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RE: [T3] My Square's engine... what to do?

On 16 May 2006 at 10:26, Keith Park wrote:

> I don't think the FI engines are any harder on valves than a carbbed one
> would be, that doenst make sense but a valve job on ANY AC engine at about
> 60K (miles) is recommended, even the T4 engines.  

I agree that the FI is probably no harder on engines than carbs. The FI engines 
I've had have had very good life, and I let most of my valve jobs go at least 
100 kmiles.  

> I think another important factor is how well the valve train geometry is set
> up, Im not sure how much that would have varied from engine to engine from
> the factory but in rebuilds it probably does.  That has a HUGE effect on
> guide wear. 

I tried to model this a few years ago and worked thru a math problem to let me 
try to optimize the valve train geometry. It turned out to the be quite a 
difficult problem, but the geometry I finally came up with was within my 
ability to measure the stock geometry. As valve seats are ground, however, the 
valves recede into the head and this changes the geometry, so shimming the 
rocker stands is necessary to compensate for this. Adding swivel-foot rocker 
adjusters changes this a bit more and requires more shims.

In the end I have to shim the heads a bit and shorten the pushrods to make 
everything work out right, but the end result has worked well for me so far.

Note that changing the valve springs or the valve lift would require a new 
calculation and a different optimum geometry. I've only done this for stock 

Note also that the intake and exhaust valves are different lengths. This is 
important, because it allows the optimum position for the rocker shaft to be 
the same for all the valves, even though the lifts are different.

Jim Adney
Madison, WI 53711-3054

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