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Discussion Starter #1
Hey everyone, harley guy here, new to triumphs and the forum so please excuse my ignorance at some things. I rescued a neglected 1970 T100R chopper from a guy in town that unfortunately had some rod bearing issues once I drained the oil and I'm in the middle of a rebuild. Was checking the cams today and while the lobes look great my clearance on the bushing side is in question. My micrometer grew legs I guess so I'm working with a dial indicator, both cams are measuring .807 (manual calls .810) but both bushings are measuring .810, manual calls for .001-.0025 clearance on the bushing end. My understanding is the reamer is .8125. So do I run it like it is and call .003 close enough on clearance or do buy new/used cams and ream current bushings to .8125 or install new and ream? Someone had been in the motor before so I'm not sure what has or has not been done to it right or wrong. Not sure if this is a place where it pays to be anal retentive or if a buck can be saved here. Thank you all in advance! Attached is a pic of the bike from Christmas since I didnt have room for a tree...clearly I'm a bachelor lol. Thanks, Christian
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Discussion Starter #2
Looking at the numbers with a fresh set of eyes it looks like everything is roughly .003 under what it should be...calipers are probably off, gonna go grab a new mic today and hope that's the issue. Still leaves me with .003 clearance though. If the cam spec is .810/.8105 and the reamers being sold are .8125 that would leave you at the top end of the clearance tolerance range with new bushings so maybe I'm okay?
 

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If your camshaft ends definitely are 3 thou under that suggests that the wear may have gone beyond the original case hardened depth, in which case further use will cause more rapid wear. You are correct in that the the working size of the bush is 0.8125/0.8135 when fitted and reamed, and this would give a working fit of 2 to 3.5 thou, depending on manufactured tolerances of the camshaft. If you choose to use the camshafts anyway, as the basic unreamed bushes will tend to close up slightly when pressed in, you could see what size you get without reaming them; it may give you a better working fit on the worn camshaft bearings. (Note: use a scraper to remove any slight distortion on the outer edge of the bush from where it's been pressed in, otherwise you may not get the camshaft to go into the bore to try the fit.)

Edit:
You could also try a metric 20.6mm reamer (these are available on eBay, etc). This equates to an imperial size of 0.811" - a bit tight but may suit you camshaft if you still need reaming of the new bushes.
 

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Discussion Starter #4
Thank you for the reply. Its good to know that everyone who is installing new bushings is in the upper end of clearance the tolerance, as my clearance is falling in that area too .003. Since all my measurements seem to be undersized but my bushing clearance and lobe lift is still spot on, and those are the difference between two measurements so the consistent inaccuracy wouldnt matter, I'm really leaning toward calipers not being accurate anymore. I'm running into town later to grab new micrometer to verify.
 

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In case you missed the edit to my post:
You could also try a metric 20.6mm reamer (these are available on eBay, etc). This equates to an imperial size of 0.811" - a bit tight but may suit your camshaft if you still need reaming of the new bushes.
 

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Remember that your cam bushings will need to be line reamed with the cases assembled not just reamed to size.

Rod
 

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Rod,
Unlike the B range models line reaming of camshaft bushes is not applicable to the C range 500 engine. This only has bushes in the drive side casing; the timing side casing has no bushes and the larger camshaft ends run directly in the bores in the case. This allows the cams to be removable from the timing side without splitting the engine cases.
Cheers,
Brian
 
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