Motor mount bolt orientation, big blocks

[Everett Ogilvie]

I apologize in advance for asking this question again (see the archives), but I recently tested some commonly accepted information and found it to be false.

Most sources indicate that the passenger side through-bolt on the motor mount for midyear big blocks goes from rear to front (head towards the rear). This is reportedly because the fuel pump prevents installing it front to rear. We have a post about this in the archives where plant assembly methods are described, supporting the rear-to-front bolt orientation, but I believe that information was based on the belief that the bolt would not insert from front to rear IF THE FUEL PUMP WAS IN PLACE. To test this, I recently removed this specific bolt on one of my cars just to see how tight it is, and there is no clearance issue whatsoever with the fuel pump in place. I removed the bolt out the front side and reinstalled it several times, just to confirm how easily it can be done. Based on this observation, isn't it possible that some (if not many) were installed this way at the plant? The AIM does not show an exception, so why wouldn't we see variation? What is the historical source upon which this claim is based - observation of original cars?. My own observations on a handful of highly original cars are that the bolts were installed front to rear on both sides and this includes a Bowtie car. Obviously, every restored car has the passenger side bolt installed rear to front because of the perception out there and our Judging Guides. I realize that I am questioning one of the foundations of our culture, but if physical evidence indicates a procedure can be done, why would the practice not follow? I am truly seeking to understand here, not incite a riot - asking questions, testing norms, and doing research is the key to our knowledge base continually growing.

[Mike McKown]

Re: Motor mount bolt orientation, big blocks

Everitt:

I spent a little time looking in the archives for your reference. I was unsucessful in finding anything but maybe I can offer a reason why the thru bolts on the right side would have all been front to rear. It's called efficiency! Time study guys know that if you are repetitive you are more efficient than if you alter your process from one job to the next. The line operators know this also. Either entity would tend to discourage deviation for their own reasons.

I think it is a given that the small block bolt will not clear the fuel pump. The big block, I don't know but will accept the fact it will go either way. First, the bolt head is I believe 5/8 and the nut is 11/16. You have one power tool and one holding tool. If this securing operation were done from a pit,(I don't know) the operator would secure one side and then turn and do the other side without swapping tools from one hand to the other. This could only be done if the bolts were reversed, one side to the other. If this operation were performed topside, the operator would have to change hands on his tools depending on which way the bolts were placed. If the operator that installed the bolt was the same one that secured it, he would do them all the same way. If the operator that installed the bolt put some in one way and some in another in a random fashion, I guarantee the two would be meeting in the parking lot after work.

Assembly operators usually like to fine tune their tools and as such, an air motor set up for the left hand will not be comfortable in the right hand. Same for holding tools. Also, you could have an issue of tooling clearance if you tried to go from one side of the mount to the other. Therefore, I find it highly unlikely that an operator would just arbitrarily change the process.

By the way. The Camaro and Novas of the late '60's that I have noticed are bolted in the same as described above.

This is not meant to offer PROOF of anything. Just to address your question of why there would not be deviations to the process. Of course, well all know that all processes have deviations. It's just a question of how much.

Mike

[Everett Ogilvie]

Re: Motor mount bolt orientation, big blocks

Thanks for the response Mike. You can find the original question in the most recent archives. I just reviewed it and here is a summary. When I originally asked the question, I wondered if fuel pumps were installed after the engine was set into the frame, and theorized that if that were true, then the through bolt could have gone in from the front. John H. has great knowledge of the plant, as he was there at the time, and he corrected me stating that the fuel pumps were installed on the engine dress line before the engine was dropped into the frame. This seemed to answer the question for me, until I recently observed that the bolt easily clears the pump on a big block, which prompted me to ask about possible variation on big blocks.

You make good points about efficiency, and I would be very interested to know some specifics (done from above or in a pit? one guy on each side or one guy does both sides? one guy pushes through the bolt and another guy secures it, or the same guy does both?, etc.) I am inclined to think that with humans involved, and the fact that the bolt on a big block will go either way, examples of both orientations came out of the plant. There are too many variables to make the claim that every big block came out with the same orientation. Take the case of two installers, one on each side of the car, and focus on the passenger side installer from two different shifts - what if the guy on first shift was right handed and the guy on second shift was left handed? Big block cars assembled by these two shifts would probably have different orientations as each guy would probably hold the securing tool in a different hand. This is just one possible way that variation could enter the system. If the bolt would go in either way I can almost guarantee someone found a way to install them either way. Statistically, it is inconceivable that there would not be some standard deviation in the process. It makes sense to state that the orientation for small blocks is always reversed from side to side because the situation dictates it - the passenger side bolt won't go in from the front. Extending that logic to big blocks is another matter and I believe it would be more accurate to say that big blocks might be observed with either configuration.

[Everett Ogilvie]

A Few Assembly Questions Answered

For those who may be interested - there are two very clear plant photographs in Noland's book (pp 28, pp 359) showing one guy on each side of the car as the engine is lowered into place (no pit, no guy doing one side and then rotating to do the other side, no guy installing the bolt with another guy tightening the nut, etc). These photographs lend credence to the possibility that the guy on the passenger side could have put the motor mount bolt through on a big block from either direction, and depending on the individual's ambidexterity, these bolts are likely to be found in either orientation. In addition, there appears to be a high likelihood of different bolt orientations coming from a right-hander vs. a left-hander.