I found a box of six Gotha 1.6-ratio cast iron rockers, new. a little
surface rust that a quickie dip in Coca Cola would probably take right
off. The box says "INTAKES ONLY". They're from 1961 or so. I assume, but
wanted to check, these will still leave plenty of clearance between valves
and pistons with P4120243 MP 244/244/28/.436 camshaft and no head mill?
Good idea on the street, or maybe leave 'em in box and admire 'em instead? What is the effect of increasing the rocker arm ratio?

redbear@vrx.net

Dan,

Assuming you have a 225 with stock comp height and head mill (or within 0.100" of stock even), you will have absolutely no trouble with valve-piston clearance with that cam. You will be going from 0.436" lift to 0.465" lift using those rockers, which will still leave you probably 3/8" of v-p clearance (wayyy more than the 0.090" required). You will also get slightly more duration, around 5 deg or less.

I don't know why they would only work on intake. You might try them on int and exh, since a lot of cams are ground with more lift and duration on the exh side.

Have fun,

Lou

Good. I looked at the box again, and it actually says "HIGH LIFT" without a specific ratio. I don't know where the 1.6 came from. I guess it was just a guess. It's probably a reasonably decent one; you couldn't go too much more than that and still maintain proper valvetrain geometry. They did not come with tappet clearance adjustors, so I guess (hope?) the originals fit. The six rockers are in a plastic bowl of Coca Cola (convenient, cheap phosphoric acid solution) to get the surface rust off.
:
: I don't know why they would only work on
: intake. You might try them on int and exh,
: since a lot of cams are ground with more
: lift and duration on the exh side.

I would, but I have only six of them! Are you sure about that on the cams? My recollection is that the '60-'64 and '65-'70 cams had a few degrees more duration and lift on the intake side than on the exhaust side. Example, '65-'70 cam, 240° intake duration, 236° exhaust. I might be crossed-up here, I bet Doug knows.

--DS
: Have fun,
:
: Lou


redbear@vrx.net

Just discovered that unlike stocker rockers, there is no oil hole at the valve stem end of the rocker arm. I guess this means oil won't be dripping down onto the valve stem area. I have good (positive I *think*, maybe regular umbrella) valve stem seals, so I can't imagine this is a problem, but...is it?

redbear@vrx.net

I am under the thinking that a SL6 would like more lift on the intake valve.(more flow without the reversion effect the longer duration will introduce)
Here is a chart on SL6 cams to review, the factory did put less duration on the exhaust side but I do not know why. Does anyone know?
DD

Also, wouldn't a higher-ratio ("high lift") rocker arm increase the opening and closing rates, which I recall as being important?
:
: factory did put less duration on the exhaust
: side but I do not know why. Does anyone
: know?

I've often wondered not only why they did that (difference in valve sizes intake/exhaust??) but also why they *stopped* doing it with the '71 cam. Looks like installing the high-lift rockers on the intakes would get back to that "dual pattern" (terminology?) arrangement used by the factory in the earlier cams, but with the longer duration and higher lift of the later cam. In *theory*, I guess it should run pretty well, eh!


redbear@vrx.net

Well, the oiling at the valve stem end is so the valve stem tip won't wear so much. You'd probably have to do a lot more valve adjustments (at the very least) if you put those rockers on unless you found a way to drill a hole to oil the valve stem ends.

i think the basic theory on the exhaust lift is that the exiting gas will be a lower density than the intake charge which also explains the smaller valve on the exhaust side. dual pattern cams tend to make good power and run fairly smooth. the 340 faactory cams had a higher lift/duration on the exhaust to give them that "rumpety-rump!" sound. ahh, thank you mr. marketing man!

-james

ludite13@cs.com