Decent Torque Wrench for Engine Assembly?

[Duke W.]

Re: Decent Torque Wrench for Engine Assembly?

He told me that when you torque a bolt and you reach the torque value you want, you need to hold the torque for short period of time because a bolt will continue to turn or creep until it actually settles at the necessary torque.
Steve

...never heard that one before. I'm in total agreement with post #13.

BTW, steel is not subject to signficant "creep" as long as loading is within elastic limits. Elastomers are subject to creep, which is why exhaust hangers stretch over time.

If steel had as much creep the Golden Gate Bridge would have noticeable sag after over 75 years. The same applies to suspension springs. Unless they are severely overloaded or severely corroded they should maintain their original characterisitics indefinitely.

Duke

[Tom B.]

Re: Decent Torque Wrench for Engine Assembly?

Speaking of Harbor Freight and torque wrenches- the last time I was there I saw a gadget that attaches to any ratchet handle and it becomes a digital torque wrench. It was relatively inexpensive and displays torque digitally. Any comments? Anyone have any experience with one?
Jeff

I looked at those too and almost bought one to see how it worked. If it ever stops snowing I might run down there before work tomorrow. I need a tire and tube for my utility wagon.

[Michael G.]

Re: Decent Torque Wrench for Engine Assembly?

Duke, the only metal commonly used in vehicles these days that creeps appreciably is magnesium. Under load, he magnesium tends to flow so as to eliminate the load. Those of you who owned real "mag" wheels back in the day will remember that you had to re-torque the lug nuts fairly often or you rapidly lost clamp-load and maybe a wheel or two....

[Steven B.]

Re: Decent Torque Wrench for Engine Assembly?

I guess that "creep" was not actually the best word for what I was trying to suggest. The fact is that a fastener will continue to turn even after you have reached the desired value as indicated by the torque wrench. The whole idea behind torquing a fastener is to promote the appropriate amount of stretch in the fastener, at least in the higher grade fasteners. That is why they make gauges to measure rod bolt stretch. With rod bolts, you may wind up with a variety of actual torque values in order to gain the amount of stretch desired (most people don't go to that length in engine building). Since you can't accurately measure the stretch of some bolts such as main bearing bolts, the next best thing is to try to come as close as possible with a torque value. Most major components will have a specific torque value indicated as opposed to a range. This is evidenced in the chassis service and shop repair manuals produced by Helm for Chevrolet in the 60's.
The person I referenced in an earlier post was a gentleman by the name of Everett Hatch who lived near Stayton, Oregon. He owned Hatch Engine Service. Everett was respected as an engine builder and put together engines that had a reputation of having a bullet-proof lower end. You never knew what you might see next when visiting his unpretentious facility. On one occasion they had a $100,000 Mercedes aluminum bare block that had been sent from Europe and were machining for DeAtley Motorsports (I could be mistaken on the cost, but I remember that I thought it astronomical at the time). DeAtely would park their semi at Everett's and work right at his facility. That was in the mid to late 70's. Everett had a private landing strip at his facility and very often people would fly there from most anywhere, like up from California to do things like test a new fuel injection system. Unfortunately, Everett was lost in a plane crash in the late 90's. He was flying an experimental plane and it was suspected that a medical condition may have led to the crash. I was truly disappointed to hear of his loss. He was a great resource and I learned a lot from him.
I know that the torque values listed in a previous post indicate a range. These suggest that it would be OK to torque the head bolts anywhere from 60 lbs. to 70. Sounds a little too general to me. One other value that I wondered about was the 3/8 24 carburetor nut at 45 ft. lbs. I would be concerned that at 45, the nut would be pretty hard on the carburetor unless you were using a flat washer. I would also be inclined to use an inch pound torque wrench for pan and valve cover bolts. The values are all listed in the service manuals. It's much more accurate and less likely to wind up stripping a bolt hole (been there, done that). Just my two cents worth.

Steve

[Michael G.]

Re: Decent Torque Wrench for Engine Assembly?

You obviously know a bit about tightening fasteners, Steve. When you "stretch" a fastener, it acts like an "extension spring" and compresses the components it's attaching, like compression "springs", until equilibrium is achieved. Torque is only a means of estimating how much how much you have stretched the bolt, and/or how much clamp-load is in the joint. In an assembly plant, the goal is to achieve one torque spec, which will give you a range of stretch and a range of clamp-load. The problem is, you CAN'T achieve ONE torque in production, you will get a range. Their WILL be error, which means you can have a single target torque, but, in reality, you need to allow a range of torques. Hence the allowable torque range.

In all candor, in a previous life, one of the things I did on a daily basis was develop tightening specifications for GM cars. I did it for many years and many, many thousands of vehicle attachments. In fact, every spec, for entire car lines. As such, I might just have a pretty good idea how we specified torque values. I could, and often did, lecture for hours on how and why to develop such specifications, but believe me, if I did, we'd both be bored to tears after a few minutes. So, let's just assume I'm correct.

Virtually all GM torque specifications were stated by GM as a range. Look in the AIM, that is the GM document, used to assemble GM vehicles, in GM plants. GM fastener engineers placed those numbers in the AIM; they are specified as a range, for the reasons I noted earlier. If you would like a more detailed explanation, just PM me and I'd be glad to help.

[Steven B.]

Re: Decent Torque Wrench for Engine Assembly?

Mike,

Thank you for your service to GM. I really don't profess to be an expert, just a student that tries to pay attention. I believe that the original post was concerning acquisition of a torque wrench for assembling an engine. Granted, the torque values in the AIM are in ranges. I appreciate the manual, and have one for '67'. The manual is for assembling vehicles and attaching some engine components. I think that we could agree that attaching bumper bolts is not quite as critical as torquing rod bolts and nuts. I appreciate the fact that a range is sufficient for most situations as it should be. Many fasteners could be adequately tightened with a socket and ratchet. However, I don't believe that there are any values for internal fasteners within the engine included in the AIM, at least that I have seen. It is an invaluable resource but for engine building I would be inclined to go to the overhaul manuals. I understand what you mentioned about target values. Chevrolet manufactured production engines. Tolerances were close and the designs IMO were some of, if not the best ever, particularly the small block. The engine service I mentioned in a previous post dealt with putting together engines that were most likely to see extreme service. Where GM was dealing with tolerances to within thousandths, they were dealing to within tens. They didn't usually align bore for example, they would align hone. It required less material removal off of the caps, and didn't have as much tendency to move the mainline closer to the cam as align boring does. I guess my point is that it doesn't cost a lot to be deliberate or careful. The carburetor nuts for example in the AIM are in an inch pound range not foot pounds. So in addition to a ft.lb. torque wrench, one should have an in.lb. torque wrench as well. I prefer the old school beam type torque wrenches. The next best thing IMO would be a dial (best of both worlds but more expensive). The last choice (mine anyway) for engine assembly would be a click type torque wrench unless just close enough is satisfactory. Personally, I like to see and watch the torque value when I'm getting close. If you are torquing a head , your'e going to go around more than once and constantly setting a wrench is not what I care to do (call me lazy). If one is really into engines, you would want to be able to keep track of break away torques on dissassembly as well. That's probably getting out there for a once in a while engine assembly. I will continue to hold the torque value briefly after I reach it. It certainly will not hurt, and I have watched fasteners continue to find home after reaching the desired value.
As to boring me, that would not be an option. I'll pick anybody's brain if they'll let me. I am always interested in history, particularly how things come to be engineered. It seems that the older I get, the more I wished I knew.
A PM would be great.

Steve

[Michael G.]

Re: Decent Torque Wrench for Engine Assembly?

Without delving too deep into things, specially built engines are no different than anything else. It is impossible to specify a single digit torque and have anyone, anywhere, hit it perfectly with any known torque delivering device. That is why there are acceptable ranges for EVERY fastener, no matter how critical. There are much, much more sophisticated ways to tighten fasteners than torque and even the best of those have a range of acceptable values. Really

It doesn't really matter what torque wrench you utilize. If the wrench is reasonably calibrated, it'll be fine for tightening any Corvette fastener that has a torque spec. If you tighten close to the mean or target torque, nothing bad is going to happen. It is very difficult to make a big enough error to be outside the permissible range, let alone apply a low enough torque to allow failure, no matter what torque wrench you use. Some wrenches are better than others, but the differences won't take you outside the range of acceptable values.

[Joe L.]

Re: Decent Torque Wrench for Engine Assembly?

You obviously know a bit about tightening fasteners, Steve. When you "stretch" a fastener, it acts like an "extension spring" and compresses the components it's attaching, like compression "springs", until equilibrium is achieved. Torque is only a means of estimating how much how much you have stretched the bolt, and/or how much clamp-load is in the joint. In an assembly plant, the goal is to achieve one torque spec, which will give you a range of stretch and a range of clamp-load. The problem is, you CAN'T achieve ONE torque in production, you will get a range. Their WILL be error, which means you can have a single target torque, but, in reality, you need to allow a range of torques. Hence the allowable torque range.

In all candor, in a previous life, one of the things I did on a daily basis was develop tightening specifications for GM cars. I did it for many years and many, many thousands of vehicle attachments. In fact, every spec, for entire car lines. As such, I might just have a pretty good idea how we specified torque values. I could, and often did, lecture for hours on how and why to develop such specifications, but believe me, if I did, we'd both be bored to tears after a few minutes. So, let's just assume I'm correct.

Virtually all GM torque specifications were stated by GM as a range. Look in the AIM, that is the GM document, used to assemble GM vehicles, in GM plants. GM fastener engineers placed those numbers in the AIM; they are specified as a range, for the reasons I noted earlier. If you would like a more detailed explanation, just PM me and I'd be glad to help.

Mike------


Yes, the AIM's, including the engine AIM's, always specify a torque range for fasteners. However, the GM factory service manuals for older Corvettes usually do not. They specify only a definitive value. However, I have found that the value specified is usually right in the middle of the range shown in the AIM (for those fasteners shown in the AIM). In any event, folks should know that the torque does not have to be "dead-nuts-on" to any definitive values shown in the FSM.

At some point, GM started presenting torque ranges in the factory service manuals.

[Joe L.]

Re: Decent Torque Wrench for Engine Assembly?

All-------


My opinion:

"World's Best Torque Wrench" This wrench is accurate as well as fast and easy to set.



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"World's Worst Torque Wrench" Craftsman Digitorque. I bought this turkey quite a few years ago, although, as far as I know, it's still available. Trying to set this toque wrench with the tiny "windows" and with internal lubricant often obscuring the numerals, is a real treat----a treat that gets old REAL FAST. I've used this thing only a few times.


DSCN2937.jpg DSCN2938.jpg

[Edward B.]

Re: Decent Torque Wrench for Engine Assembly?

It doesn't really matter what torque wrench you utilize. If the wrench is reasonably calibrated, it'll be fine for tightening any Corvette fastener that has a torque spec. If you tighten close to the mean or target torque, nothing bad is going to happen. It is very difficult to make a big enough error to be outside the permissible range, let alone apply a low enough torque to allow failure, no matter what torque wrench you use. Some wrenches are better than others, but the differences won't take you outside the range of acceptable values.

Probably the best summary of the entire thread! Please do not overthink the entire concept. Torque ranges are well researched - aim for the middle and all will be OK. Just make sure you have wrenches that covers the applicable ranges and are of decent quality. One designed for ft. lbs. and one for in. lbs. would appear to be appropriate for our uses.