Triumphrat

Tig66208 · 09-10-2007, 12:27 PM

With the help of my uncle, split the cases of my TR6R this weekend. Glad I did, the main bearings were shot and there were a couple small pieces of crap boucing around the crankcase.

From removing the heads a couple weeks ago, I already knew that someone had installed heavy-duty valve springs and titanium tops. However, upon splitting the cases, I found some Megacycle Cams! Now it's just a matter of trying to determine which ones....

Had a question though, trying to identify the pistons (+ .40). Can't find a name on the inside of the skirt, but the closest thing to an identifier is a symbol that best I can tell, looks like a "home plate" type shape with an AE in it. Any ideas?

Mecchanica · 09-11-2007, 03:29 AM

You have British made pistons, the AE is the same company as Hepolite. The question is........what is the bore? AE also made pistons for the Morgo big bore kits which have 76 millimeter bores as standard. If you have forty over standard pistons, they should be about 72mm bore. If they are forty over Morgo kit, they should be about 77 millimeters.
Megacycle cams are usually marked, if not, then measure the height of the cam lobe and subtract the measurement taken at ninety degrees to that, across the base circle. The remainder is the cam lift. Compare that to their list of cam profiles. The most common was the 51065 in street bikes. Go to their website to get the data for their cams. Or call Marino Perna at MAP in Florida and he can answer your questions. Tell him Kim from Hawaii sent you.

Tig66208 · 09-11-2007, 10:39 AM

Thanks for the info on the pistons. I don't believe it's the big bore kit - the jugs are standard 650 as far as I can tell. I'm going to measure them like you said and see what I get...I'll post a pic too.

I measured the cams in the way you mentioned, and came up with .374". Megacycle has a .375" cam, 510-x2. Seems pretty racy, but I do have the racing valve springs, however flywheel is unmodified, and I'm pretty sure these hepolite pistons don't qualify as racing! I will probably contact the person you have mentioned. I'd like to be sure as to what I have to make sure this engine goes back together as it should.

Thanks!

Mecchanica · 09-12-2007, 02:06 AM

Yikes, that is one hot cam. Dumb to fit them with stock pistons. The long overlap bleeds a lot of compression out of the cylinder during low speed running, which is why cammy engines are lumpy at idle and need to have a higher idle speed....So higher compression pistons bring it up to where it runs. It would be pretty hard to start, I would think. Stock cam lift is .314", duration is 270 degrees.

I would look for some good stock cams or those 51065 Megacycle if you want to use the stock pistons. Stock cams run very well. I would bet that you have STD radius (.750") tappets, if you fit stock cams and would like more low and midrange and less cam and tappet wear, run them. If you want stock specs, get some R radius (1.125") tappets.

What year is you engine again?

Tig66208 · 09-12-2007, 10:59 AM

It's a 72 TR6R. I need to double check with a micrometer...but yeah, interesting that they weren't using high compression pistons. My uncle that I bought the bike from (and he bought it this way) said it always started well and ran nice. He sees no problem leaving it as is, and I generally trust his judgement. He'd built a LOT of NICE Triumphs and Matchlesses.