BJ8 Dowel Bolts

[WHT]

Hi Bob,

Split lock washers are in my opinion horrible and should not be used. Their design is based on the premise that their split ends dig into the parent material on both sides of the washer to prevent the bolt/nut from turning. So, they damage the parts.

But, even worse, studies by NASA show they can actually cause the bolt to loose tension faster than using just a nut by itself. I would rather use two, hardened and ground flat washers with a reliable locking nut (and usually made-up with a locking gel).

"Helical spring lock washers have been in use for well over 100 years. They are still used on many applications in the belief that they will will "lock" the nut/bolt to the joint and prevent loosening. The body of evidence, based upon both experience and experimental results, is that they do not prevent loosening and can be shown to actually speed up the rate of loosening in many cases. Junker originally showed in his work published in 1969 that these washers are ineffective in preventing loosening. Joints containing these washers have come loose resulting in structural failure leading to both material and human loss."

Regards, Bill

 

[Bob_Spidell]

Look at the gouges in the shock on the left. When they dig in, it releases tension on the bolts. The clamp load of a 3/8" fine grade 8 bolt is 7,875 (> US Bolts - Tensile Strength and Proof Loads <). Let's say, for simplicity, the total area under the bolt head and split washer is 1/2"sq , and the total area under a grade 8 flat washer is 1" sq.; the clamping force is spread over a larger area (assuming no deformation of the flat washer--there's likely a very small amount). Given the crappy metal the shock bodies are made from--Al, Zn, 'pot metal?--I suspect it's not unheard of for an 'ear' to break off if the bolt loosens or breaks.

Years ago, I read a book by noted chassis builder Carroll Smith. In the book, he absolutely loathes lock washers of all types, and prefers threadlocker:

Nuts, Bolts, Fasteners and Plumbing Handbook: Carroll Smith: 9780578146041: Amazon.com: Books

Nuts, Bolts, Fasteners and Plumbing Handbook [Carroll Smith] on Amazon.com. *FREE* shipping on qualifying offers. Nuts, Bolts, Fasteners and Plumbing Handbook

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Over the years, I've found his information to be correct, with one exception for Healeys: The rear shock bolts wouldn't hold with just a grade 8 flat washer under the head with the nut secured with threadlocker (they don't hold with split washers, either). I suspect this is because the bolts are installed in shear. My most recent attempt is with Nord-Lock washers, recommended by a fellow forum user. I only have a few miles with them installed but have great faith. If you've ever had a rear shock bolt loosen, you'll know it makes an annoying 'knock' when you go over bumps. Leave it that way and you'll round out the holes in the shocks and possibly in the mounts, and you'll have a hard time getting them secured again.

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[Bob_Spidell]

Bill, Looks like we're in violent agreement except I won't use anything but grade 8 flat washers (except in inconsequential applications). I bet I'm not the only owner who has removed a flat washer from under a generator adjusting bolt that has been bent into a scoop. As a rule, though, I don't use a flat washer under nuts unless the hole is oversized.

 

[WHT]

Hi Bob,

I think we both agree on using better bolts and fasteners in the drive train where possible.

As you say, the average flat washer from the hardware store is too soft and often poorly made. Most (real) Grade 8 washer are good, as are hardened and ground washers.

I have all of Carroll Smith's books and started collecting them after "Tune to Win" and "Prepare to Win" were written in the 70's; and gave my son a copy of "Nuts, Bolts, Fasteners & Plumbing Handbook" when he was 12 years old (he did eventually read it ). Lots of great information on building cars that are safe, work well and use sound engineering practices.

I began to question split lock washers when I was a kid and started helping my Dad work on old cars (he restored Model A Fords and had a 1953 Studebaker that he liked and kept running). I found lots of old split washers that were either broken or smashed flat, with no spring left. Then, in the late 60s when I was in High School, NASA began publishing articles on bolt technology and aerospace fasteners. You wont find split lock washers used in their structures.

ARP also publishes good bolt technology articles. They had a good discussion several years ago about not lubricating the underside of washers (not the head or nut contact area which should be lubricated in many applications and they provide a good bolt lubricant). When the underside of the washer is lubricated, they found the washer could spin and act like a bearing. This increased the effective torque applied to the fastener and they were seeing more stripped thread complaints.

Nord-Lock are great IMO. I had a Corvette that had several fasteners that would not stay torqued. Like you, someone recommended Nord-Locks and everything stayed torqued during the 10 years I owned the car. They are expensive, but are well worth the cost.

We try to keep my wife's BJ8 original in areas where it makes sense, but do not use the original bolts, washers and nuts in critical areas like the drive train and transmission if better parts exist today. Although, any bolt/washer/nut replaced in her car keeps the original fine threading used by Austin-Healey.

Regards, Bill

 

[Bob_Spidell]

Ha! My dad had two As when I was growing up, a '29 roadster and a '31 coupe. I drove the '31 through JC; to this day I don't rely on brakes any more than I have to (one of the reasons I like manual gearboxes). He wanted to buy a '57 'Vette and a Stude Avanti, but never found ones he wanted.

The other day I needed new bolts for my shocks, but none of the local hardware box sellers had the exact size I wanted in grade 8. To my delight, I found a little store downtown, run by an older Asian couple, that have shelf after shelf of bolts, all in cardboard boxes marked with Sharpies. He said he had them, I said I'd come have a look and when I got there he had them in a plastic bag on the counter. Don't think he has any dowel bolts, though

 

[AUSMHLY]

Bill wrote: the holes for the "normal" bolts are larger in both the bellhousing and back plate, around 0.400-inches in diameter. The holes for the Dowel Bolts are smaller and about 0.372 to 0.375-inches in diameter and have a tight fit.
And, as you also know, after 50+years, the holes in the bellhousing and back plate can be worn and not always round.

I received the 2 dowel bolts. There is a lot of play when inserted.

I'll assume because the prior "normal" bolts have a larger diameter they made the Bellhousing holes larger.

Question: Should I use normal bolts with a shoulder length the same as the dowel bolts in all the mounting holes now, except for the bolt that screws into the rear plate?

Those should provide a tighter fit and hopefully line everything up better.
I'll get bolts long enough to put a flat washer on both ends of the bolts and use nylon nuts.

 

[Bob_Spidell]

Since you've had a odd collection of problems with your gearbox IIRC, I can't help but wonder if engine/bell housing misalignment is at least partially responsible?

 

[AUSMHLY]

Hello Bob, thanks for taking this ride with me. Let's say that's part of the issue. What would you do?

I have replaced the following with new; pilot bush,1st motion shaft bearing, main shaft bearing,1st motion shaft caged bearing.

 

[AUSMHLY]

Hi AUSMHLY,

My comments are for a center shift engine and gearbox.

It all depends on how you install the normal bellhousing bolts and the Dowel Bolts (head faces forward or to the rear). This is decided for you in 2 cases since the upper right bolt threads into the block and the lower right Dowel Bolt can only have the head facing to the rear.

The Dowel Bolts have the same shoulder diameter as most Grade 8, 3/8"-24 bolts (0.372-inches). However, the threaded portion of both bolts is only about 0.363-inches in diameter. The real difference then is the shoulder length of the two bolts. Dowel bolts have a shoulder length of 0.757-inches so the shoulder supports both the rear engine back plate and the bellhousing. The other "normal" bolts as sold by Moss have a shorter shoulder length of about 0.312-inches and only support either the back plate or the bellhousing depending on the direction they face.

I personally buy Grade 8 bolts with the correct longer shoulder length to support both and use them in all of the holes when possible; and only install them after installing the two Dowel Bolts and the threaded block bolt. So, I purchase longer bolts and shorten them. I use a shoulder washer and a lock washer to make sure the nuts can be torqued correctly.

If there is a fit problem (a smaller diameter is needed for one of the "normal" bolts to fit into the back plate), I install normal bolts and machine the shoulder diameter to fit.

As you know, the holes for the "normal" bolts are larger in both the bellhousing and back plate, around 0.400-inches in diameter. The holes for the Dowel Bolts are smaller and about 0.372 to 0.375-inches in diameter and have a tight fit. There is no magic here.

And, as you also know, after 50+years, the holes in the bellhousing and back plate can be worn and not always round. I have am installing a Denis Welch back plate to help ensure the best centralization.

You need to measure everything and decide the best way to install the various bolts to centralize the gearbox on the back plate.

Regards, Bill

Hey Bill, I spent some time measuring everything. I'm not sure dowel bolts are any help and they're expensive, $60 for two.
I found regular bolts, grade 5, provide a tighter fit and isn't that what we want to line everything up? Most likely because the holes are larger from prior owners using them. I can get bolts, grade 5, with a shank length the same as the dowel bolts.

Here are some photos. I've stacked enough washers on the bolt to compensate for both the bell housing and the back plate. If you add in two more shoulder washers for the bolt head and nut/split washer or nylok/nylon nut the dowel bolts aren't long enough. 1st photo dowel bolt with washers thickness of the bell housing only, no shoulder washer.

I don't have an grade 8 bolts to try. Do these grade 5 bolts have a larger shank diameter then grade 8?
I seem to have play with all the grade 5 bolts, but I was using the short ones. Maybe having the shank in the bell housing vs treads will help with tighten up the tolerance?

 

[Bob_Spidell]

Hello Bob, thanks for taking this ride with me. Let's say that's part of the issue. What would you do?

I have replaced the following with new; pilot bush,1st motion shaft bearing, main shaft bearing,1st motion shaft caged bearing.

If your bell housing bolt holes have been hogged-out I think about all you can reasonably do--short of finding another bell housing (not likely)--is to somehow sleeve the holes? Otherwise, you have to get everything aligned best you can and hope for the best. I don't know if misalignment is the cause of your problems, but nothing else is jumping out.

Here's a refurb'd bell housing for a BN2, I've seen others on eBay. I got a used oil pan and a gearbox cover on eBay.

 

[AUSMHLY]

I'll try bolts with a longer shank and see if it makes any difference when installing,

 

[WHT]

Hi AUSMHLY,

Sorry to be late responding, we have been away from town for a week.

Not sure about the Grade 5 grip diameter, but it sounds like an improvement. And, you really want the grip to extend into both the backplate and bellhousing as long as there is sufficient thread to allow for stretch when the bolts are torqued, as you said. Sounds like you found a good solution.

I am working on replacing the rear engine backplate to restore the bellhousing holes to factory specifications. It is surprising that even the steel backplate holes can be slightly out-of-round after 50 plus years!

Even worse, the bolts retaining the backplate had lost tension due to spring lock washers as was discussed earlier. The original lock washers were smashed flat and the plate was only held in position (quite aggressively I might add) by gasket cement and the two dowel pins. Every single bolt had lost tension! Please see the included picture.

I have ordered drilled head AN bolts with the correct grip and UHL specifications, and will use ground washers, Loctite and safety wiring to install the new plate.

Regards, Bill

 

[AUSMHLY]

My understanding, the reason for using a washer is so it doesn't turn, digging into the material like the bolt head would when turning without it. Correct?
Or is using a washer that's a larger diameter then the bolt head to help spread the load?

If the washers is to avoid the bolt head from contacting the surface while spinning and causing damage, is it necessary if you don't let the head turn? The bolt head will be on the tranny side of the clutch housing and I'll have a wrench on it so it's not rotating. I'll be turning/tightening the nut on the other end.

I can't help overthinking if it's really that importance that all bolts have a shank that's as long as the combined thickness of the clutch housing and back plate thickness. It appears the bolts from British vendors, the shank is only as long as the Clutch Housing. Is that what the factory used? If so, why didn't the factory use bolts with shanks long enough for both the housing/back plate? Why are the two dowel bolts the only ones with a shank that long? I understand those bolts have a smaller diameter, a longer shank then the regular bolts. But if their purpose is to align the housing/back plate, why don't all bolts have the same shank length as the dowel bolts?

 

[red57]

I can't help overthinking if it's really that importance that all bolts have a shank that's as long as the combined thickness of the clutch housing and back plate thickness. It is not important for all bolts to be long shank.

It appears the bolts from British vendors, the shank is only as long as the Clutch Housing. Is that what the factory used? Yes, except for the two dowel bolts.

If so, why didn't the factory use bolts with shanks long enough for both the housing/back plate? They did - the dowel bolts.

Why are the two dowel bolts the only ones with a shank that long? Because two are enough to locate the relative positions.

I understand those bolts have a smaller diameter, a longer shank then the regular bolts. No, the bolts do not have a smaller or larger diameter, it is the holes for the dowel bolts that are smaller to provide a tighter fit on the bolts which helps align the parts - the difference is the length of the shank to reach across both parts. All the rest of the bolts are just clamping the parts together.

But if their purpose is to align the housing/back plate, why don't all bolts have the same shank length as the dowel bolts? The two dowel bolts do the job of alignment and the rest are doing a normal bolts job of clamping.

 

[WHT]

OK, red57,

Why does this bother you so much?

Using bolts with a longer shoulder in every hole does nothing to degrade the assembly; and it removes the need for "special" dowel bolts in specific locations. Simply, less chance of error with absolutely no down side. New, quality fasteners are cheap in comparison to the cost of installing and centralizing a transmission.

First, just because the factory did it a certain way when all of the parts were still new (in a car that was designed to last 5-years), does not mean it is the best method today for a restoration using parts that have seen 50 years of service.

Second, the Healey factory did not always use sound engineering. Centralizing the transmission with bolts used to also clamp the parts together is a very poor design. They should have used dowel pins to centralize the backplate and transmission, but that would have require more parts and cost them more money.

So, the backplate-transmission joint is compromised at the very beginning by the factory. The question is, what are the best compromises today given the constraints imposed on us by the factory (risk and reward); and the wear that has most likely has occurred. This does affect joint design. What will produce the best outcome statistically with the least risks or worries?

Do you really want parts of the clamped joint to be possibly supported by bolt threads due to wear in a structure where the bolts are intended to both clamp AND locate the parts? After 50 plus years are your two backplate dowel bolt holes still in perfect spec and still perfectly round? You know, the two holes that have born the brunt of the forces placed on the joint for 50 years? You think the transmission will be still centralized as well as it was when new? We are talking thousands of an inch.

Given uncertain dowel bolt hole wear and new dowel bolts machined to who knows what standard, what provides the best transmission support and centralization?

(i) If the clamped joint could be supported with the bolt shoulder by any of the bolts if needed.
(ii) Or, if longer shoulders are only used for two special dowel bolts, and some parts might be supported by bolt threads due to wear.

For some reason, this really bothers you. You should do what pleases you, and the rest of us can do the same. However, please let us know how option (i) is worse than option (ii) and why we all need to do exactly what the factory did? As mentioned, the cost difference is minimal.

Regards, Bill

 

[red57]

Bill,

If your last post was aimed at me, I would like to clarify that nowhere in this thread have I indicated in any way that I am "bothered" by dowel bolts or anything you have written - I have no dispute about the dowel bolts function and am not at all bothered by this thread. I was trained as an auto mechanic in the '60s, served a full apprenticeship as a machinist in the '70s, worked as a structural welder/fabricator in the '80s, raced and maintained my 100-6 in the '90s and early 2000s - I have a pretty sound understanding of how things go together. I truly thought I was helping by copying the OP's last questions (post #33) and pasting onto a reply page (I'm not too computer savvy so I forgot the +quote function and copied and pasted instead) and answered them one by one (the bolding was not yelling, I was only trying to separate my answers from his questions to make it easier to read) as to why there were only two and not all bolts as dowel bolts, etc. He also said the dowel bolt shoulders (shanks) were smaller diameter which is not true (which you thoroughly explained in your post #7 and I agree with). I am in complete agreement with your posts and do not understand what I have said to set you off - besides, I was not talking to you, I was trying to help a fellow forum member.

By all means anyone can use dowel bolts at all locations and I never said anything about degrading the assembly by the use of longer shanked bolts or that the assembly can't be improved upon but with the non-dowel holes being slightly larger the benefit would be diminished. If the holes are all significantly enlarged (worn), then using bushings to bring them back to a correct size might be a good solution.

I don't know why you think I am "bothered" but I resent the attack as totally unwarranted.

Dave