Trying to locate a 427/435 timing chain cover. I can't find a good picture to know what to look for. Any guidance in this area would be appriciated (like characteristics specific to this part) a j-peg photo would be nice as well. Corvette Central offers one with the designation "GM re-issue". Is this just like the original? Thanks in advance for any help on this matter.
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Re: 67 BB Timing chain cover?
George, I can send a pic of a '69 L78 camaro cover which I believe is the same. The only difference I believe is the '67 didn't have the two dowel pin holes. The GM re-issue won't look the same as a gennie. If you'd like a pic send me an e-mail. Ted -
Re: 67 BB Timing chain cover?
George------
There were several big block timing covers used over the big block years. The basic configuration of the covers was the same over the 65-72 period. However, there were small differences. One difference, of course, involved the different timing pointers that were spot-welded to the cover. Some engines used an 8" balancer and some used a 7", so the part number for the assembled covers were different for this reason. There were also other small differences.
For 1965, the L-78 cover was GM #3860068. For 66 through early 1968, the SHP big block cover was GM #3885058. I don't know exactly how these covers differ. However, both covers have NO holes for the dowel pins and they have a hole in the bottom center of the front seal radius with a weld nut. The latter feature was used for a bolt which retained the the oil pan to the cover. The bolt passed through a hole in the center of the oil pan front seal radius, through the timing cover hole and was threaded into the weld nut on the timing cover. This feature was used for 1965 and 1966. I think that it was deleted for all or part of 1967 and thereafter, although I believe that the hole and weld nut remained on the covers through mid 1968.
Beginning in mid-1968, the covers changed. Holes for the block dowel pins were added. The hole for the pan-to-timing cover bolt remained, but I believe that the weld nut was deleted. The L68+ covers later became the SERVICE covers for 65-E68, but if you needed/wanted the center bolt, then you had to insert the nut yourself. The L68+ SHP timing cover was GM #3935443.
In 1971 the SERVICE timing cover for big blocks changed to GM #3975941. I'm not sure if this cover was used in PRODUCTION, or not. I believe that this cover did not have a welded-on timing pointer, but I'm not sure of that. I don't know how it otherwise differed from the earlier covers or if the deletion of the welded on timing tab was the only difference. This cover was used for 1972 also.
For 1973, the SERVICE timing cover was changed to GM #330850. This cover does not have a welded-on timing tab and it may have been used for SERVICE-only. I believe that 73-74 Corvettes originally used a cover with a welded-on tab. If so, I believe that the PRODUCTION cover was identical to the GM #330850 except for the fact that it had a welded on tab. I don't have the PRODUCTION part number for this piece, but such a number is moot, anyway. The 330850 has a "quarter-size round bump" at the lower driver's side of the cam center projection. I don't think that earlier covers had this feature, but I'm not 100% sure. I'd be interested in the observations of folks with known-original 65-72 big block timing covers relative to this or other features.
The GM #330850 is the cover which remains available from GM to this day and is the cover which I feel confident is the one described as "GM re-issue". It's configuration is VERY similar to the 65-E68 covers except for the dowel pin holes, the lack of a weld nut on the center of the timing cover-to-oil pan sealing surface, and the driver's side "bump" (IF I'm correct about the fact that this feature was not present on the earlier covers).
By the way, the 65-E68 Mark IV blocks without dowel pins represents an inferior configuration to later blocks with dowel pins. You don't think that GM added the dowel pins because the configuration without dowel pins worked just as well, do you? Why did they do it? Here's why:
Install a timing cover on a non-dowel pin block and leave the attaching cap screws loose. You will note that it is possible to move the timing cover a bit within the limits established by the size of the holes in the cover and the OD size of the cap screws. It's a small amount, but it's enough to prevent perfect alignment and the best seal between the crank snout and the cover seal. That slight mis-alignment can cause front cover oil seal leaks. Small leaks, of course, but leaks. It can also result in a slightly imperfect seal between the cover and the oil pan. Once again, another possible source of minor leaks.
So, for later 1968 the dowel pins were added to the block. This, of course, required a revised cover which included holes for the dowel pins. The dowel pins are designed to fit rather tightly in the holes in the cover. If you install a cover on the front of a later 68+ block and leave the cap screws loose, you will note that the cover can be moved VERY little----the dowel pins hold it in perfect alignment. By the way, leaving the cover screws loose in both of the above-referenced "tests" is just to illustrate the effect of the dowel pins. I am NOT saying that the purpose of the dowel pins is to be a "abck-up" if the screws loosen. That has nothing to do with the purpose of the dowel pins, at all.
Alas, even if one wanted to add the dowel pins to a non-originally equipped block, it would not be possible for all practical purposes. Having a machine shop precisely locate the location for drilling the dowel pin holes, which is ABSOLUTELY ESSENTIAL if the dowel pins are going to serve their purpose, would be extremely problematic, at best.In Appreciation of John HinckleyComment
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Re: 67 BB Timing chain cover?
Functionally I believe they'll work, but I believe there is a slight difference in physical appearance. The early timing covers had a full circle indentation approximately where the cam timing gear would sit verses on the later versions had approx. a 3/4 circle indentation. They left the part raised by the timing tab. I believe the reissue has the 3/4 circle indentation. With the short waterpump it will be less noticeable. Another thing is the timing tab. The early ones had the straight edge on the tab verses I believe the re-issue will have a notched edge.
This picture has the full circle.
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Re: 67 BB Timing chain cover?
Verses the partial circle
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Re: 67 BB Timing chain cover?
Ted------
Yes, the "missing segment" of the circle is also the part that I was referring to with the "quarter size" depression near the center "cam circle". I don't really understand why that was added.
The unpainted cover is identical to the current SERVICE cover except for the welded-on timing tab.
A few questions for you:
1) Do either of these covers have the weld nut for the "center bolt" and do they both have the hole for the "center bolt"?
2) Do you know what application/year that both of these covers were originally installed on? I'm especially interested in the unpainted cover. It pretty much has to be the L68 to 70 GM #3935443, the 71-72 GM #3975941 (or, PRODUCTION-equivalent with welded-on timing tab), or the PRODUCTION-equivalent of the 73-74 GM #330850.
The painted cover is almost certainly the 1965 GM #3860068 or the 66 to E68 GM #3885058.In Appreciation of John HinckleyComment
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Re: 67 BB Timing chain cover?
joe: the painted cover is typical 66 and 67 production big block. the 65 396 differs , i believe, in that the timing tab isn't cut in a circular fashon at 4 oclock when viewed from above, but rather is a true rectangle. mike.Comment
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Re: 67 BB Timing chain cover?
Joe, These aren't my covers, they're just pics off of ebay. I'm not set up with a place to post pics from yet. With that said, the unpainted one I would say is off of a 73 or so 454. It has the notched tab and has a hole in it. The hole I was told was for some type of timing probe the GM dealers used. I know the later ones had a tube in the hole. I would venture it's probably the GM #330850. There seems to be alot of them around.
The listing on the painted one stated it was off of a 65 - 66 396 w/7" balancer. I have a couple for '69 L78 396s with 8" balancer and they look like the painted one except they have the dowel pin holes, the timing tab is moved out, and like Mike says, the timing tab is flat vs. curved. Both have the hole but neither of them have the weld nut in the center of the bottom for the oil pan. Both have '69 date codes on them so I believe they're production units vs over the counter. I've seen some earlier HP covers without the dowel holes and they look identical to the L78s I have. I didn't check for the nut though. Hope this helps, TedComment
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Re: 67 BB Timing chain cover?
Joe,
Not 100% sure on this but I think the difference between 65 and 66 was the timing tab. I believe 66 was the first year for the new longer tab with "R" and several more degree marks on the bottom or retard end of the tab, a result of the new Calif emission timing settings of "after" TDC. I'll go look at my 425 HP car. Need someone to look at an orig 65 396 car.
MichaelComment
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Re: 67 BB Timing chain cover?
I think I have the cover you're looking for. I thought I was going to need it but it turned out I didn't. Let me know if you'd like a picture of it, it's an original cover.Comment
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Re: 67 BB Timing chain cover?
Ted------
Yes, I think that I'm starting to fill in the "gaps" in my understanding of the "evolution" of the timing covers used from 1965 to 1974. I'd still like to get some information regarding the presence or absence of the weld-nut on known-original 67 covers and also the details of configuration of the covers used for 71 and 72. I'm goint to post a new topic with a request that folks with these cars and/or parts check theirs for me.In Appreciation of John HinckleyComment
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Re: 67 BB Timing chain cover?
joe: weld nut present of vin18172, a 67 435. am certain the timing chain cover was never removed prior to my rebuilding the L-71. mikeComment
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Re: 67 BB Timing chain cover?
The timing tabs are different for the 7" and 8" harmonic dampers. The 7" style is a true rectangle whereas the 8" style has one end cut off at a 45 degree angle. As previously noted, they are located different distances from the crank centerline. You can buy a 7" style cover from the appropriate year (dirt cheap on e-bay) and carefully grind off the spot welds. You can buy the 8" style timing tab from Paragon and reattach it to the cover with a spot welder that you can but from Harbor Freight Tools for just over $100. Look where the 7" tab is welded and if you reattach the 8" tab to the same spot the timing will line up. The 8" Paragon tab has a larger "foot" like the factory ones to properly space the tab to the 8" location.
Good luck,
MarkComment
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Re: 67 BB Timing chain cover?
Mike-----
Thanks. That's what I was virtually certain would be the case but your confirmation nails it down.In Appreciation of John HinckleyComment
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Re: 67 BB Timing chain cover?
i too have done what mark suggests(remove incorrect configured timing tab from a correctly configured timing chain cover, bought the nice repo timing tab from Paragon and spot welded it in place BUT, one must index the engine before spot welding the new tab in place, otherwise your TDC could be off as much as 20 degrees if you eyeball the location of the new timing tab. is so, timing the critter will be an exercise in frustration. If you doin't know how to index an engine(no big deal but my command of the english language would probably confuse the heck out of the students), suggest ya have the local machine shop index and spot weld it for you. mikeComment
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