1967/1969 Bonnie Rebuild Desert Sled Project - Any Advice

on the tappets, the R is ground to a 1 1/8-inch radius, and the standard to 3/4-inch. they give different durations and accelleration as a result, so you should have all of the same kind. i have read that the T120 came with R tappets 1966 -on.

are you keeping the cams? what do the lobes look like? in a perfect world you would not put a different tappet onto a lobe that had worn-in to a previous one. but people do it all the time and i suggest you get hold of an R intake tappet to replace that standard one.

if you end up buying new cams you can have the tappets refaced. i think the standard cut is 0.010, or at least thats what ionce measured onsome

 

look at tbe cam journals. are they scored, pitted, or flaking? same test on the cam lobes, as well as uneven wear. youre looking for depatures from smooth, even wear.

on the tappet faces, look for the same problems. does any metal look smeared?

you can measure the cams to see if theyre worn unevenly, but as far as i know there are no specs about absolute wear. someone else may have something to say.

balancing is more of an art than a science, in my opinion. youre doing more than eveni g out weights. by adding or removing metal to the crankshaft itself you can change the direction of the vibration, and how severe it is, to some degree. i didnt balance my morgo when i installed it, and im happy with it. i did have my race crank balanced, and it vibrates ludicrously at idle but smooths out at speed. sort of.

 

https://www.jrcengineering.com/technical-support/jrc-conrods/

found some info on the JRC rods

 

Triumphs twins over the years all used various balancing percentages to smooth out the riding experience and it was down which worked best with the frame design at the time, on 650 units they arrived at 85%. Personally i never balance cranks unless asked as they will all vibrate somewhere in the rev range. I always use new rods and bolts when building a engine but if asked by the customer to use the old rods i recommend new bolts, i also de nib/bur old rods and polish them.

 

use new bolts. the bolts have a finite life because each time they are torqued they stretch a bit and then return when undone. but never quite all the way.

eventually you will have a bolt that stretches a bit too easily. when correctly tightened up it will still stretch under load and loosen. then it can unscrew or allow the bearing clearance to grow with a resulting failure.

i dont use a torque wrench on rod bolts. i measure bolt length with a micrometer and use a fixture with a dial indicator to tighten them to a pre-determined stretch. once their relaxed length is a certain amount over their original length-- 0.005 inches for my ARP bolts-- the manufactuter recommends replacing them.

i dont do that. i blew up a record setting motor at 131mph because i had re-used thr rod bolts. four bolts cost about US$80, but now i use them one time and then just throw them away. i suspect rod bolts are one of the most highly stressed components in the engine, and one of the most expensive if they fail.

 

rod bolts are cheap, considering









you can also make an argument that old aluminum rods should be replaced, as darkman said earlier. aluminum rods have a finite number of stress cycles before they fail. if the rod has been wrung-out to a high rpm or abused, then the number of cycles is decreased. with an old machine, you never know how close the rods are to failure until you measure, and the only way to do that is to take em out and measure the big end concentricity.

steel rods do not suffer this limit. something like the MAP steel rods will happily last forever in your machine, unless you neglect the rod bolts like i did. there are other rods available, but these are commonly used in highly-stressed race motors here in the states:

http://www.mapcycle.com/categories/...p7061-triumph-t120-6-5-h-beam-4340-steel.html

 

thats my 650 race bike. one rod bolt unscrewed and i blew the motor between the mile and the mile and a half.

lost the rods, pistons, cylinders, two valves and two guides. was able to save the crank and the head. robbed some crankcases from another machine, transferred everything over, and im still running the bike.

but rods and rod bolts are a major blow up when they fail. i dont risk it anymore. not worth it.

 

Its common practice for some engine tuners/manufactures to mix and match R and non R lifters to achieve desired lift/duration and not an issue as even Triumph ended up deleting the exhaust oil feed on later engines with the advent of better materials/metal treatment being used, I block the front tappet feed on all engines i build these days. At this stage it would be best to grind or replace your tappets/lifters and the cases shape wise all differ over the years but all factory cases have matching numbers stamped on the lower frame bolt lugs.

 

what did you use to get the tappet blocks out with? theres a tool for that

 

Its only some aftermarket cam makers that spec R for both inlet and exhaust on unit 650's so use what your cam maker specifies with your current cams. Don't concern your self about the oiling as even i block off the feed to the front lifter block with standard cams just as Triumph did with later engines. If you decide to go with standard cams 70-9989 ex and 70-3134 in cams are best overall for street use with R inlet and non R ex.

 

you dont need the tappet oil feed with your megacycle cams. did ypu mark the orientation front and back when you took the tappets out?