Hi All.
Weeks behind on the list, as usual. On the plus side, the project "Khartu"
is progressing. But I digress. Or is that regress.
Anyway...
Cam bearings: if the cam holes are out of round... you have no choice but
to align bore the block for the Spitfire bearings. Unless you want to
replace the block, that is. ;-) This is tough to measure when the block is
in the car, so many people overlook this step.
Cam hardness: Cams should be hardened in some manner after the regrind.
They should also be treated with a material to aid in the proper break-in.
Some folks are doing more now. In fact, Piper Cams just told me to
cryogenically treat my cams. I'm going to do it, as I figure spending $100
now (for the cam, lifters and springs to be treated) is worth it more than
speding $300 plus to replace the cam/lifters/springs etc. if/when a lobe
wears out. I'll report to the list if I find anything earth shattering.
Cam followers: replace these with the cam.
Cam springs: don't go too insane on the seat pressure. Unless you want to
keep replacing valve seats. Or if your lift is higher than .410 or so at
the valve. Then you have to deal with super springs. Especially if the lift
is over .450.
Cam profiles: The 17/35 numbers sounded a little wierd to me. So I looked
at Egil Kvaleberg's web site for tuning Triumph 2.0 and 2.5 in-line 6's,
and sure enough - these would be _way off_. Now if you told me 35/71, that
I'd believe. Although that would be a "lumpy cam" at idle, coming in
somewhere around 290 or so of duration. The TR5 cam is 35/65 - and that's
280 duration and does produce a bit of a lumpy idle. And this is probably
the cam you folks are referring to as the TR250 cam...
I will point out that the TR250 cam is probably the "lamest" TR6 cam as the
lift is only .330 at the valve... I'll also point out that that cam,
Triumph part number 307621, is the same cam used up to the '74 model year,
which used the 311399 cam. A whopping .340 lift at the valve. The PI cams,
307689 and 311399 appear to have .360 and .340 lift at the valve,
respectively. So, the PI cam for the TR5 is the cam to get... if you're
playing that game. The TR5 cam is also the wildest duration at 280 degrees.
This is getting into the "lumpy" zone.
Break-in: This is _THE_ most important step of a cam install. Make sure
that you get the motor start _right away_ and get it to run above 2000 RPMs
for at least 20 minutes when you get the motor started... and you must lube
the heck out of the cam and lifters when you assemble, or you can kiss the
cam goodbye.
Pushrods: a lot of folks have problems dialing in the initial adjustment
because the stock pushrods are too short... get the tubular rods from Ted
S. or TRF and then make a jig like the Comp Prep book tells you to measure
the rod length... if you cannot do this, take the whole schmeel to a real
machinist and have them do it. Your valve guides, pushrods, rocker arm
assemblies etc. will all thankyou with longer service if you do not skip
this step. If anyone cares why this matters on a case-by-case manner, I'd
be glad to explain, but suffice to say: the base circle for two cams with
the same finished profile can be markedly different. As such, the length of
the pushrods will be different. Maybe by a lot. As an example, I have two
cams in my basement, both with .403 lift. The base circle on one is
something like 1.040 or so. The other's base circle is .950 or so. That's
almost 1/10 th of an inch difference. You can bet that the same size
pushrods won't work with these guys.
Cam Cores: I don't know if anyone is making new blanks, but Piper will only
grind a grindable cores, and those seem to be getting rare. But that might
because people like me wind up with 4 or 5 bad cams while we're looking for
a good core. Oh and those cams that we screwed up because we didn't follow
the break-in or had other problems... And most of the regrinders don't like
to weld on new lobes... this suggests to me that they have quality control
issues with regards to keeping the "repaired" lobes on the cams, but I have
no actual evidence of this.
Now, you can get regrinds all the way up to over .485 lift with you stock
cam. If you do that, and you keep the duration on the mildish side (under
290, for sure and under 280 is better) then you'll make gobs of torque and
have a smooth idle. However, keep in mind that if you go to big lift, you
have to play with the springs so the lifter doesn't "bounce" of the cam
shaft. This is where a lot of folks get in to trouble when putting a cam in
the car. And it also means grinding the valve spring pockets to make sure
the springs don't bind... don't skip this step!!!
Now, my unsolicited opinion is: It's not real easy to just change the cam.
Sure the physical change is pretty simple, but you really need to think
about what you are doing when you play with the cam, as all sorts of
"issues" crop up. Just talk to someone who's changed the cam in the same
engine a few times to get an idea of the potential frustrations.
Just for laughs, look at the cam profiles at the following URL:
www.ashford-perf.com
And don't forget Egil's web site... good stuff there.
Now back to your regularly scheduled programs...
rml
TR6's
=====================================================================
Bob Lang | TR 6 Guy | Editor: New England Triumphs
Phone: | 617-253-7438 (days)| 781-438-2568 (eves)
Occupation: | ComputerZ | TR fixer-Upper
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