Posted by: caryandjohn | July 12, 2014

Rebuilding the Tiger …

I’ve been chasing charging issues with my wonderful 1973 Triumph Tiger 750 for a long time …

Had to put three stators in the bike in the last few years …

My friend Ricky Pharr of Kustom Culture Motors finally figured out that the Tiger has been trying to tell us that the main bearings that support the crank are worn out …

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Result? Total tear down … 😦

I didn’t recognize the Tiger in the shop …

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Master mechanic Ricky …

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The damaged rotor, which hangs off the end of the crank … scored where it came into contact with the stator …

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The crank and connecting rods …

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The five-speed transmission … this engine is know as a “unit” engine, with the transmission included in the same case as the crank …

Pre-unit engines have a separate transmission case that can be unbolted and removed without disturbing the crank case and vice versa … the pink stuff is the transmission lubricant which is still separate from the engine oil that lubricates the crank … in Japanese bikes the trans and crank are all in engine oil …

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The timing side of the unit engine case … you can see the transmission case with its pink lube, and get a sense where the crank sits behind it …

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Valve and timing covers …

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The head, which contains the intake and exhaust valves and their springs …

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The worn out exhaust port that the exhaust pipe slips into … these will be sleeved so that new pipes can slide in and fit properly again … rattling over the years damaged the fit …

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I took the head, crank, cylinders, pistons and the primary cover to visit master machinist Mike Crowther of Engine Dynamics in Petaluma …

Mike used to work on my EX500 race bikes in the ’90s, and now works on my KLRs … he’s very familiar with old Triumphs …

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The pistons, looking good, with their worn out rings …

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… and a couple of pics of the cylinders … this is a worn out cylinder with a set of once-over bored pistons I had put in about eight years ago … Mike will bore and hone the cylinder for another set of pistons just a bit bigger than the old ones …

Mike agreed with Ricky that the main bearings are worn out … Ricky said he measured a thousandth of an inch run-out in the big roller bearing that sop ports one side of the crank and eight thousands of an inch run-out in the rotor … run-out is the up and down motion of a rotating object, like an unbalanced tire running down the highway … enough movement in my engine to bring things into contact that shouldn’t touch … as evidenced by the damaged rotor in the pics above …

Mike said that the main bearings in these unit Triumph engines are notorious for wearing out, as are the engines … “Good for 25,000 miles,” he says …

Mike pronounced my crank and valves good, and sent the crank home with me … Ricky will have a friend inspect the crank’s run-out before it is re-installed …

I need to get Mike new pistons and head pipes, and we’ll be making progress …

I’ve ridden this bike a lot since I got it years ago, doing many high mile-multi-day rides every year … it has proved to be a forgiving bike for a vintage bike newbie … so I’m happy to give it some love and a new lease on life …

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9/8/14: Progress … got the new pistons and bored cylinders and fixed primary adjusted plug on the primary cover back from Mike at EdCo and dropped off with Ricky at Kustom Culture … the head has a new valve job … Ricky steam cleaned the frame and can now start re-assembling the engine …

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Responses

  1. How great to have the experience to diagnose the problem and the skill to fix it– Bill S.

  2. That’s for sure!


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