Quincy QR-25 Aftermarket Bushing Fitment Issue (Piston Pin/Connecting Rod Bushing)

I'm in the process of rebuilding my Quincy QR-25, model 340 (ROC 31) and as the title suggests, I'm having clearance problems with some aftermarket bushings for the connecting rod to piston pin. I can't even get the pins to fit into the bushings with them loose, and once they're pressed into the rods, the ID of the bushing will be even tighter.

I realize that digital calipers are not the best tool for this job, but they're all that's available. The ID's of the new bushings are 0.8730" and 0.8725". The OD of the piston pins is 0.8730" for the high pressure and the low pressure is 0.8735" at the end and 0.8730" in the center. So basically, the bushings are exactly the same size or slightly smaller than the pins. The assembly specs for this machine state the clearance to be .0004" to .0009".

The manufacturer of the aftermarket bushings says I'll need to install them in the rods, then have them honed to fit the pins. I had originally considered using a brake cylinder hone to accomplish this, but then realized that I can't even measure accurately enough to determine if I've got the proper clearance, so I'd likely have to hire this out to a machine shop. I'm wondering though, if I purchased genuine Quincy bushings, if this extra step would be necessary or if they'd be made so precisely that all I'd need to do is press them into the rods and the pins would just fit right (assuming my pins aren't worn).

I'd also like to get some feedback on the idea of reusing the old bushings, which I've "measured" to have 0.003" clearance over the pins. That's more than 3x the specification, so I'm guessing it would be a waste of time to re-install and just see how long they last, but I'd like to get the experts opinions on this.

As you mentioned, .003 is way too much clearance for a piston pin bushing. The absolute best way to do that job would be with a Sunnen Hone. The operator would need the pins, new bushings and the connecting rods. That way you can get a perfect fit that will be long lasting. I've tried fitting motorcycle small end bushings in the past with no satisfactory fit. After that, I always took them a machine shop with a Sunnen or similar honing machine with good results every time. Just my opinion.

Just to be contrary, jig grind the pins to size and position. On a more practical note, has the OP considered buying replacement rods? May be less expensive and easier.

I thought maybe the undersized bushings were intentional so that they could be honed to fit perfectly. There's a local machine shop called Quality Boring that does all sorts of small engines and outboard motors, I'm sure he's got a very nice honing setup and would be fully capable of honing the bushings.

As far as grinding the pins down, I'm not sure that would work because then the pins would be undersized in relation to the holes they go though in the pistons.

I'm really curious to hear about other people's experiences with installation of authentic Quincy bushings.

The price for complete aftermarket connecting rods with bushings & bearings is $460 for the pair. I've got $117 invested into the bushings and bearings, so even if I have to give the machinist $100 to make them fit, I'll be far ahead of the price for new rods.

standard procedure- install new pin bushing, expand/burnish id if called for and then hone to size or bore to size on a rod boring machine. Pin fitting is pretty much a standard operation for rebuilding an engine or compressor with full floating pins. It should not cost anywhere near $100 to have them fit at your local engine machine shop. A good shop will also check the rods for alignment when they fit the pins. The undersize bushing bore is absolutely intentional. OEM or aftermarket- it does not matter.

Thanks Dan, that's exactly the info I needed to know. I'll stick with my aftermarket bushings and move forward with getting them fitted. I'm new to the machining and engine building world, so I don't fully understand some of the things you mentioned...

Dan from Oakland said:

...expand/burnish id if called for...

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Is this a method of bulk material removal to get the ID close to spec, then the boring/honing operations would precisely dial it in to tolerance?

Dan from Oakland said:

A good shop will also check the rods for alignment when they fit the pins.

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Check the rods for alignment to what? The pin floats in the rod, then the rod is then fixed to the piston with a single screw.

ElginAgain said:

Thanks Dan, that's exactly the info I needed to know. I'll stick with my aftermarket bushings and move forward with getting them fitted. I'm new to the machining and engine building world, so I don't fully understand some of the things you mentioned...


Is this a method of bulk material removal to get the ID close to spec, then the boring/honing operations would precisely dial it in to tolerance?



Check the rods for alignment to what? The pin floats in the rod, then the rod is then fixed to the piston with a single screw.View attachment 268132View attachment 268133

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Even though you didn't thank me personally and profusely for my sage advice regarding having the bushings properly reamed and fitted, I'll still respond again. LOL.

Dan is referring to the possibility that the connecting rods could be bent. If one or both of them might be bent, your bushing job will turn out to be Ka Ka poo poo in short measure.

I'm just sayin'.

Check the rods for alignment to what?

The smart ass and correct answer is alignment with the crank. However it is a perpendicularity check with the pins. The inner bore of the new bushing may not be coaxial with the outside diameter. Then when installed, the pin clearance would vary from end to end interfering with proper lubrication and causing high pressure points on the pin causing premature wear.

This is why the idea of a brake hone is not a great idea.

Newman109 - Thank you for both your responses, you've been very helpful.

Bill - Excellent info as well, thank you.

Sounds like it's really a check of what both of you explained. By ensuring that the large and small bores are parallel it will prove the rod is not bent and that the new bushing will wear evenly.

This knowledge will be very useful, when I go to drop the parts off with the machinist, I can ask that he checks the "rod alignment" and I'll actually know what the hell I'm talking about.

It's funny when I watched the youtube videos on rebuilding Quincy compressors, there was only the briefest of mention that after pressing the bushings into the rods he would then "go get them fit." That snippet of information whizzed right past me until now. I thought the new bushings just got pressed in and bam the rods go back into service, good as new, but it's obvious to me now that there's a little more to it than that.

The deeper I get into this project the more I've come to learn that this is no simple task, several steps take the precision, knowledge and tools of a skilled machinist. I've been taking videos all through the process and a few photos which I plan to share in a thread documenting the rebuild. Hopefully it will be of some use to those in the future, who choose to undertake the rebuilding and restoration, of these finely crafted machines.

I rebuilt a 340 ROC102. After frustrating experience with aftermarket piston pins (were way too sloppy) I bought OEM. Perfect fit - strong thumb pressure to press them into the piston BTW, my rod has roller bearings, not bushings. Your ROC number is quite old.

You hardly need to be a skilled anything to use an adjustable reamer on a pin bushing........newbies do it every day rebuilding old motorbikes.

Lakeside53 - That's good to know, now I'm curious if the roller bearings could be retro fitted. It would probably require upgrading several parts to make it work though, IE. pins, rods, pistons. It sucks having such an old machine, apparently the piston pins for roc 31 are obsolete and can't be obtained from Quincy. I was trying to buy all OEM parts for my machine, but my local parts guy pissed me off. Seemed like he had no knowledge of these machines and every question I asked he had to email Quincy support to get the answer, taking days to respond every time. The final straw was when I asked what all came in the complete overhaul gasket kit, it took 15 days and lots of prodding till he finally came back and said it was just one gasket, which is obviously not true.

John.k - Do newbies obtain .0004 to .0009 tolenereces with those adjustable pin reamers? Now that you have given me the proper terminology for this I found a few youtube videos of people reaming connecting rods and it does look easy. Not sure how I'd check the rods for alignment or properly measure the bore with just a set of calipers, seems like I'd need more measuring tools for all that jazz.

Simple fact is your compressor does 900 or so rpm.,not the 10,000 that all the complex procedures mentioned so far are needed for.....As for fitting roller bearings,I have to assume the crank is one sided,and a complete needle assy can be fitted......you should note that rollers cant be run on a standard soft steel or nodular iron crank........anyway ,its all needless expense in a compressor.....My experience with compressors ,is that the plain shells used came from a car of the same era,and can be bought as car parts for a few bucks, not OEM compressor parts in a plain box ,marked up to hundreds.The rings are always standard too,and easily found cheap if you peruse your Perfect Circle and Federal Mogul catalogs.

OK,had a look at your pics.....car type rods,would bet what Im sitting on I could find car shells for the rods.......forget fitting rollers ,not possible with limited resources.....and as for silly tenths specs...its a compressor ,just a compressor....if the pin is fitted to a firm slip fit in the rod,its good for decades.Should be a thumb push in the piston,if piston is iron,...if ally ,then a hot water fit......Pistons do get hot in a compressor ,not as hot as an IC engine for sure,but hot enough to burn oil into carbon.

ElginAgain said:

Lakeside53 ..................................
John.k - Do newbies obtain .0004 to .0009 tolenereces with those adjustable pin reamers? Now that you have given me the proper terminology for this I found a few youtube videos of people reaming connecting rods and it does look easy. Not sure how I'd check the rods for alignment or properly measure the bore with just a set of calipers, seems like I'd need more measuring tools for all that jazz.

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While it's possible to use adjustable reamers for rough work, they do not leave a smooth surface. If you examine the cuts that they make under a magnifying glass, you will see highs and lows. The fits that they give are strictly from the high points and those are the first to wear down.

There are tool sets for Harleys that I've seen that have a fixture to hold the connecting rods tightly in the crankcase so that a reamer can be used. The reamers used in that setup are straight hand reamers, not the adjustable type.

.0004 to .0009 with an adjustable reamer? I sure doubt it.

You can not get .0004" to .0009" clearance with a reamer adjustable or not. Not to mention the surface finish will not be correct. Find an automotive machine shop in your area and have the hone the bushings.

I might try a reamer for a field "band-aid" fix, but I sure wouldn't do it if I could choose to have the fit honed. The burnish/swage just ensures that the bushing is firmly locked in place and as expanded as it's going to get so the fit doesn't loosen up as soon as the compressor starts running.

eKretz said:

I might try a reamer for a field "band-aid" fix, but I sure wouldn't do it if I could choose to have the fit honed. The burnish/swage just ensures that the bushing is firmly locked in place and as expanded as it's going to get so the fit doesn't loosen up as soon as the compressor starts running.

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There are no band-aids for machinery. As mentioned, those reamers are not the ticket for a lasting repair. Do yourself a favor and have the new bushings machine-honed. You will be glad you did.

Newman109 said:

There are no band-aids for machinery. As mentioned, those reamers are not the ticket for a lasting repair. Do yourself a favor and have the new bushings machine-honed. You will be glad you did.

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Sure there are, when you're working on a field equipment repair for a corporation that's losing hundreds of thousands of dollars for every hour that a machine is down. They don't care if it rattles itself to death and they have to buy a new one as long as it gets production going again long enough for the new one to arrive.

As I said, field band-aid yes. Otherwise no.