Valve Train Geometry, Now with Pics! To shim or not to shim... That is the question. Options

[yeahmag]

I've got Jakes (nla) econo swivels and have all ready decked my rockers by .060". It looks like I have very close to ideal geometry with the adjuster run all the way in. Should I remove another .010-.020" off the rocker to gain adjustment back or change the shims out for thicker ones?

-Aaron
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[mike373]

Yes..... I just went through this myself. Start with the smallest shim. This will raise the pivit point and allow you to bring the swivel out another turn. Also check the adjuster angle against a straight edge on the top of the valve keeper. I posted a pic in a recent thread.

Mike

[yeahmag]

Thanks. I all ready have the shims that came with the kit in there... I'm not sitting in front of them, but they look about .060". So you think I should go up to say an .080" shim?

-Aaron

[mike373]

I ended up using a .020 shim. The thinist one that came in the rocker shim kit that I got from aircooled.net

[davep]

I thought Jake was saying that in most cases (95%) you don't need to shim the rockers. He implied that shims are a last resort to correct other faults.

[yeahmag]

I'm not sure what does and does *not* apply to the "budget" adjusters. He does ship them with a shim and I simply don't see a way to not add more shim and have correct geometry without cutting the rocker arms back quite a bit more.

-Aaron

[Twystd1]

Does this engine have a stock cam?

And are you using stock pushrods...?????

Clayton

[brer]

So how does a .001" difference in the beginning of the pushrod travel affect total movement at all?


Same axis
Same total pushrod travel
Adjusters to compensate for slack

Are the arcs really that different?


(IMG:style_emoticons/default/mellow.gif)

[yeahmag]

One of Jakes cam's - I'm using an adjustable pushrod to set the geometry.

-Aaron

[Twystd1]

Kewl.

I saw that you posted to Jakes site as well.

I think someone said a picture tells a thousand words. (IMG:style_emoticons/default/beerchug.gif)

Clayton

[mike373]

.001 difference in pushrod length.... and multiply by the rocker ratio..

[Joe Owensby]

If you have an adjustable pushrod, and are checking the valve geometry, you can very easily see how sensitive the actual valve travel is to the length of the pushrod . Once you get it tuned in properly, record the total travel. Then, just make a small change to the rod length, and then see what difference in total valve travel you get. When I was working on my geometry, I used a digital camera to kept a listing of the total travel for each adjustment in rod length, by using a card with the total lift on it and the rocker arm position at half lift both in the picture. This also allowed me to remember the angularity of the rocker arm at center lift position. Unfortunately, I did not keep these, so I can't go back and tell you what variation I had with minor changes.

I am no expert race car engine builder, but on mine, there was a sweet spot where minor changes in the pushrod length made very little change in the valve travel. Jake raby had a good article on his web site. It would have been so much better if it had photos. If you make the pushrod a little shorter or longer, you will still adjust the valve gap to 0.006" or whatever your settings are when you do the final assembly. So, if the rod is a few thousanths short, it doesn't necessarly mean you will lose that much in valve travel. While you have the hardware to measure the length, perhaps you could do the test and let us know how sensitive it is.
I had some concerns about the swivel being too close to the as received originally releived rocker arm. I was also concerned about the relatively short length of thread left in the rocker arm if it were to be releived more. I was told to releive it some more. Here is where a photo would have been good for peace of mind.

[yeahmag]

OK... Here come the pictures.

Zero Lift:


Half Lift - 1


Half Lift - 2

[yeahmag]

...and full lift

[yeahmag]

BTW - I measured the shims to be .065". -Aaron

[brer]

If you have an adjustable pushrod handy I'd be keen to see exactly how much difference say .003" in pushrod would translate into half and full lift numbers.

Its not as simple as multiplying by rocker ratio from how I look at it.
.
.
.
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But then again I have always preferred arcs to straight lines
and 3's over 4's .



Edit: OH! are you saying you installed a .065 shim in between 1st and second measurement?

[yeahmag]

brer,

Those were just slightly different angles. I've used the shim pack supplied by Jake the entire time. I've measured them at roughly .065". I can get an exact measurement on them if anyone likes...

-Aaron

[mike373]

Hey YeahMag....

I hope you didn't make all your measurements without having both rockers on the shaft, and without the solid rocker spacers between them. (as your pics show) The rockers will have side to side movement and give poor results.

[orange914]

Hey YeahMag....

I hope you didn't make all your measurements without having both rockers on the shaft, and without the solid rocker spacers between them. (as your pics show) The rockers will have side to side movement and give poor results.

good eye, mike. i've been seeing your post on jakes site, seems there are quite a few of us building these at approx. the same stages-lot to learn-! i just hope i can get jake to respond to me for a cam as his sight wont let me log on to order, just to the forum. besides i need a few items that arent listed.

yeahmag keep the pictures coming! a picture is worth 1000 words

mike

[yeahmag]

Made the measurements with the spacer kit installed but found that with two washers/shims it was way too tight. With one washer/shim and the spacer I have .010" of play. Do I grind the spacer, rocker stands, or find thinner washers/shims?