1955 front engine mount plate.

[Tom B.]

I was recently given a front engine mount cross plate by a friend that has had it laying around for 50 years. It was left over from a project 1955 (#351) that we had taken apart to begin the restoration process on in 1975. I can't remember if it was on the car or purchased separately. The only way it could have been on the car is if a small block and a 409 (425 horse, 4 speed) used the same water pump. I think it is a 56-60. it looks like the one on my 59 but I don't know exactly what the difference is. My ancient 1960 parts manual lists the 55 as a different part number (3711636) than the 56-60 (3754586), so there must be some difference, even if very minor. Can anyone tell me what the physical difference is between the two parts? Thanks.

[Gary C.]

post a photo

[Tom B.]

here it is.

[Gary C.]

Tom,

Looks similar to the photo in the 53-55 Judging Manual.

Also looks similar to this one on e-bay which seller says is a 1957 https://www.ebay.com/itm/177357204879

Gary
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[Tom B.]

Yes it does, Gary. I have thought for many years that the only difference between the 56-60 and the 61/62 was the cut out for the water pump with the pipe plug in the top. The black one in the photo is a NOS 61/62 I've had since the early 70s. However, the red one has a slightly different contour on the passenger side. It's hard to see but when I put the contour gage on it the difference is obvious. That's why I thought it might be a 55, not having one to compare it to. I'll check it tomorrow to be sure it isn't slightly bent.

[Gary C.]

Tom,

The 57 March P&A lists between water pump and engine part #3728616

That part number is also listed in 58 P&A

Gary
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[Tom B.]

That makes me wonder just how many variations there were. The back of my mind is telling me there was a Restorer article on this topic years ago. I should look it up in my spare time.

[Rod K.]

Not sure how many variations, but somewhere in the '57-58 time frame the contour just to the right of the right side water pump mount added the "notch" in the lower edge to allow access to the freeze plug in the block in that location. No notch for pipe plug in the top of the water pump at that time, believe it came in about 60(?). The red pic you posted matches my '57, do I'd guess '55-'58 maybe? Black one '60(?)-'62(?). Just speculatin' here.

[Gary C.]

Rod,

57's front motor mount were like exactly like Tom's red photo.

The black photo matches the photo of the UK MIRA report analysis on the '61 Corvette.

Maybe some of the 58-60 members will check their cars to see if their front motor mount has the lower edge removed.

ebay listing with the lower edge notch https://www.ebay.com/itm/205669976232?chn=ps&mkevt=1&mkcid=28&google_free_l isting_action=view_item&srsltid=AfmBOoo3zl3zPFolt5 uSMq_cVROBxBRzP5X4MMVzSv_4tNxDQSsZxOdxo8E

This vendor claims change was made early 1958 https://www.corvettepacifica.com/pro...Hm9VqrR5hGpg2G

Gary
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image.png

[Ian G.]

The 58-60 Judging guide (both 4th and 5th editions) claim the freeze plug notch was added sometime in the 59 model year (part of that being 1958 of course). I can't provide any evidence for my 59 as I bought my plate to match the guide and the previous water pump mount was a replacement also

[David B.]

PN 3711636 is exclusive to the '55 Corv. and possibly early '56 model. It was designed 1-4-54 and underwent 25 MINOR revisions in 1954. The contour change to the pass side was made 2-3-56, these would probably be service parts. The GM print indicates the "Mfr's identification must appear on this part"
PN 3728516 was used EXCLUSIVELY for the 56-57 Corv. It was designed 7-18-55. The print indicates it is "Identical with 3711636 except as shown". The only difference shown in the 56-57 version was the top mounting holes. 3728516 had a short live span as it was discontinued 8-1-58 being replaced by the 1958 version PN 3754586.

[Tom B.]

My 59 (#881) has the cut out for the freeze plug like the black one (3786779, 61/62), but no notch in the top like the red one. It must be 3754586. The red one has this manufacturer's mark on it. The bottom hole on the right-side water pump mount is 1/2" instead of 3/8" like the rest of the bolt holes.