[TR] Opening Up Connecting Rod Oil Passages

Reihing, Randall S. Randall.Reihing at utoledo.edu
Sun Dec 4 08:23:29 MST 2016

No matter how the passages are cleaned out and opened up, patience and a light touch is key. Assuming the oil passages are in straight lines, I would suggest initially foregoing any powered attempts to clean out those passages using tools that are as highly tempered and hardened as drill bits, etc.  An extended length 4-6 flute reamer with straight flutes, favored over tapered reamers for this application, available from any machine tool supply house or catalogs like McMaster-Carr might be a better choice than a drill. I would prefer a series of extended length straight flute reamers in this application. Reamers are not designed to pull themselves deeper into the material they are used in, but rather to enlarge an existing opening. Once the passage has opened, a reamer will be very effective at removing rust, corrosion and even original material but far less likely to break than a drill bit. If a drill bit is used, extra long aircraft drill bits are available from the above sources and can be mounted in a hand held drill chuck and applied by hand, reducing the chance of breaking but even in that method I would not use a drill bit if the passage were open. I would still much prefer using 2-3 reamers of various diameters close to each other in O.D. starting with one close to the same rough diameter of the existing passage and carefully work up from there. Patience and a light touch is key.

Once those rods have their oil passages cleaned out it might be worthwhile talking them to a motor rebuilding shop to have them properly evaluated for wear and condition. A well equipped shop will have a dedicated machine to test and evaluate each rod in addition to using hand micrometers to measure each rod end opening. This way each rod can be checked for length being within accepted tolerance plus any indication of very slight twist and/or angle deformity that might not be visible to the naked eye.

I did this with a Ford V6 engine I recently totally overhauled starting with a bare block and a new crankshaft and discovered two of the original 6 rods were outside their tolerance range in at least one of their specifications. Unless you have a lot of experience using precision ID and OD micrometers and have a granite plate it might be worth your time to have a dedicated, well equipped, engine rebuilding business check each rod for you. The last thing you want to end up with is an assembled engine that has a slightly misaligned rod or one out of wear tolerance, inside.

Good luck on the rebuild.

Randall S.

From: Triumphs [triumphs-bounces at autox.team.net] on behalf of Alex&Janet Thomson [aljlthomson at charter.net]
Sent: Sunday, December 04, 2016 9:18 AM
To: 'Bill Brewer'; triumphs at autox.team.net
Subject: Re: [TR] Opening Up Connecting Rod Oil Passages

If I were to use a drill, I think I would try a slightly undersize bit. Rust usually breaks up fairly easily but removing original material might be a lot to ask a full size, generic bit to do at such a length. I would dread the thought of a drill bit breaking of in the hole. I think there would be less chance of breakage with a slightly undersize drill.

Alex Thomson
From: Triumphs [mailto:triumphs-bounces at autox.team.net] On Behalf Of Bill Brewer
Sent: Saturday, December 03, 2016 9:48 PM
To: triumphs at autox.team.net
Subject: [TR] Opening Up Connecting Rod Oil Passages

     So I am rebuilding a Standard Vanguard engine for a 1953 Morgan Plus 4. The connecting rods have been laying on a shed floor for decades. They cleaned up nicely, but the oiling hole through the connecting rod to the small end bushings were all rusted solid. I made a tool out of a piece of 1/8 brass welding rod. I pounded the end flat, like a screwdriver, and pounded it in while turning with a small Vise-grips. It got the hole opened and rust poured out. The hole is about 0.180” diameter. I’ve been trying to find a long 3/16ths tube brush (like a pipe cleaner) to clean them out better, but no one makes one long enough. The brush needs to be about 5” long and the longest that McMaster Carr has is 3”. I could pull the small end bushings out and go at it from both ends, but the bushings in there fit the wrist pins perfectly and I would rather not mess them up if I can help it.
     I have been considering buying a 12” long 3/16ths (.188”) drill bit and running that through. It might open up the hole a little bit, which might not be a bad thing.


     Has anybody else been here? How did you get by this?

     Bill Brewer
     Tehachapi, CA

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