This is a question I've hesitated to pose because I thought the answer should be obvious - but so far it's "plumb evaded" me. I've got a 365 hp 1965 with a Holley 4150 with a metered orifice. I don't have a PCV on the hose between the MO and oil fill tube. I have a chrome oil fill cap (with cork gasket) that fits rather loosely on the tube. I've assumed that with the engine running, a slight vacuum would keep the cap tight - that's not the case. I've got a rubber cap that fits air tight, but the engine doesn't seem to run as well with it on. So I figured the somewhat loose chrome cap served a function by not being "air tight". I've jury rigged it by wrapping a couple of times around the oil fill tube neck with electric tape to give the chrome cap a tighter fit, and it works - but I know it ain't right. What am I missing here? Should there be a collar around the oil tube neck or do I just need a new oil fill tube (it has some chrome loss, but appears in good shape - not deformed). Appreciate any insight.
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David Hobby (46447) -
Re: C2 '65 365hp Loose Oil Fill Cap
David,
Does the cap attach to the outside of the fill tube or the inside?
There is a difference between different year tubes and caps. Non matching will not work together.
You mention a slight vacuum, how much vacuum.
Verle -
Re: C2 '65 365hp Loose Oil Fill Cap
The chrome cap fits over the oil fill tube. The cap's lip is slightly turned-in to "grab" the tube neck, which is turned-in to form a slight expansion at the neck for the cap to "grab". There doesn't appear to be a vacuum at the oil fill tube, the cap bounced off while I was driving, landing on the block and a small amount of oil was deposited on the air cleaner cover, so I figured it was an issue of the cap not fitting properly.David Hobby (46447)Comment
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Re: C2 '65 365hp Loose Oil Fill Cap
You may need to adjust the tabs on the bottom of the cap to tighten the fit, the system is designed for the cap to be tight. Does it have the gasket inside? worn or missing gasket could also be causing your problem.Bill Clupper #618Comment
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Re: C2 '65 365hp Loose Oil Fill Cap
A new cork gasket on the cap should snug it up. They compress and harden with age. Make sure the PCV restictor, which is the fitting on the carb is not clogged, and check the PCV component configuration with the AIM or shop manual to be sure it is correct. The PCV configuration on your engine does not have a PCV valve.
DukeComment
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Double Cork Gaskets did it for me ...
I was considering squeezing the tabs together in a vise, but adding another gasket underneath the original corrected the problem.Comment
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Re: Double Cork Gaskets did it for me ...
I'll give the new cork gasket a try and maybe double it up with the old one. Just a little paranoid about losing it. Thanks guysDavid Hobby (46447)Comment
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Re: C2 '65 365hp Loose Oil Fill Cap
The special fitting on the driver's side of the carb for the hose from the oil fill tube has an .090" orifice in it that meters the flow of crankcase vapors (forerunner to the PCV valve that started in '66). Cleaning that orifice with a fine wire was part of the normal tune-up routine, but most folks don't know that and most of them have been clogged for years.Comment
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Re: C2 '65 365hp Loose Oil Fill Cap
John - just to clear up any historical confusion, the '61 to '63 PCV systems used valves. Perhaps Chevrolet was looking for cost reduction by designing the "valveless system" used in '64-'65, but the fact that they went back to valves in later years is, perhaps, an indication that the "valveless system" was less than satisfactory.
Personally, I don't like it. That small orifice can easily get plugged and, as you said, is overlooked by most owners, so your advice to check the metering orifice should be followed by all owners of these "valveless systems".
If it's badly clogged it should be soaked in carb cleaner, then mechanically cleaned. If it's open a few passes with a pipe cleaner wetted with mineral spirits or paint thinner should clean make it squeakly clean, and this should be done at every "tuneup". Cleaning out the supply hose from the oil fill pipe is also a good idea.
DukeComment
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Re: C2 '65 365hp Loose Oil Fill Cap
John, My orifice is clear. But should the the oil fill cap on my system be "air tight" or loose enough for air to pass around the gasket? It just seems it wasn't designed to be "air-tight". I have another rubber oil fill cap that fits very tight and seemed to have a slight negative affect on the way my engine ran, although I couldn't swear to it - I didn't have any gauges to hook up. Just curious.David Hobby (46447)Comment
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Cap should be air tight...
What's the condition of the gasket?Comment
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Re: Cap should be air tight...
It's intact and,on initial appearance, looks fine, but does show an indentation where is has been compressed and probably due for a new one.David Hobby (46447)Comment
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Re: Cap should be air tight...
If the gasket doesn't have an impression then something is wrong - tabs on cap or filler tube or the gasket is too thin. Maybe a second gasket will create a seal. The last eighth turn of the cap should be stiff as the gasket compresses.
IIRC the gasket is fairly thick- say 1/8", and one of the proper thickness should definitely be depressed where it mates to the top of the fill tube.
DukeComment
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Re: C2 '65 365hp Loose Oil Fill Cap
David----
The oil filler cap on all Chevrolet engines with positive crankcase ventilation is designed to be "air tight" (within the normal pressure range of the crankcase).In Appreciation of John HinckleyComment
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Re: C2 '65 365hp Loose Oil Fill Cap
David, Long Island sells the new gasket you need. But it's very thick and typically I have to put it in a vise between two little boards and smash it a tad just so I can get the oil cap on. If your case you should be able to use it as is. JohnComment
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