Show us the Aeromotive pump install on the Skylark. Are you going to be controlling the pump with the MS, or with the Aeromotive controller?
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The Silver Buick's 1969 Firebird OHC six project.
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Sweet - did you get the thanksgiving discount?
I would clean up the sharp edges in the head combustion chambers before you bolt it all down.
I can't believe with all your plethora of skills and experience you're still using plastigauge - pony up for some mics, bore gauge, and dial indicator! Even the cheap stuff is way better than relying on plastigauge.There's always something new to learn.
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Yup, I got the thanksgiving discount. It's what forced my hand versus waiting until Feburary or March. I still have to sort out what I'm going to do with that much pump on my Skylark's engine. Will probably have to pony up for the Aeromotive PWM controller to down grade the flow. There will probably be some re-engineering of my Skylark's fuel system again.
I'm going to leave this head more or less alone. Next month when I am in CA I am dropping off a head that will get the good treatment with some chamber re-shaping.
Plastigage, meh. I have a good set of mics, two pretty nice dial calipers, two dial indicators but no bore gauges for either the cylinders or the rod/main journals. I'm more or less an engine assembler at this point and simply wanted an idea of clearances, basically a magnitude of order measurement, which was easily achieved. Besides, by the time I'm measuring out to the fourth decimal point even me measuring with a dial indicator the measurements are suspect IMO.Escaped on a technicality.
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You could have bought -.001 bearings for that motor and returned the clearances to almost stock specs.
Sealed Power part numbers: (From Summit)
Mains: (Z) 4124MA1
Rods: (Z) 2020CP1
Even though the rear main's oil groove and holes are not right for the OHC, they do work. For your "throw-together" motor they'd be fine. For your EFI motor, have the rear main bearings worked on to get them right.Last edited by OHC 6 Sprint; November 28, 2012, 02:58 PM.
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Originally posted by TheSilverBuick View PostI'm kind of curious as to the effect of the ~40*F temps on the measured clearances.
It's all cast iron and steel (except for a relatively thin layer of babbitt) which have roughly the same coefficient of expansion - about ~6 ppm/*F.
Your delta T is -110 [-40*-70*]. You have an average set of dimensions like 2.300 & 2.306 and 2.000 & 2.006 for each bearing pair.
2.300 shrinks to 2.298482
2.306 shrinks to 2.304478
The difference (diametral) is 0.005996" versus 0.006", a "change" in your .003" gap (per side) of only -0.000002"
I did ignore the babbitt thickness. This layer - primarily Tin - has a coefficient of expansion of about 13 ppm/*F, slightly more than twice that of the steel & Iron. The thickness of the babbitt is probably like .010", so its total change in thickness over the temperature change is a whopping -0.0000143" (smaller) per side. This effectively opens the "per side" gap from 0.003" to 0.003012".
Bearings, fits, clearances and your motor oil are all designed to work within a specific operating temperature range. The values in the service manual for room temperature measurements have already taken this into account.
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Originally posted by OHC 6 Sprint View PostLittle to none. For what you have to measure with: Less than none.
It's all cast iron and steel (except for a relatively thin layer of babbitt) which have roughly the same coefficient of expansion - about ~6 ppm/*F.
Your delta T is -110 [-40*-70*]. You have an average set of dimensions like 2.300 & 2.306 and 2.000 & 2.006 for each bearing pair.
2.300 shrinks to 2.298482
2.306 shrinks to 2.304478
The difference (diametral) is 0.005996" versus 0.006", a "change" in your .003" gap (per side) of only -0.000002"
I did ignore the babbitt thickness. This layer - primarily Tin - has a coefficient of expansion of about 13 ppm/*F, slightly more than twice that of the steel & Iron. The thickness of the babbitt is probably like .010", so its total change in thickness over the temperature change is a whopping -0.0000143" (smaller) per side. This effectively opens the "per side" gap from 0.003" to 0.003012".
Bearings, fits, clearances and your motor oil are all designed to work within a specific operating temperature range. The values in the service manual for room temperature measurements have already taken this into account.Escaped on a technicality.
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I'm actually a Plastigage fan - as a final check. You use the mics, etc, etc. but as a last chance the Plastigage costs almost nothing and takes just a few minutes. If you (or the machinist) made a measuring error (it can happen even to the best) you'll catch it before parts are ruined.
So no, you don't count on it but.......
Dan
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Last edited by TheSilverBuick; November 29, 2012, 09:42 AM.Escaped on a technicality.
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that's a lot of work!
Cute little 14 lb injectorsMy fabulous web page
"If it don't go, chrome it!" --Stroker McGurk
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