Redneck wrist pin bush honing...

[mungus]

Have finally got around to prepping my spare 390GT motor parts, into a complete kit, ready to be built into a 68' OEM spec Mustang GT engine (spare for my car, which has a warmer one fitted).

While cleaning and inspecting the rods (matched set of C7AE-B's) I found one with a damaged wrist pin bush (one end had a wee bit broken out). The rest are great; look nice, no marks, pins run butter smooth and within spec. So no problem, sourced one new Clevite bush and am now ready to fit it.

However I live in the country and don't really want to wait months in line for my trusted machinist in the city to get around to honing this one bush (if required). With COVID it seems every man and his dog has got around to their projects and he's swamped. So as I'm a careful general engineer and trust myself not to be stupid, so I'm thinking I'll do this small job myself.

So my question is this. Has anyone used a flex hone to fit a pin bush? I don't like the idea of using a little stone type brake hone, as most are too coarse (made for doing ferrous cylinders) and perhaps too violent on bronze. Its easy enough to get a 1" aluminum oxide flex / ball hone (brake / lifter size) of a nice grit (240/320?), and I can't see why if carefully done, I can't carefully take off a thou or 2 as required.

In al these years building motors, I have never had to ream/hone a pin bush before, (lucky me). But it seems easy enough as long as you take it easy, check your measurements often, and maintain alignment & lubrication etc.

I seen videos of engine shops sizing rod eyes using a chucking reamer and lots of lube. Just running the rod eye in and out (by hand) until its at spec. So can a well lubricated, nice new flex / ball hone be any worse? Or was that "shop" a bit amateurish?

Happy for any views...

Thanks

[blykins]

I think you'll have trouble keeping it straight and round with a ball hone. 

[mungus]

I think you'll have trouble keeping it straight and round with a ball hone.

Thanks for the reply Brent. Yes I had that concern initially, after seeing a YouTube "expert" using flex hones freehand to do this job on diesel pin bushings.

My plan was to have the hone in my pillar drill and set the con rod up dead square in my compound vice. That way it should be dead straight and running at an exact RPM. Being a new hone it will be as round as a flex hone can be??? :-)

A straight 31/32" chucking reamer, is about the same price as a new BRM flex hone, but as the clevite pin bushing is a split design, I think a spiral would be safer. Unfortunately they are also much dearer... I felt a flex hone is less likely to "bite" and ruin the bushing, if I do anything wrong.

May I ask what methods you have heard of shops using? Is there a piece of gear specifically for this job? Or is it just a chucking reamer and lots of lube etc. Just curious...

[blykins]

Most shops have a "rod shop" to do this kind of work.  Usually a mandrel with an adjustable hone that's set to a mic, then checked on the included bore gauge.  It's the same fixture that you use to hone piston wrist pin bores.  Needs to be very rigid and straight.

[SMorton67FB]

I would take it to someone with a Sunnen hone or something like that. Some non automotive machine shops could have one and could do it. You may be able to get it yourself but without a rod checking fixture you wont know if you got it straight or not. I would think a master cylinder hone would be better than a ball hone.

[mungus]

While I've been here tonight (OZ time) I've been googling and found a bunch of second hand Sunnen (and other brands) rod machines for sale. $400-$1000 AUD second hand. So that's how they do it...
Its definitely a proper set up.
 

[pbf777]

     

So my question is this. Has anyone used a flex hone to fit a pin bush?

     No! this will not work!         Well, depending on how concerned one is with "proper", and yes, it has been practiced by others in the past, just with say very unreliable results.     

     I don't know how much material is needed to be removed in the I.D. but "Flex-Hone" type devises are only useful in deburring and perhaps a surface texture treatment intention, not the removal of any real some of material with any specific dimensional concern.

     Also, and particularly with split bushing inserts, an expanding type mandrill needs to be utilized to "expand" and swage the bushing in tightly, generally the parting line will disappear after this process, this prior to the honing to a finished size, even sloppily holding within .0002" of the intention.     

     Scott.

[runthatjunk]

Do it once and do it right. (That does NOT involve a ball hone).

[475fetoploader]

Tobin-Arp