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Discussion Starter #1
I have recently had oversize exhaust valves from IAP fitted to my 85 Spider graduate.
The problem I am now having is that I cannot get valve shims small enough to set the clearances.
Looking on IAP the smallest valve shim is 51thou and I need down to 33thou.
Can anyone advise of where I can get special shims?
Or some other way of achieving the valve clearances?

Thanks
Drew.
 

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As far as I know, the only way to get into the correct range is to renew the valve seats. It is obvious that they now are cut too deep. I would not grind the shim pads and do not let anyone tip grind the valve stems, as then the pads will interfere with the keepers. Regards Ian
 

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Discussion Starter #3
Ian,
Thanks,
I was rapidly coming to that conclusion and planning on talking to the engineering shop tomorrow.
Thanks again.
Stupid question: Are replacement valve seats generic or individual to the car/engine/head?
Drew
 

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I have recently had oversize exhaust valves from IAP fitted to my 85 Spider graduate.
The problem I am now having is that I cannot get valve shims small enough to set the clearances.
Looking on IAP the smallest valve shim is 51thou and I need down to 33thou.
Can anyone advise of where I can get special shims?
Or some other way of achieving the valve clearances?

Thanks
Drew.
Valve seats are not generic. You will need to use valve seats that fit the Alfa 2ltr head. I'm not sure what seats will work with the oversize valves, as the seat angle needs to be changed as well as the diameter opened up for the larger valve size. (I have to admit I've always just told my head man Steve what I wanted and he "did it") so hopefully someone on the BB can add on here what seats you need to use, and the source. I'm of the thought that stock seats will put you right back to where you are now.

I hope this helps, George
 

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Discussion Starter #5
IAP sell the oversize valve with the statement that the valves can be used with the standard seats just recut the angle.
Has anybody used them and had the same problems as me?
Thanks for the info.
Cheers
Drew.
 

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Now might be the time to think about different camshafts, ones with a slightly smaller base circle. Not the ideal solution to recessed valve seats but it may be a viable option.

Regards,
Don
 

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Now might be the time to think about different camshafts, ones with a slightly smaller base circle. Not the ideal solution to recessed valve seats but it may be a viable option.
Richard Jemison has pointed out on more than one occasion that grinding the base circle is usually a bad idea because it increases overlap and thereby reduces low end torque.
 

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I would say the valve stem tips need to be ground if all else is right.
 

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I would say the valve stem tips need to be ground if all else is right.
RADAMM: cutting down the tip of the valve stem will, as has been pointed out above, cause the shim to wear on the valve keeper and cause the valve to become "unglued".

What you suggest will be a band-aid. The correct solution is to installing thicker seats.
 

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Richard Jemison
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Valve issue

All of the oversize valves have too much stem above the keeper(collets) groove. They should be fitted and the excess removed prior to final assembly.
Why did you use oversize valves? They only reduce flow. And did you think about weight?
Seats are only 46mm OD. When cut to max opening a minimum of 1mm seat width is required. Thats 2 mm from the OD:confused: Any valve larger than 44mm is only obstruction to flow.

But you thought big valves mean better flow HUH. :rolleyes: Did you pay more? Bet he`s happy to sell you the "Hot Ticket" Bet you got the 3 angle seat as well. Don`t expect performance increases.

Thicker seats don`t work... you want seats hanging down in the combustion chamber?

Only fix is to quit listening to the crap on the BB.

Cams can be made to smaller base circles with no real issues, Cheaper to remove valves, reduce length over groove, and while you are at it,cut down the valves OD as well....Still heavy and thick but what the heck...
 

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Discussion Starter #11
Wow!
Here was I thinking that engineering was a precise science!
With so much opinion being voiced, it seem that the laws of physics are optional or at least discretional!

Thanks for all of the rhetoric, it is very entertaining.

WRT the valves, they are 41mm valves and IAP state "dyno proven to increase HP upto 7%" granted that could be .1%.
I may be naive, but felt that a BB endorsed supplier would at least be reputable.

Can you confrm that oversize valves routinely have the stem length above groove, adjusted to match the particular application?

Thanks again
Cheers
Drew.
 

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Valve stem height, as Richard points out, is one of the last measurements taken and adjusted in a valve job. It should have been done prior to final install of the springs and keepers. Obviously, interference with the keepers by the shims has to be kept in mind but won't occur when "all else is right".
 

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Richard has a lot of experience, don't just ignore it. But at least in my case, I've had strongly held (and stated) engineering ideas that were just wrong - or at least incomplete.

Several people have done some careful flow bench work on Alfa heads; from their reports, sometimes bigger valves do improve flow; it mostly depends on just how the intake path (mostly) and piston (a bit) are shaped. It also depends on what's upstream of the valve - carbs are different than injection ports, throttle bodies, etc. It even depends a little on how smooth the path is (polished ports?) and how well the gaskets fit. Just changing the valve usually doesn't do much but cost $$ and create problems.

An important point is that Alfa engineers were ahead of their time in what they put in production. These heads are pretty good in stock form, and it is not easy to make improvements. It's not like hot-rodding a 1960's 327 Chev block, which can be improved with a hand-file. It's possible to more than double the flow of some engines, but getting 20% from an Alfa head is extremely hard. We Alfisti do not have a lot of "bolt-on" horsepower; it was already designed in.

Consider the Twin-Spark. This new-generation engine has a much narrower valve angle (between intake and exhaust) and a flatter combustion chamber. THe narrow angle makes the intake path straighter so it flows better, and the chamber shape makes the flame front during ignition more precisely controlled. It took a complete re-engineering to get a 20% improvement. (Top end 2L Nord engines can reach 185 - 200 HP, TS can top 220+).

Robert
 

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Discussion Starter #15
Robert,
Thanks,
I have no intention of ignoring anybodies advice, it is all great info.
I am relatively new to Alfa ownership and all of this is most useful.
I was also being serious that it is very entertaining!

Cheers
Drew.
 
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