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BJ8 Dowel Bolts

AUSMHLY

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The BJ8 Clutch Housing gets bolted to the engine with (2) Dowel Bolts.
I believe they help center or line up the transmission.

I've been having issues with getting into 2nd gear for years.
When I took it out, I didn't have dowel bolts.
Now I'm rebuilding the tranny, bolted it back to the engine with regular bolts. Took it for a test ride to find gears are getting chipped and it's noisy.
I'm now focusing on everything related to the tranny.

How important are the Dowel Bolts?
What problems will there be if not used?
I think a lot of people use regular bolts, being they didn't know about them or that they cost $30 each.
I seem to be throwing good money after bad, replacing a lot of stuff that I'm not sure are related.
 
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AUSMHLY

AUSMHLY

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DOWEL BOLT, clutch housing to rear plate
Part # 17
A0D2656A-F795-4BCD-A949-2AB7E068749D.jpeg

 

Bob_Spidell

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I work on the "If it wasn't essential--and maybe even if it was--the BMC (Ford, GM, etc.) beancounters would have eliminated it" principle. Some say they've been fine without them, but the bolts apparently guarantee the engine and bell housing/gearbox will be in the correct relative positions; maybe you can get lucky without them. Are you feeling lucky?
 
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red57

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The dowel bolts are to ensure the concentric alignment of the engine crankshaft and the transmission input shaft.

However, if the crankshaft main bearings have ever been align-bored/honed, the crankshaft will be sitting a few thousandths higher in the block than it was when it left the factory, so the "alignment" would be off - and align boring is fairly common (all of mine sure have).

The difference in alignment with a dowel bolt vs a normal bolt is only a few thousandths, so would it be any different than align boring?

Is the bell housing doweled to the transmission case? Could there be slight mis-alignment there too?

I have a Toyota conversion, but I've never worried about it and never had a problem.
 
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AUSMHLY

AUSMHLY

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The dowel bolts are to ensure the concentric alignment of the engine crankshaft and the transmission input shaft.

However, if the crankshaft main bearings have ever been align-bored/honed, the crankshaft will be sitting a few thousandths higher in the block than it was when it left the factory, so the "alignment" would be off - and align boring is fairly common (all of mine sure have).

The difference in alignment with a dowel bolt vs a normal bolt is only a few thousandths, so would it be any different than align boring?

Is the bell housing doweled to the transmission case? Could there be slight mis-alignment there too?

I have a Toyota conversion, but I've never worried about it and never had a problem.
Thanks red57,

I don't know if the bell housing is doweled to the transmission case. I didn't do that and I don't know if any previous caretakers did.

I had the engine rebuilt 200 miles ago. Now that I'm rebuilding the tranny, I noticed the 1st motion shaft end is worn. I checked the condition of the Spigot/Pilot Bush to find it was broken into four pieces. I bought a new one and slid it on the shaft to find there is some play. I inserted it in the engine, with the 1st motion shaft in hand, I slide it in. There is a little play, less then before replacement.

I also have some play with the 1st motion shaft when it's installed in the gear box. There's a new roller cage between the 1st import and the main shaft.

With that knowledge of some play, and I'm using regular bolts, not the 2 dowel bolts, will installing 2 dowel bolts make any difference?
 

WHT

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Thanks red57,

I don't know if the bell housing is doweled to the transmission case. I didn't do that and I don't know if any previous caretakers did.

I had the engine rebuilt 200 miles ago. Now that I'm rebuilding the tranny, I noticed the 1st motion shaft end is worn. I checked the condition of the Spigot/Pilot Bush to find it was broken into four pieces. I bought a new one and slid it on the shaft to find there is some play. I inserted it in the engine, with the 1st motion shaft in hand, I slide it in. There is a little play, less then before replacement.

I also have some play with the 1st motion shaft when it's installed in the gear box. There's a new roller cage between the 1st import and the main shaft.

With that knowledge of some play, and I'm using regular bolts, not the 2 dowel bolts, will installing 2 dowel bolts make any difference?
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
 

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WHT

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I think AUSMHLY has moved on, but I am including these pictures in case someone looking at the Bellhousing/Back Plate bolts and fitment in the future stumbles across this thread. It would have helped me to have found more detailed information on the bolts when replacing the transmission in our car and understanding how the Bellhousing is centralized by the bolts.

The clamping thickness of the Bellhousing and back plate is 0.989-inches (BJ8 - can not discuss other models); and IMO you would like most of this thickness to be carried by the bolt shoulder if possible for best centralization. Dowel Bolts are shown in red circles.

Regards, Bill
 

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WHT

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Yes and no. They certainly will work.

However, their length is only 1-29/64-inches. The clamping thickness is approximately 0.989-inches. That leaves only 0.464-inches for two washers and a nut. That is the reason I use longer bolts, with the needed shoulder length, and then shorten them to the length I think is best. Flat washers at both ends have been proven to provide more accurate installation torque or strain measurements since the washers do not turn and do not dig into the base material. The factory often looked for the easiest and least expensive fitment.

Most parts diagrams show only a lock washer (which I do not use) and a conventional nut. But, when torquing to 30 to 35 pounds-feet, and centralizing the bellhousing, you might want two bearing surfaces to protect the bellhousing and back plate (even the steel plate) and a proper lock nut installed with at least two threads past the nut. Or, not.

Regards, Bill
 

dezand

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I used two of these on my BT7 and they fit correctly. Maybe on the BT7 the thickness of the engine plate and bellhousing flange is different. I used a washer under the bolt head which interfaces with the aluminum bellhousing. The unthreaded shank was approximately .030 shy of coming out of the engine plate.
 

WHT

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Hi dezand,

You have to order washers with an outer diameter that works with the bellhousing (McMaster-Carr has anything you need). Standard washers will not fit as you say. I have three bellhousing and two of them have some bolt damage in the soft aluminum flange where washers were not used. More than the damage itself, bolt torque will relax as the bolt head or nut digs into and deforms the aluminum.

I found your last sentence very interesting. One of my bellhousings is from a BT7 and its flange is 0.040-inches thinner than my BJ8 bellhousings. I don't know how common this is between years or models, but there appears to be variations in flange thickness based on your observations and one of my bellhousings.

My comments are for later BJ8 center-shift bellhousings. If you check my posts, I once asked the forum if all center-shift bellhousings were the same. The variation in flange thickness I saw was the main reason for asking this question.

Discussing the installation is great and people should use whatever they think works best for them. I do what I have done on our gearbox installation because I hope to never see the inside of our bellhosing again. :smile:

Regards, Bill
 

WHT

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Hi,

Just wanted to add several pictures showing variations in flange thickness and flange damage from bolts without two flat washers. A properly sized washer could have more than doubled the bolt's contact area.

The first picture shows a bellhousing hole that is worn oversize and the aluminum damage from not using a flat washer on the other side.

The second picture shows two of my bellhousings; a BT7 and a BJ8. You can easily see the difference in flange thickness as discussed.

Regards, Bill
 

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AUSMHLY

AUSMHLY

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I think AUSMHLY has moved on, but I am including these pictures in case someone looking at the Bellhousing/Back Plate bolts and fitment in the future stumbles across this thread. It would have helped me to have found more detailed information on the bolts when replacing the transmission in our car and understanding how the Bellhousing is centralized by the bolts.

The clamping thickness of the Bellhousing and back plate is 0.989-inches (BJ8 - can not discuss other models); and IMO you would like most of this thickness to be carried by the bolt shoulder if possible for best centralization. Dowel Bolts are shown in red circles.

Regards, Bill
Hello Bill,
Thank you for replying to my post. I should have thanked you and all that are chiming in. I'm learning a lot with this transmission rebuild. I'm currently focusing on the gears. I'll now take some measurements of the existing bolts. I've ordered 2 Dowel bolts. As I get more hands on with working on my Healey, I'm learning to question everything. Are these the right parts or was it assembled correctly.

As you pointed out, having a flat washer on both sides of the bolt make sense.
 

WHT

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Hi AUSMHLY,

I had not seen you post for a while and thought you might be busy on your transmission.

I ordered the Dowell bolts also before realizing they really only differed in their shoulder lengths. Mine were $32 each from Moss because I wanted them quickly, before taking everything apart and measuring it. o_O

Like you said, you quickly realize there are lots of surprises hidden in a 55-year old car and you have to question and examine everything.

Regards, Bill
 

Bob_Spidell

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I'm in agreement with Bill on the bolts and washers, and I'll add grade 8 flatwashers should be used, well, always. They're only a little more than cheap, flimsy 'standard' flatwashers that squash and deform easily. Here is a photo of a couple of front dampers; the one on the right was a spare damper I'd sent for rebuild; you can clearly see where a lock washer--used by the factory, I presume--had dug itself into the soft metal of the damper and released tension. The top damper was one I removed from my BJ8, where it had been in service for tens of thousands of miles, and you can see the grade 8 flatwasher I used had flattened-out the the 'countersink' made by a split lock washer.

Bill doesn't say why he doesn't use split lock washers but, for this and similar applications I use grade 8 bolts and flatwashers, secured with blue threadlocker and torqued to 35lb-feet. In over 100K miles I've never had a front damper come loose.
 

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