3 bearing cams in a 3.0L?

[andrew15]

Can I use my 3-bearing cams and towers in my '80 3.0 rebuild (w/ 10.5:1 JE pistons)? Right now I have a great set of early 'S' cams in my 2.2 S, but will stump up for a cam regrind on my 4-bearing ones if I have to...

Regards,
Andrew M

[Eagledriver]

I don't see any reason why you couldn't do this. You could even use your old rockers and rocker arms since they are used to the cams.

-Andy

[Henry Schmidt]

Three journal cams have a smaller base circle so when they a put in a 3.0 or larger engine you end up with very little valve adjustment left. In other words you need to screw the adjuster in too far and that leaves very little screw for the nut to tighten on. Will it work? yes Is it nice? no

[andrew15]

Thanks Henry - Done deal, the 4-bearing cams will go out for service. Is this something you guys do?

Regards,
Andrew M

[Henry Schmidt]

John Dougherty is the best source of cams and cam info I know.
Search - camgrinder - on this forum.

[914timo]

Three journal cams have a smaller base circle so when they a put in a 3.0 or larger engine you end up with very little valve adjustment left.

This is something I didnīt notice when I put my three journal Solex cams to my 3.0. There is still lot of adjustment screw left. How much the base circle is smaller in the old cams ??

[camgrinder]

Timo, The difference at the valve stem tip is about 1.6 mm.
The base circle on the 49mm cams is 32.00 mm +/- and the
early 47mm cams is 29.45 mm +/_.

Henry, Thanks for referring me!

[914timo]

1,6 mm is about 1 and half rotation in adjustment screw. Now I donīt wonder any more why I didnīt notice that.

Next question is, where is this 1,6mm lost in in three cam journal engines ?? Or, do they have 1,6mm longer adjustment screws ?? Or, have they 1,6mm longer valves ?? I donīt understand ......

[andrew15]

I believe that it's shorter valves x the rocker ratio.

Regards,
Andrew M

[914timo]

Rockers.....I donīt think so. They should be the same from 2.0s to 3.2s. So are valve adjusting screws. And valve springs. But, 3.0s and 3.2s have different valves than 2,7s. Could the answer be there ??

[914timo]

And how about valve lash caps. Could I and should I correct the geometry with 1,6mm thick valve lash caps ??

[Henry Schmidt]

I have seen lash caps used for this correction. You can buy Porsche lash caps ($19.00ea the last time I bought them) or you can seek out an Alfa mechanic and get lash for a mid 70's GTV ? at 1/4 the price.

[914timo]

Thanks Henry !!!! Very nice information. I have to think about that.

Thanks again

[Henry Schmidt]

Originally posted by 914timo
1,6 mm is about 1 and half rotation in adjustment screw. Now I donīt wonder any more why I didnīt notice that.

Next question is, where is this 1,6mm lost in in three cam journal engines ?? Or, do they have 1,6mm longer adjustment screws ?? Or, have they 1,6mm longer valves ?? I donīt understand ......

1.6 mm is the difference in base circle on the cam. In order to calculate the difference at the valve you must also add rocker ration. On a standard cast 911 rocker the ratio is about 1.4 to 1.
The factory compensated for the base circle change by shortening the valve stems on the engines that had 49 mm vs 46 mm intakes.
The stem change is as fallows.
46 mm intake = 114 mm 49 mm = 110.1 +or - 4 mm change
40 mm exhaust = 113.5 41.5 mm = 108.4 5.1 mm change

Still think it's only a turn and a half difference? And we must also consider the rocker geometry change.

[914timo]

Ok, the later valves are shorter. That was interesting. Thanks for the info again. I have to think about doing something to that problem. Maybe lash caps or 4 bearing cams....