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Rocker arm ratios

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pacerman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Topic: Rocker arm ratios
    Posted: Mar/29/2015 at 3:29pm
I have a factory rebuilt 1972 short block 232 with a bridged rocker 1976 head on it.   Cam lobe lift (from the TSM) on the 72 engine is stated as .254 inches.   Cam lobe lift on the 1976 engine is specified as .232 inches. Since I don't know the valve lift in either case, was there a difference between the ratio of the shaft rockers for 1972 and the bridged rockers on my 1976 head? Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amc67rogue Quote  Post ReplyReply Direct Link To This Post Posted: Mar/29/2015 at 3:45pm
Shaft rockers were 1.5 ,bridge rockers were 1.6.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Mar/29/2015 at 9:52pm
Originally posted by amc67rogue amc67rogue wrote:

Shaft rockers were 1.5 ,bridge rockers were 1.6.
They revised the cam to match the rockers. The idea was to keep things the same at the valve despite the change in the rockers.

.254" * 1.5 = .381" valve lift

.232" * 1.6 = .371" valve lift

The later cam also had a little more duration: 259* to 254*

Basically the same for all intensive purposes once the rocker ratio is factored in.

NOTE!!! The .232 lift later style cam is no longer supported. Any stock replacement cam you get from Melling or Federal Mogul (Sealed Power) will be the earlier .254 lift cam. When used on a later engine this will result in a valve lift of .406". Stock valve springs will be fine, but check them and make sure they meet or exceed factory spec. I'd recommend buying new springs. Sealed Power stock replacement springs will be fine since they slightly beat the stock springs.

Just went through the above scenario on my later 232.

Edited by FSJunkie - Mar/29/2015 at 10:08pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Mar/29/2015 at 11:21pm
Taking this a step further, simply because I had no clue! hae a 1977 TSM and a 1974 TSM along with a 1970 which I did not look at.
I just finished installing an Iskenderian 270HL cam in my 1974 232 engine with the shaft for the rockers.
I never really looked up the rocker arm ratio's on the. The is my second Iskenderian cam install on an AMC I-6. the first was a 256 Super cam in a (I believe) 1976 engine pulled from a pacer for use in my 1980
Spirit and it had bridged rockers. So I assume the shaft was used at least through 1974 and maybe changed to bridged rockers in 1975 or 6 and I guess it was never an issue so I never needed to know.
But the cam spec's for 1977 gave different cam lift and duration numbers depending if it was a 1bbl (Carter Yf) vs a 2bbl (Carter BBD) carburetor. Who would have known, or I guess really cared.
However my Iskenderian Catalog lists the rocker ratio as 1.6:1 for all 6 cylinder, 199-232-258 engines. Which I guess now can be assumed to be incorrect.
But they are not the only ones, my Comp Cam catalog lists lift information for 1.6:1 rocker assemblies under the category of 199-258 cu inches. However, my MOPAR catalog does not even mention them.
So I guess the watch word is:
Go figure.
My 232 should still run pretty good when I get around to getting it in something.
I did find out that the inexpensive chrome steel valve cover I have used on a number of late 258's does not fit a rocker shaft engine. But my Clifford valve cover does and will.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Wrambler Quote  Post ReplyReply Direct Link To This Post Posted: Mar/30/2015 at 9:12am
I had a el cheapo Chrome on my Shaft head, strange, I always thought they were one cover sold by a bunch of places.

IIRC, the engines were shaft till around 71ish, then bridged, then back to shaft for 74 because of patent or other issue. Once that was resolved they went back to the bridged rockers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Mar/30/2015 at 12:48pm
I've always wanted to build a performance version of an AMC 232 I-6 and I bought this one when it showed up as a low mileage rebuild taken from a Gremlin. I stashed it in 2004 and let it sit until recently and opened it up to discover it had a shaft in it. The thought of a short stroke 6 after building 3 long stroke ones, a 225 and 2 258's always appealed to me. Having a shaft to keep the rockers in place was pure bonus, so I thought.
Now it is going back together and I need to find something to put it in.
I can put it on a 904 or a 5 speed, either way it could be a lot of fun.

I have used a number of these particular chrome valve covers purchased from a variety of places. Actually most of them came from some one who could not get them on their engine. They are made in China and this one the owner actually thought it was an OEM part. Why? I don't know. Kennedy was selling them for a while and may still be. There are three holes in them for oil hole, PVC and what ever. The same size as the GM rubber plug used for Oil Caps in the Vega's and other engines.
The sheet metal for the breather bottoms out on the shaft.


Edited by uncljohn - Mar/30/2015 at 12:53pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2015 at 5:11pm
Originally posted by FSJunkie FSJunkie wrote:

   When used on a later engine this will result in a valve lift of .406". Stock valve springs will be fine, but check them and make sure they meet or exceed factory spec. I'd recommend buying new springs. Sealed Power stock replacement springs will be fine since they slightly beat the stock springs.


The basic rule of thumb I have used on installing cams in AMC engines built since 1966 has been that a valve lift of less than .500 lift is a direct bolt in using OEM Valve train components.

As those are the lift ranges I have stayed with in over the years, I have yet to have a problem with them.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2015 at 8:37pm
I like overkill and extra margin.
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