MTFCA Forum

RE: viewtopic.php?f=5&t=51850&sid=1bfc58e08 ... 518d237cf9

There is an interesting post in the Classifieds, and since myself, Steve, and a few others kinda hijacked John's ad, maybe it would be best to continue our discussions here.

So my next questions are; -in looking at pictures of Brad's (-and other's Boring Bar), it appears that the Engine Block's Cam bores become the 'datum' for aligning the reamer to the rear Bushing centerline ( ℄ ). Wouldn't using the bored Babbitt Bearing surface of the actual repoured Cam Bearing be the proper way to locate the Reamer? My point is that if either of the Front Cam Bearings or Center one was bored slightly off-center in the shells, ...even being off 3°-5°from parallel with the ℄ of the Block's cam bores, align-boring that Bushing is going to be for nothing because the Camshaft will still be bent somewhat when it is installed.

Off center boring of new (repop) cam bearings was an issue. Also consider wear in the block. Original cam bearings wear the same foot print unless you make your own from a piece of billet cast iron. I gave up on repop & poorly rebabbited cam bearings long ago. Since then I have searched & found NOS & very good used bearings.

I think I get the reason for the line reaming tool. Not to align the bushing necessarily, but to assure the reamer cuts perfectly parallel.
I have done a back door kind of procedure for reaming/fitting a replacement bronze bushing. I will bore the new bushing in a lathe to square it up & size the bored hole smaller to compensate for the "stick's" clearance + the shrinkage of the press. No reaming after installation. (I didn't have or know about this neat reamer guide) Cam always slides right in with no indication of a slight misalignment.

Brent

you're question/approach would be technically ideal to make use of a faulty part, but you are now trying to drive an existing hole (in the bushing) to one slight offset or another, using a bar whose small diameter has the stiffness of a noodle. The chamfer of the reamer will be the driving force in the setup and will simply seek to follow the existing bore of the bushing regardless of where the faulty squishy babbit is trying to aim it.

I made my reamer such that it takes shell reamers fit to a male Morse taper on the end. With 1 foot long steel handles fitted with steel balls on the end like an old time machine tool (2" long end-to-end), the momentum of it being spun by hand is immense and plows through the bushing very nicely.

I made precision sleeves for the bearing holes that reduced the reamer shaft size just a little bit, and used a pre-ground straight shaft for the tool. I decided that making the male Morse taper seemed easier than boring a hole for a straight shank reamer or a female Morse taper. The shell mill came from MSC. The whole fabrication was easy and straight-forward.

FWIW - it's been a long long time since I've done this job but I seem to recall that I had to bore my new bearings to size (?)

I wonder if the Factory fitment of the cast iron bush was align reamed after fitting. The photo of such a tool in the wanted ad indicates it may have been.
I do as john does. Bore the new bronze bush to fit the shaft and press it home. Rarely does it need any further attention, that can be done with an adjustable reamer.

Allan from down under.

A few comments: 1) If you are reaming the rear bushing to compensate for a front or center cam bearing bored off center, that's just plain bad practice. Replace the bearings or adjust your method of boring them to get them concentric with the OD. Reaming them to size in a bench vise is a good way to get them off center. They should always be bored in a lathe to size.
2) in 45 plus years of building these things, I have actually found a block where the rear cam bore in the block was off center about .010. Only a single instance, but..... had to probe the bore with gage pins against the cam and make an eccentric rear bushing- and yes, the cam was straight and the front and center bearings were snug in the block.

Reaming tools were available back in the day. Mine uses the front and center block bores to center up on. The portion doing the cutting is a tapered bore shell reamer. I seldom use it, but always check the alignment when sliding the cam into position. Hope this helps!