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1974 SPIDER WITH WEBER CONVERSION.

Camshafts are of unknown origin (no markings except for "306" on intake and "300" on exhaust). Best guess is Alquanti. Lobes measure 11.1mm.
Current clearances are intake=.006 and exhaust=.008"
IAP tech said DO NOT run engine with those clearances because as the engine heats up I'll end up with no clearance and valves will not close.
Braden's book says "Under any circumstance, .012 is the minimum clearance for any valve. Has anyone heard of clearances as tight as .006 and .008 on any cam?
 

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I have clearances of .008/.012 for my RJ136/785 cams. These are as advised by the designer of the cams. Yours may be similar if they are a modern design.
 

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Current clearances are intake=.006 and exhaust=.008"
IAP tech said DO NOT run engine with those clearances because as the engine heats up I'll end up with no clearance and valves will not close.
alfaparticle said:
I have clearances of .008/.012 for my RJ136/785 cams. These are as advised by the designer of the cams. Yours may be similar if they are a modern design.
I'm not taking sides here, but those two statements seem contradictory. If the IAP tech is correct, then the clearances tighten up by .006 - .008" once the engine is fully warmed up (anyone agree or disagree?). That wouldn't change whether your cams were of a modern design or older design.

Note that valve clearances of .006 - .008" are about 1/3 of the stock clearances (.019" I, .021" E).
 

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Richard Jemison
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Clearances

Alfa Romeo factory valve clearances are only for stock cams.

They are not going to "close up" as perhaps pushrod motors might have done.

Aftermarket cams are not built with excessive seating ramps as with stock cams.

I suggest .008 to .010 for the intake and .010 to .012 exhaust.
 

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But Mad North-Northwest
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Indeed, I was always told that overhead valve clearances actually open up when hot. I can't prove this, though.
 

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Indeed, I was always told that overhead valve clearances actually open up when hot. I can't prove this, though.
That is also my understanding. If the camshaft, the valve and the head around the cam journals rise to the same average temperature then the gap will widen because aluminum has a higher coefficient of thermal expansion than steel.
 

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Trained (ex)Professional, , 1953-2018 RIP,
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That's exactly right!

The valve clearances will increase about .003" when the engine is hot.
 

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If the camshaft, the valve and the head around the cam journals rise to the same average temperature then the gap will widen because aluminum has a higher coefficient of thermal expansion than steel.
The problem is they don't rise to the same temperature, except when not running
 

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I believe tighter clearances increase the overlap and you lose power at the top end as a result. I have mine set to .019 intake and .021 exhaust per the service manual and she pulls like a Banshee right up to redline. I have the 11.1 mm performance cams from Centerline with over size intake valves and Borgo 10.5:1 pistons. There was no literature with these cams indicating that clearances should be set differently than with stock cams. I had to do some work to prevent interference with the tappet bores but that was explained in the instructions. Also checked piston to valve clearance with a piece of solder - not a lot of leeway there. Been running them this way for about 50,000 miles and just did a clearance check about 6 months ago - no change.

So the clearances being discussed here sound awful tight to me. Does anyone have anything in writing to back this up or is it all just hear-say?
 

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In the UK I always read that 0.50 inlet and 0.55 exhaust for 11.1 cams was good...millimeters that is!..which is basically what kcabpilot has his set his to.
Colombo & Barriani (C&B) show these gaps on their website, scroll to "Vecchi Modelli" (older models!), even though they do not show exactly a 11.1mm lift cam. But even their full race is given as 0.40 IN and 0.50 EX:
Colombo & Bariani: alberi a camme dal 1934
 

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The cam manufacturer will specify the clearances. If you don't know what cams you have then you must guess the clearances. If you set big clearances and they make a lot of noise then you probably should tighten them up some. I mistakenly set Richard's cams to .016/.018 when I first got them and they made a racket.

Richard has designed his cams for the clearances that he has stated and I have repeated. If Kentjw has modern high performance cams then they are likely to be similar to Richard's. C&B cams for 4 cylinder Alfas are old designs that use bigger clearances.
 

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Where does the idea that it's supposed to be "quiet" come from? There's nothing in the maintenance documentation saying you should tighten up your valve clearances until it idles like a Lexus. I'm just asking where you guys are getting these numbers from, it seems like you're just picking them out of a hat and calling it good.

I'll just say I've got over half a million miles in the various 4 cylinder Alfas I've owned - never had a burnt valve, damaged cam or tappet and have never found it necessary to make any adjustments to valve clearances between engine overhauls.
 

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valve clearances

I have Shankle 7L cams in my '78 Alfetta GTV. The camshaft # provided is 5417. The valve clearances recommended by Shankle are .006 for intake and .008 for exhaust. I have the original sheet in my hand. Recommended intake timing is specified as opens 38 deg BTDC, closes 62 deg ABDC, and lobe center 102 ATDC. Exhaust timing opens 61 deg BBDC, closes 37 deg ATDC, with lobe center 102 deg BTDC. I have run .006 and .008 for many years with very good results, and clearances never change from one check to another. The car has Euro headers and is otherwise stock. Dave Strus, Kokomo, Indiana.
 

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kcabpilot,, ' quite' very smooth..i guess it's just trail and error, to some people, i try mine at alfa setting... noisey, so tryed at diff. settings.. found on my car 0.15 on each side works well.. never burnt a valve myself..
 

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Richard Jemison
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Misinformation

#11 (permalink) Today, 01:53 PM
kcabpilot
Registered User Join Date: May 2003
Location: Antioch CA
Posts: 589

I believe tighter clearances increase the overlap and you lose power at the top end as a result.
No, more overlap improves higher RPM. Less improvers lower end.

I doubt you have pitted your "banshee" against a motor with exceptional cams!:p
 

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Probably not Richard but I sure have fun with it.

So why does overlap help at upper end? I'd have thought it was the other way around but that was just a guess on my part. Also, do you think it's okay to tighten up the clearances on stock cams as bianchi has (no ill effects). I see Dave has documentation calling out much tighter clearances but then that's a totally different cam from what I have as far as when the valves open and close.
 

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Also, do you think it's okay to tighten up the clearances on stock cams as bianchi has (no ill effects).
Hey, that's a good question! If clearances don't decrease with temperature (apparently they increase), then why can't we run .006" I - .008" E clearances with any cams? That is .013" tighter than stock (.019" I - .021" E), or about .33 mm. So wouldn't that turn a 10 mm cam into the equivalent of a 10.33 mm cam?

Or is there something in the profile of earlier generation cams that requires a larger clearance?
 
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