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Re: Now here is an interesting item
"Super Chevy Technical Service Bulletin" Really? I'm impressed.
It does look like an interesting piece at a reasonable price, if one were interested in C1s.Terry -
Re: Now here is an interesting item
I am very inyterested in 56s, and a history buff on top of that, so it really got my attention.
I had not seen this service bulletin before. It might help explain why so many 56s no longer have the non-vented oil cap.
I'm tracking it on Ebay.Comment
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Re: Now here is an interesting item
I can almost guarantee the part numbers are no longer good, but I wouldn't be surprised that Joe Lucia could tell us all about them and when they went away. I have a collection of newer versions of this stuff. C3s mostly, as you might expect. There is a lot of interesting information in them, and a lot of useless information. This might be one of the former.TerryComment
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Re: Now here is an interesting item
One of the things I really like about the new 56/56 judging manual is the addition of a number of service bulletins that have been added to the manual. Lots of good info there.Comment
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Re: Now here is an interesting item
If a person has a copy of the most recent 56-57 judging manual, you'll notice there are never seen before pages covering such things, which were at one time RPOs, as the unique parts for the MINIMAL quantity of 56 SR1 cars. Thanks to a few people (John Neas, myself and others) who raised major complaints in the past few years, some of these things have now been included. UNFORTUNATELY, it took a while to convince some people that these were legitimate RPO parts and should have been accepted long ago by NCRS.Comment
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Re: Now here is an interesting item
remainder of page: breather holes 1552719 *nonpublished part - must be ordered on special order through your zone parts and accessory department (*applies to part #1552940)Comment
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Re: Now here is an interesting item
John------
I'm glad you could read the numbers because I sure couldn't.
GM #1552719 was once available in SERVICE. This was an AC Spark Plug Division part number and was an oil cap applicable to 56-57 Corvettes, 56-57 passenger cars with 2X4, 1958-61 passenger cars with high lift cam (except 348) and 1958-62 Corvettes with SHP. It was discontinued without supercession in September, 1972.
There is one strange thing about this piece. It apparently existed well prior to 1956 but it was discontinued without supercession in January, 1957. Then, sometime in late 1957 or early 1958, it "came back".
I can't find any record of 1552940, though.In Appreciation of John HinckleyComment
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This may help older guys like me!!Comment
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Re: Now here is an interesting item
Better yet.
Russ
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Re: Now here is an interesting item
Smarty pants
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Re: Now here is an interesting item
when we showed up at daytona beach in 1957 with our 57 FI 150 chevy sedan for the NASCAR beach race chevy gave us the closed breather cap and told us to safety wire it in place. they also gave us analine for the gasoline to prevent detonation but just like smokeys FI race car we burnt a piston because of the fuel shut of feature when you backed off of the gas built into the 57 FI unitsComment
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Re: Now here is an interesting item
for the road draft tube to work properly there has to be a place for the air to go into the engine for the road draft tube to pull out the fumes. i guess the high RPM engines would push oil vapors out thru the vented cap and GM wanted to stop that.Comment
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Re: Now here is an interesting item
No matter how precise and well built an engine is, THERE WILL BE a certain amount of blowby (combustion pressure going down the cylinder walls past the piston rings). This blowby puts (depending on the wear condition of the engine) pressure in the crankcase. My whole point here is that it IS NOT necessary for a fresh air source entry point for the crankcase. All that is NECESSARY is an EXIT point for the pressure buildup resulting from blowby. If no exit point existed for this pressure in an engine-------------THE SEALS AT EACH END OF THE CRANKSHAFT WOULD BLOW OUT------------and that has happened to a few unfortunate folks who did not understand this!
In fact, there ARE some engines that DO NOT provide an inlet source for crankcase air, only an exit-----------by way of a PCV valve!
Engines prior to 1963 (62 in Calif), a road draft tube system was used to allow vapors/pressure to escape. As the vehicle moved along the roadway, the air passing over the end of the road draft tube (notice road draft tubes are always angled toward the rear of the vehicle) created a vacuum and sucked out the vapors/pressure. Then in 63 (62 for Calif) a positive crankcase ventilation (PCV) system was installed on all engines. And some auto manufacturers sold retrofit PCV kits to install on older vehicles. The early PCV systems had an inlet (usually a breather type oil fill cap) for fresh air and a PCV valve plumbed into the fuel intake (usually the base of the carb, or FI plenum). Shortly thereafter, the fresh air inlet was a hose between the air filter and the crankcase so that clean, filtered air, instead of unfiltered outside air, was introduced into the crankcase. But all of the crankcase vapors/pressure (now dirty air) were STILL sucked into the intake manifold by way of a PCV valve. On heavily worn engines, or engines that are subjected to severe duty (ie racing) conditions, that little ole PCV orifice just is not sufficient to allow excessive pressures to escape from the crankcase. So, guess where they go???
Anyone ever seen headers on a race car where there is a hose running from each valve cover to a check valve plumbed into the header collector? The header collector is sucking all that high pressure blowby out of the crankcase!
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