you don't burnish them in place the can walk themselves either out into the piston - or in and block the oil hole

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    Quote Originally Posted by 1yesca View Post
    most rod bushing bore are smooth aka true but there are some that are not like the 390 ford the bore on them look like they were bored with a dull cutter and the idea there is after pressing in the solid bronze thin wall bushing there is a roller that pushes / locks the bushing in to the bore there are some that skip that steep and then size / hone or bore the bushing only to have a wrist pin knock after the bushing sets in the bore and then there's the ones were the top is narrower the the bottom there lots of fun to install and honing ya right with the bottom a 1-1/4" and the top a 1/2" wide good luck that's were boring over honing comes in
    These bushings are an interference fit in the rod. I haven’t measured the ID of the new bushing, but it is basically a slip fit over the pin. Obviously it decreases when the bushing is pressed in, but if pressed in correctly, it should be close to being round and true. Not removing much material. I would think, (but stand to be corrected) that using the mill for lapping would be a reasonably accurate way of doing it compared to the Sunnen. Seems to me that hand bombing the rod back and forth on the Sunnen would leave more room for error? But I’ve never used a Sunnen hone other that just the rigid portable ones.

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    Quote Originally Posted by gregoryd View Post
    I just had some rod bushings done for a 1938 Pontiac. I pressed them in, but brought them to an engine building shop to do the Burnishing and honing to the specified 0.0003 ish clearance. My understanding is if you don't burnish them in place the can walk themselves either out into the piston - or in and block the oil hole
    I believe it depends on the application.. at least it’s not something that is normally done with these rods and haven’t heard of it being done on other rods from British motorcycles.
    I recall reading something about a burnishing attachment for the Sunnen hone, but search everywhere and couldn’t find any info on it.

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    Quote Originally Posted by Cyborg View Post
    These bushings are an interference fit in the rod. I haven’t measured the ID of the new bushing, but it is basically a slip fit over the pin. Obviously it decreases when the bushing is pressed in, but if pressed in correctly, it should be close to being round and true. Not removing much material. I would think, (but stand to be corrected) that using the mill for lapping would be a reasonably accurate way of doing it compared to the Sunnen. Seems to me that hand bombing the rod back and forth on the Sunnen would leave more room for error? But I’ve never used a Sunnen hone other that just the rigid portable ones.
    there is a sunnen hone that has a jig that holds the rod and power strokes it but it looks like you have the tools to do the job just need some info to find a starting point

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    There is a fellow here in town that used to own a large machine shop. He has done quite a few of these particular rods so, although I was trying to avoid it, Iíll pay him a visit and see what he has to say about honing, burnishing, and lapping. Interesting enough, he has a Sunnen hone, but when doing the big end roller bearings, he uses a lap. Actually itís a modified Harley lap that they use for the same purpose. There is a distinct possibility that asking him about using a barrel lap will just get me a swift kick in the nuts.


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