© Copyright 2007 - 2017, Coachworks
we offer camshaft gears!
We are committed to helping you get a gear that ACTUALLY FITS!
After 35 or so years of building engines for these wonderful machines, and
after having amassed a collection of around 30 lose camshaft gears - many brand
new - I was working on an engine where I tried every single camshaft gear on
hand and NONE of them fit that engine, not even close!
After pondering this, I realized two vital details:
1) In all these decades of engine building, I've never needed a larger
gear, only "smaller ones". So, naturally, what gets left over
are the larger gears. I called many other engine builders and we all have
had the same basic experience: your best bet is to put the one that came out
back in, and failing that, you'll probably need a smaller size! And;
2) The markings on the gears are worthless. I took all the gears on
hand and rank-ordered them by size, and sure enough, I had brand new
minus fours (-4) that were larger than used plus ones (+1)! This is
not supposed to be! And, note that absent markings that actually reflect the
real size of a gear, it means that gears have to be selected by trial-fitting
(Note, by the way, that gears aren't measured by the diameter of the outside
of the teeth - like threaded fasteners are - but rather by the contact face
where two gears mesh. So, it's harder to measure than most people realize.)
What to do about it? You COULD begin manufacturing of new gears, but for one
engine, that seems rather silly. Or, you could cut a large gear into a smaller
one! AH, but if you do that, exactly what size do you cut your gear to - given,
mind you, that you don't yet know what size you need?
Why, you need a whole collection of gears, ranked by size,
then trial-fit them until you pick the right one!
And so that's exactly what we've done and now we're offering the benefits to
Here's our deal when you buy a gear from us...
- Try your original core and tell us the results of your attempted fit as
outlined below: if it rocks out when you turn it backwards, it's too tight,
and the closer it is to staying put, the closer it is to fitting. If it doesn't
rock out, is there any lash? Can you hear a click when you wiggle it in reversing
directions? Find complete directions below.
- Send us your core along with the results of your attempt to fit it.
- We'll send you a gear that's an estimate based on your results from following
the procedure outlined below.
- You then try the gear we've sent you - how well does it fit?
- If the gear we send you doesn't fit to your satisfaction, return it us,
in the same condition as we sent it, along with your new results of trial-fitting,
and we will send you another one. All the shipping is on you, of course. If
our smallest gear is still too big, we'll cut one down for you. And, if our
biggest one is too big, you may have to wait a while for a big enough core
to come in, or we'll refund your money - but we highly doubt that will ever
happen! We will repeat this process until either you get one that fits to
your satisfaction or we run out of gears to try and refund your money.
Please note that there were many different manufacturers of these gears. Some
have bores for dowel pins and some don't. Some are magnesium and some aluminum.
Nearly none are perfect in all regards. Many of our gears are new, but we're
not promising new, only helping find a good fit on a gear that's runable. And,
the gear on the crankshaft matters, too - YOUR "crank gear" - it may
not be round! It may have burrs on it, etc.; its flaws can appear to be flaws
with the camshaft gear. With regard to our exchange service, we are only concerned
about size ("fit"); you may or may not get a gear with dowel pin holes
- if you request it, we can try to find you a gear with dowels, but that's
not really a part of our service (you can have a machine shop add dowel pin
bores for you - but they need your camshaft to do it). Further, because we
have no control over the crank gear or the camshaft to which the gear is fitted,
we offer NO GUARANTEES whatsoever of any kind, only that we'll keep swapping
out gears for you when you pay all the shipping and keep returning to us the
same gear in the same condition that we sent you - as described here.
How To Fit A Cam Gear
Camshaft gear fit depends on many factors, but here's a straightforward procedure
to figuring out the fit of any particular gear pair in any particular crankcase.
- The crankshaft gear must be inspected for burrs or "dents", and
any found must be either removed or a better gear selected - this is best
done before the gear is mounted to the crankshaft.
- The crankshaft gear must be installed properly onto the crankshaft, with
all the details that entails.
- The crankshaft itself must be properly fitted to the crankcase with all
the details that entails.
- The camshaft's gear mounting surface must be clean, flat on the threaded
surface, and the outer rim where the gear mounts must be round, and both concentric
and perpendicular to the camshaft axis.
- The camshaft gear must be mounted to the camshaft with the timing mark on
the gear perimeter (usually it's a dot, but sometimes it's a line) directly
in line with the oil pump drive slot, and the bolts tightened to 18 foot lbs.
The bolts should be "grade 10" (marked 10K), or grade "10.9"
(marked 10.9), and just long enough to go all the way through the camshaft's
mounting flange and not more. Any other bolts should be rejected. For trial
fitting purposes, no thread locking should be used - that can (and should)
be added after gear fit is confirmed.
- Both gears must be perfectly clean and dry with no shavings, oil, or dirt
of any kind in or on either gear - a small nylon-bristle brush can be helpful.
In the following discussion, we need to discuss what "size" means.
...In doing our research, no specific reference could be found as to what a
"zero" camshaft gear's effective (tooth-contact) diameter is, nor
did we find any specific reference as to what the "step" is between
sizes. And, we proved via actual observation that today the size markings
on gears are useless because they no longer relate - if they ever did - to actual
gear size probably, at least in part, because they were made on different tooling
at different times. (Unfortunately, saying "a plus two (+2) gear is just
barely too tight" is meaningless because the +2 marking is relative only
to the tools that made it.)
What IS useful, though, is a relative measure (which is what the original markings
were all about - they just aren't useful today). We presumed that the gap between
the official sizes was defined as equal to the official tolerance in lash such
that if you just barely have too little lash, you need the next smaller gear,
for example. We then measured all OUR gears. So, when you send us YOUR gear
AND tell us your trial-fit results, based on the following, we have a pretty
good idea which gear you might need because we're going to measure YOUR gear
on the same tooling as we measured ours!
- Engine assembly is traditionally started with the installation of parts
into the LEFT case half - so, we presume use of the left half here.
- There are two dots on the crankshaft gear - one on either of two adjacent
teeth - and one dot on one tooth of the camshaft gear; the gears are meshed
with the one dot on the camshaft gear going between the two dots on the crankshaft
gear. Rotate the crankshaft so the two dots on the crankshaft gear are just
above the horizontal (case seam).
- Align the cam gear to mesh with the crankshaft gear and lay the camshaft
into its bearing bores, gently - wiggle it as necessary to confirm it's seating
in its bores as best it can - DO NOT FORCE IT.
- If the camshaft won't lay flat into its bores reasonably well, the gear
fit is perhaps five sizes too big or more - that's a guess.
- If the camshaft appears to lay flat in its bores, rotate the crankshaft
counterclockwise, so the gear mesh is going "up", away from the
crankcase half. Here's how to interpret the results:
- If it rises up right away, the gear mesh is perhaps four or more sizes
- If it makes it up to half a rotation or so before rising up, it's maybe
three sizes too big.
- If it makes it close to a full revolution, it's maybe two sizes too
- If it makes it a full revolution but not three revolutions, it's one
to two sizes too big.
- If it doesn't want to walk out, congratulations, you MIGHT have a good
gear fit! Now... do you hear a "click" when you rock it back
and forth (clockwise / counter-clockwise)?
- NO! - It's perhaps one size too big - MAYBE. The official clearance
(lash) is 0.0006" to 0.0016", and you may not get an audible
click with the tight-end of that range. Many engine builders will
just go with a "it doesn't walk out" fit, trusting that
the clearance actually grows as the engine warms.
- Yes? YAY, your gear is probably a perfect fit! If it doesn't click
all the way around, it means one of the two gears aren't true-running,
which could be caused by problems with either gear, either shaft,
the mounting of either gear or a multiple of these, and it's a judgment
call whether or not to run with it, as noted in the "NO!"
- "HEY, there's a LOT of clearance!" - Exactly how much
clearance is hard to determine without special tools, but the amount
of rotation the cam gear can move is a good indicator. If you can
put a dial indicator on a cam tooth as perpendicular as you can, that
information would be useful in finding a better fit.
Please note that these estimates of how far off any given camshaft gear is
from a correct fit for any given case, crank, cam, and crankshaft gear, are
just that; estimates. The purpose of this is to help you inform us about how
good (or bad) your present cam fit is so we can more easily help you find
the right gear for your engine.