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Old 11-03-2005, 15:20   #1 (permalink)
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Please go easy on me.....2

If I was to set cold lash of 20thou on a solid flat tappet cam, when the engine is at full operating temp would the hot lash be the same on all rockers?

If so , is the hot lash spec likely to be 22 or 25 or 30thou? Will the gap only open so far?

Or is it an unknown due to variables?

Does anybody understand my question?
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Old 11-03-2005, 15:36   #2 (permalink)
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Re: Please go easy on me.....2

depends on variables such as alloy or cast iron expansion....

I've set mine at 20thou cold ... then drove all day, got home and checked again whilst HOT, did not change... still a tight 20thou.. go figure
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Old 11-03-2005, 19:05   #3 (permalink)
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Re: Please go easy on me.....2

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Originally Posted by xrgt
depends on variables such as alloy or cast iron expansion....

I've set mine at 20thou cold ... then drove all day, got home and checked again whilst HOT, did not change... still a tight 20thou.. go figure
Alloy heads on a steel block WILL cause the clearance to open up between 4-6 thou for sure from cold to hot.
Steel heads i'm not sure how much, but usually expand at a similar rate from valve to valve from experiance.
I set my AFD heads to 20 thou cold and they end up at 25 thou hot.
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Old 11-03-2005, 20:19   #4 (permalink)
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Re: Please go easy on me.....2

Good work !

Thanks.
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Old 11-04-2005, 00:29   #5 (permalink)
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Re: Please go easy on me.....2

Ummm, the gap gets SMALLER doesn't it? WHich is why a lot of engines have a bigger gap for the exhaust then the inlet, as the exhaust valve runs hotter, which causes it to expand more, and hence you get a smaller gap at operating temp.
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Old 11-04-2005, 00:52   #6 (permalink)
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Re: Please go easy on me.....2

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Originally Posted by RPO-083
Ummm, the gap gets SMALLER doesn't it? WHich is why a lot of engines have a bigger gap for the exhaust then the inlet, as the exhaust valve runs hotter, which causes it to expand more, and hence you get a smaller gap at operating temp.
Yes, that is one of the reasons you adjust them at operating temp, ex valves expand more than inlet valves.
Adjusting them cold is not the correct way, the advertised clearances are hot clearances because the engine operates correctly when its hot, not cold. For best results adjust hot.
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Old 11-04-2005, 01:10   #7 (permalink)
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Re: Please go easy on me.....2

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Yes, that is one of the reasons you adjust them at operating temp, ex valves expand more than inlet valves.
Adjusting them cold is not the correct way, the advertised clearances are hot clearances because the engine operates correctly when its hot, not cold. For best results adjust hot.
That's good. Otherwise every engine manufacturer has got it wrong. I wasn't sure whether it was the worldwide manufacturers or a couple of FF guys who were mistaken.

One a side note, "hot sets" of the valves is pretty well old school in the bigger stuff. Now, any stabilized "cold" temp is preferred, as it is more consistent. But, I suppose on a car it doesn't take that long from start to finish when doing a set, and the metal temp (and therefore expansion) shouldn't change that much. But, then again, maybe the manufacturers got the procedure wrong as well....
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Old 11-04-2005, 01:18   #8 (permalink)
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Re: Please go easy on me.....2

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Originally Posted by RPO-083
That's good. Otherwise every engine manufacturer has got it wrong. I wasn't sure whether it was the worldwide manufacturers or a couple of FF guys who were mistaken.

One a side note, "hot sets" of the valves is pretty well old school in the bigger stuff. Now, any stabilized "cold" temp is preferred, as it is more consistent. But, I suppose on a car it doesn't take that long from start to finish when doing a set, and the metal temp (and therefore expansion) shouldn't change that much. But, then again, maybe the manufacturers got the procedure wrong as well....
LOL, people adjust cold because they don't want to deal with the hassle and inconvenience of a hot engine, if near enough is good enough then no problems.
Yes in newer stuff if you can measure or calculate the expansion rate of the various metals or alloys involved then you can work out a theoretical cold setting that should work out fine!
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Old 11-04-2005, 01:44   #9 (permalink)
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Re: Please go easy on me.....2

Quote:
Originally Posted by RPO-083
Ummm, the gap gets SMALLER doesn't it?
Yeah, the gap gets smaller if you use steel heads, but only by a couple of thou. If you use alloy heads, the gap gets "bigger" and like i stated is by approx 6 thou generally speaking. I'm sure people will dissagree, but they probably havn't used alloy heads i spose.
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Old 11-04-2005, 02:14   #10 (permalink)
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Re: Please go easy on me.....2

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Originally Posted by xdclevo
Yeah, the gap gets smaller if you use steel heads, but only by a couple of thou. If you use alloy heads, the gap gets "bigger" and like i stated is by approx 6 thou generally speaking. I'm sure people will dissagree, but they probably havn't used alloy heads i spose.
I see your point. I can't say 100 % that I have had to adjust solids on an alloy head, so therefore can't comment. Iron heads depends on the size of the valve, as to how much they expand. One engine I used to do was .014in and .027ex (cold), but I'm off-topic as it was far from a Clevo....
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