Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board conrod bushings

Alrighty...another probably silly question. What, in your experience, is the easiest and most efficient way for a shadetree mechanic to replace the bushings in the small end of the conrods? Heat and tap the old out with the new? This is my first motor rebuild and I just don't wanna make no stupid mistakes, so pardon the seemingly silly questions. Thanks

i use the new bushing to push the old one out with a small peice of threaded rod and two sockets but then it usally needs to be reamed to the proper clearances that means you need a ajustable reamer as well just saw one on evilbay the guy who owned it liked it a lot more then me $$++++ hth aprophet aka david

Greg: You have an opportunity of a lifetime to learn something and meet new and interesting people.

Before we offer the new rod bushing we should explore whether the rod truly has the "potential" you expressed. This is going to be your only chance to check this rod, before the next rebuild, to see if it is worthy of your trust.

We are going to do this by removing the bearing shells, replacing the rod cap and torque the rod cap bolts to factory specifications. What we are going to do is check to see if the big end eye has gone oval.

Now my limit for an aluminum rod is .001" if I am going to use the motor "in anger," I have no practical limit I use for the street, but .0015" or so seems reasonable. A third the diameter of a human hair doesn't seem like a lot, but to that ALUMINUM connecting rod it is the only warning it will ever give you that has been abused and READY TO FAIL. While it seems drastic, if the rod doesn't pass this test the next tool I use is the hack saw. The life of the person riding something I built is worth more than the price of a connecting rod.

So with the best measuring tools at hand I set out to measure the rod to see if the big end eye has gone oval. Now you are not going to find these tools in most shadetree garages, but the right tools are common in automobile machine shops.

Only then would I start the process of replacing the rod bushing. Oh, the same guy who confirmed that your rod was round has the equipment to install and hone the bushing so that it is round, parallel to the big end, and the proper .00075" clearance. Something that you will not be able to do with your adjustable reamer.

Ok, there can be a problem... you find that the big end of your aluminum rod is out of round indicating that it has started to FAIL. The local machinists, who should know better (it's amazing what people will do when there is a payment due on the Bass boat), offers to "grind" the cap and resize the big end. Now this is standard practice with STEEL rods, but a recipe for disaster with an ALUMINUM rod. It erases the one clue that the rod is failing and its appointment with destiny and the hack saw.
john

Greg -
I was going to say exactly what John said, but dang it, he beat me to it!

Suffice it to say that on a Brit bike, MOST of an engine rebuild is simply measuring ALL the wear surfaces. It is NOT as some infer, simply replacing a couple of bearings and bushings and then painting the cylinder. This ain't no Chevy or Honda.

In truth a lot of the bearings and bushing may NOT need replacing. It may turn out to be far more important to replace the stretched rods and a scored oil pump rather than the mains. And some of those bushings (i.e. cam bushings) might almost fall out... while installing the new ones may take 2 PHds and a full machine shop.

And all this has to be done in a sterile environment using the same care it takes to build an aircraft engine. Believe me, it just looks easy.

:bigt:


PS. One of the items to measure on a 1966 is the height of the cam lobes. I believe the number is 1.125" outside (base circle to lobe). Didn't see that one in the book did you?

Ok...did I miss something or was only one of the three respondants working on the right end of the rod??

relicduke,

I noted with amusement Healy's response; he must have read Greg's post too quickly, or has had a recent scare with connecting rods. Good advice as always, just not the ansswer to the question posed.

I've always replaced wristpin bushings in the same way as aprophet. Don't forget to redrill the oil hole!

relicduke and lostboy
Heally did, in fact answer the question.
I will attempt to translate:
Figuring that Greg is new to Triumph re-builds, John wants him to do it the most correct, workmanlike, and long-lasting way. There is no good way to do that in the back yard.
John said: take the rods to a machinist. Have him first check that the big end is round. If not, destroy them. Then have HIM install the bushings and hone to clearance while making sure the bore is parallel to the big end.
Having the wrist pins exactly parallel to the crankshaft has to make a happier, cooler-running engine.
Now, if you weren't planning to take the bottom-end apart, that could be a problem.

The backyard method will, of course, usually work, depending on your definition of "work", and I have used it even with "pre-honed" bushings that usually give the correct slip-fit after being pressed-in. You can then see that the wrist-pins meet each-other by slipping them together with another bushing between. If it all fits and seems right, then I think it is.

John's way is to do it in a manner that all bases are covered and a very long-lasting rebuild results.

Maybe I don't even need to replace the bushings, maybe not even the bearings. The motor was(according to my Dad)running fine the last time it was run, which was in the '70's. I disassembled the engine primarily to clean it up, then thought,I'm in here, may as well replace it regardless of how good it looks. The big end shells are visibly flawless, no scratches or scoring whatsoever, the main bearings looked good and spun freely with no slack, but I'm this far and really don't intend to go here again no time soon, so I'll replace them. It's not like I'm trying to ressurect the dead...just a little preventative medicine.Heck...the sludge tube wasn't even all that bad...maybe a bottle cap full of gunk!

If there is less than .001 clearance on the small end, IMHO let it be.
Just curious, how many miles on engine?

I honestly don't know....no odometer...heck no speedo for that matter!!!

:bigt:

I recently rebuilt a 1974 TR5T 500cc engine that had suffered rod failure. Fortunately the cases were unscathed. A NOS crank cost $225.00 plus freight, NOS connecting rods another $200 plus freight, and I got a deal on those. Main bearings add another $150 or so. A gasket kit, bore job on replacement cylinder as original left liner fell prey to the broken rod..... I have A BUNCH of money in this bottom end. Take the rods and crank to someone who knows these things and have them checked out! You have not likely had a broken rod saw a set of cases in half while spewing shrapnel and hot oil on your legs, or locking the rear wheel at 65 MPH.... trust me you do not want to have these things happen to you.

Forget what was when the bike was last ridden, take Mr. Healy's advice and CHECK IT WHILE APART! As the ad says... "you can pay me now, or pay me (or the emergency room) later".

Amen Brother!

A broken rod with a head of steam up will likely also bend both cams, been there and it is not a happy place.

i love the saying it looks good!!geez wish i could see .001 out of round.listen to what john and rf have to offer.they have been building these bombs for along time.when the big bang happens its ugly.the newest of these is at a min. 30 yrs old,the more owners the machine has indured the worse they usally are.spend the money with a known brit bike guru and do it right or buy a new modern triumph and just go riding.if you dont know who mr healy is find out! this forum is vey lucky to have him take the time to spend helping keep is passion for these bikes going

Man, I'm glad I've never been afraid to tear into something and learn about it myself.

I don't get all these doomsday predictions, What are you trying to get this guy to do?? He's already said there's almost no wear on any bearings and almost no sludge in the crank, yet his engine is likely to EXPLODE.

Why are we motorcyclists? Certainly not because we are afraid of everything. Has anyone gotten caught on a crowded Interstate lately? Now that's a death threat.

The cautions presented here are not predictions of doom, just reminders to check everything while the engine is apart. I am sorry if my reply was a bit over dramatic, but for the minimal additional expense and time invested now a future adventure in accident avoidance might be prevented. Peace of mind is priceless, and in this case affordable as well!