Valve Clearance for 2.5ltr for Track use

3210 Views 10 Replies 8 Participants Last post by superloaf, Apr 1, 2011

Razz

Discussion Starter · Mar 22, 2011

I use my Milano for lapping events. I set the valve clearance to OEM specifications. When the car gets hot, I start to hear the valves knocking.

Intake 0.019”
Exhaust 0.009”

Did anybody try to run a different clearance than OEM for track use?

No mod. to my engine, all is stock.

Thank you.

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Brendan_LS

· #2 · Mar 24, 2011

what weight of oil? maybe the oil temps are getting up there and the film is breaking down...

oil temps over about 110°C (230°F) are not unusual on warm days, but if its staying past 115°C for long periods, look into a thermostatically controlled external cooler, or try moving up to a 60 weight oil (or a good synthetic).

the factory alfa v6 clearances are just about on par with most other engines with adjustable rocker arms, so they should be fine...

my 2 cents tho...others may have other theories

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PSk

· #3 · Mar 24, 2011

A tap is better than a burnt valve.

Note also that valve clearances are critical for valve timing ...
Pete

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Alfar7

· #4 · Mar 24, 2011

Clearance

If you are running stock Alfa factory cams of any source, Verde/164 etc.) you can close lash on intake to .017 and exhaust to .007.
Seating ramps on factory cams require adequate clearance.

Aftermarket cams will typically be noisy due to lack of "closing ramps" even when set to .010 intake and .005 exhaust.

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Razz

Discussion Starter · #5 · Mar 24, 2011

Thank you All,

I’m using 20W50, I was told by a reputable oil company rep. not to use synthetic in old engines, I was skeptical when he told me. I always use synthetic, even in my lawnmower, snow blower etc… This year I will try a good synthetic oil.

Any recommendations? My engine is stock, no mods.

Orazio

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racingswim2006

· #6 · Mar 24, 2011

Perhaps this is a good opportunity to clear this up....

But I thought you wanted to be at the high end on cold valve clearance/lash if your engine will be running very hot or if you're doing extended lap sessions or endurance race?

Do the valve gaps not close (and approach zero) as the engine warms up to operating temp on an engine? Or is Richard merely suggesting that the factory clearances can be excessive even for track use?

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ghnl

· #7 · Mar 24, 2011

Valve clearances will change a little as the engine goes through temperature changes. I have checked both cold & hot and the difference is usually very slight. I have not measured the clearances partly warmed up - that is when they would likely show some measureable difference.

The clearances Richard mentions are vital to keep the cam/valve interface on a designed in 'ramp' on the camshaft lobe. This ramp allows the cam to slowly (relatively speaking) come into contact with the valve/tappet. If adjusted outside of the designed ramp range the valves will be slammed open/shut.

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Gubi

· #8 · Mar 24, 2011

I was always told the valve clearances actually open up a bit when the engine is hot, though I'm perfectly happy to be corrected on the subject.

Valve noise would be more of a "tick" than a "knock" I'd think. Not to scare you or anything, but the phrase "knocking when hot" makes me think bottom end noise.

If it's more of a "tick", it could also be something like a leaking exhaust header. Mine were loose at one point and it made a hell of a racket when the engine was hot.

Just speculating here.

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superloaf

· #9 · Mar 30, 2011

As far as the oil to use, the 944 turbo guys on rennlist have had problems with modern oils because of the lack of zinc. Very few oils still have zinc which coats the metal and protects in situations where the oil film disappears as in high shear situations (not sure if my explanation is correct but you can google it for the proper description.) Anyways, I have switched from Mobil 1 to valvoline racing oil just for this reason.

See here:
Valvoline.com > FAQs > Motor Oil > Racing Oil

I've heard recently that mobil 1 has added zinc to some of its oils but not positive about that. I like the VR1 oil because it comes in both regular and synthetic also.

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Razz

Discussion Starter · #10 · Apr 1, 2011

I was checking the size of the shims for my intake valve and all my tappets have this grey line around. This is the first time I see this. Is it normal for an Alfa Engine? All 6 are the same.

I also have another question, I know my way around engines but this is the first time adjusting valves this way with shims. For example, the clearance I need is 0.017" (0.432 mm) my actual measurement is 0.022" (0.559 mm). my actual shim measurement is 2.260 mm. in order to achieve the desired clearance, I would need to add to the shim 0.127 mm. Total measurement of shim needed is 2.387. not sure I can get 2.387, so what is better:
2.375 or 2.400 ?

Thank you for your help.
Orazio

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superloaf

· #11 · Apr 1, 2011

When I rebuilt my engine, the tappets had similar markings.
Also, a trick told to me by an alfa shop is that you can file down the thicker shim to make the actual size that you need. I just used some fine grit sandpaper and it worked fine.

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