dowel bolts

[rjc157]

Need to take out the trans why are the dowel bolts different can you tell the difference I know I miss matched them does it really matter I know about the alignment

 

[steveg]

Need to take out the trans why are the dowel bolts different can you tell the difference I know I miss matched them does it really matter I know about the alignment

On my car, when viewed from the rear, the dowel bolts are at the 1 and 7 o-clock positions. I think these are the correct positions, but couldn't find anything in the manual about it. They have longer, beefier smooth-machined shanks compared to the other bolts, and are an accurate fit in the holes for locating the trans.

 

[TimK]

On my car, when viewed from the rear, the dowel bolts are at the 1 and 7 o-clock positions. I think these are the correct positions, but couldn't find anything in the manual about it. They have longer, beefier smooth-machined shanks compared to the other bolts, and are an accurate fit in the holes for locating the trans.

My info came from Healey Surgeons: dowel bolts are at 11:00 and 5:00 Upper left and lower right. Maybe it doesn't matter, but that's what I was told.

The dowel bolts are the grooved ones #3 and #4 from the left.

 

[Keoke]

My info came from Healey Surgeons: dowel bolts are at 11:00 and 5:00 Upper left and lower right. Maybe it doesn't matter, but that's what I was told.

That info is correct,and it does matter as these bolts have special shoulders on them [As shown in the Picture provided above ] wich fit in close tolerace holes in the bell housing to facilitate aligning the tranny / bell housing with the engine.

The remaining attachment bolts do not have these shoulders and fit into slightly over sized holes.-FWIW

 

[Healey Nut]

It dont matter , dowel bolts , BS Im saying . The tranny alignment is set by the output shaft going throught the clutch assembly and into the splines . No amount of dowel bolts and pegs etc will change that .

 

[TimK]

It dont matter , dowel bolts , BS Im saying . The tranny alignment is set by the output shaft going throught the clutch assembly and into the splines . No amount of dowel bolts and pegs etc will change that .

That seems odd, the splines are on the clutch disc; as soon as you engage the clutch the disc is free to move. I'll rely on the dowel bolts.

 

[Healey Nut]

OK for S##s and giggles try this . Install the tranny on the motor clutch etc all in place and see how much side to side up down movement there is ??

 

[steveg]

OK for S##s and giggles try this . Install the tranny on the motor clutch etc all in place and see how much side to side up down movement there is ??

Engineers don't get paid to drive up the cost by putting superfluous parts in cars. Therefore we can assume the dowel bolts are necessary.

The engine plate has 2 separate dowels locating it to the engine, rather than dowel bolts. The dowel bolts enable accurate location of the transmission to the back of the engine without putting excess sideways pressure on the pilot bearing and other bearings in the transmission. Ordinary bolts go in holes with "slop" in them for easy assembly and the dowel system is cost-effective compared to drilling all the bolt holes excessively accurately.

 

[Keoke]

Engineers don't get paid to drive up the cost by putting superfluous parts in cars. Therefore we can assume the dowel bolts are necessary.

-------Plus some of the earlier cars have permanent Dowell pins installed to effect this alignment.--

 

[Healey Nut]

The dowel bolts are just over enginnering . Pity they didnt put more engineering into the chassis and suspension on the Healey . Dont get me wrong I love my Healeys and always will . Im on my third restoration on Healeys right now and never used a dowel bolt on a transmission yet. No noises , no leaks no problems .
Lets face it its a Healey ..not a space shuttle , not a 10,000hp top fuel dragster or a 750mph jet powered land speed record breaker . Lining up the gearbox to the motor and bolting up with regular bolts and common sense you will be fine .

 

[Bob_Spidell]

Revisiting, as I'm installing an engine and gearbox and thought of this discussion.

I, too, wondered why the 'overengineering.' But, after a lot of thought it occurred to me that the purpose of the dowel bolts isn't just to make mating up a gearbox to an engine a frustrating task, or to spend money unnecessarily, but to solidify--can't think of a better word--the whole drivetrain. IOW, when the engine produces torque, it wants to twist against the gearbox, and without the dowel bolts, or similar mechanism, the block, rear engine plate and bellhousing would work (twist) against each other. I suspect that is why there are dowel pins in the rear engine plate/block--can't remember where they are--and dowel bolts between the engine plate and the bellhousing; without them the three parts could twist in relation to each other when torque is applied from engine to rear wheels. IOW, you have three flat surfaces--block, engine plate, and bellhousing/tranmission--that are being encouraged to slide against each other, and the dowel bolts are there to mitigate that movement. It may not make a huge difference, but the dowel bolts would prevent or minimize any fretting in the (relatively) oversized holes of the plate and gearbox. Since the front engine plate does not torque against another component, they are unnecessary there.

That's my theory, at least, and it makes sense to me; if someone knows the canonical truth please correct me. And, you'll say, 'Why don't the bellhousing and gearbox have dowel bolts or pins,' and my guess would be that that the relatively small surface of the area, relatively large number of bolts, and protuberances from the gearbox eliminate the need. Again, just a guess.

And, there's something to be said for doing things right, not just what you can get away with or, in this case, without.

 

[volts101]

Revisiting, as I'm installing an engine and gearbox and thought of this discussion.

I, too, wondered why the 'overengineering.' But, after a lot of thought it occurred to me that the purpose of the dowel bolts isn't just to make mating up a gearbox to an engine a frustrating task, or to spend money unnecessarily, but to solidify--can't think of a better word--the whole drivetrain. IOW, when the engine produces torque, it wants to twist against the gearbox, and without the dowel bolts, or similar mechanism, the block, rear engine plate and bellhousing would work (twist) against each other. I suspect that is why there are dowel pins in the rear engine plate/block--can't remember where they are--and dowel bolts between the engine plate and the bellhousing; without them the three parts could twist in relation to each other when torque is applied from engine to rear wheels. IOW, you have three flat surfaces--block, engine plate, and bellhousing/tranmission--that are being encouraged to slide against each other, and the dowel bolts are there to mitigate that movement. It may not make a huge difference, but the dowel bolts would prevent or minimize any fretting in the (relatively) oversized holes of the plate and gearbox. Since the front engine plate does not torque against another component, they are unnecessary there.

That's my theory, at least, and it makes sense to me; if someone knows the canonical truth please correct me. And, you'll say, 'Why don't the bellhousing and gearbox have dowel bolts or pins,' and my guess would be that that the relatively small surface of the area, relatively large number of bolts, and protuberances from the gearbox eliminate the need. Again, just a guess.

And, there's something to be said for doing things right, not just what you can get away with or, in this case, without.

Bob,
Only yesterday I did this job. I am of the opinion that the dowel bolts are to locate the bell housing relative to the engine and so they should be installed first and lightly tightened before installing the others. This ensures that the other holes (particularly the long one that goes directly into the block) are aligned. The theory of dowels is that they are installed first then during manufacture the other holes are drilled relative.
BTW one of my dowels was graunched after 50 years, and was able to make one from a 2" gr8 3/8 - 24 bolt with 1/2" trimmed off. The shaft is the same length as the original and only a 2 thou difference in diameter.
Also most of the torque is transmitted by the friction on the tightly compressed flanges hence the torque setting of 35ft lbs. I found this the most difficult task - access for a 1/2 torque wrench and getting enough movement without the car elevated to the heavens !
rg

 

[Bob_Spidell]

Bob,
Only yesterday I did this job. I am of the opinion that the dowel bolts are to locate the bell housing relative to the engine and so they should be installed first and lightly tightened before installing the others. This ensures that the other holes (particularly the long one that goes directly into the block) are aligned. The theory of dowels is that they are installed first then during manufacture the other holes are drilled relative.
BTW one of my dowels was graunched after 50 years, and was able to make one from a 2" gr8 3/8 - 24 bolt with 1/2" trimmed off. The shaft is the same length as the original and only a 2 thou difference in diameter.
Also most of the torque is transmitted by the friction on the tightly compressed flanges hence the torque setting of 35ft lbs. I found this the most difficult task - access for a 1/2 torque wrench and getting enough movement without the car elevated to the heavens !
rg

Logical enough, but why would it matter if the gearbox is installed a half-millimeter--or hundredth of a degree--one way or another relative to the engine plate (I'm with Healey Nut on this aspect)? The three components--block, plate and bellhousing--are under heavy shear forces during hard acceleration--and reverse, for that matter--and clamping force alone may not be adequate. I can't think of examples at the moment--splined shafts, maybe--but when shear forces are involved there is usually some sort of interlock mechanism to resist, as opposed to bolts in tension, which do not have to resist 'sideways' motion.

 

[red57]

I don't think it has as much to do with clamping forces as alignment of the pilot bearing & the input bearing in the trans. If all these bearings aren't properly aligned, there could be excessive/premature wear. Wheel lug nuts/bolts don't usually have dowels, driveshaft flanges don't have dowels, they rely on clamping forces to prevent 'fretting' and these would be some of this highest torsional loaded parts in the car. I don't really know how critical the bellhousing dowels are but I do think alignment was the original purpose.

 

[steveg]

I don't think it has as much to do with clamping forces as alignment of the pilot bearing & the input bearing in the trans. If all these bearings aren't properly aligned, there could be excessive/premature wear. Wheel lug nuts/bolts don't usually have dowels, driveshaft flanges don't have dowels, they rely on clamping forces to prevent 'fretting' and these would be some of this highest torsional loaded parts in the car. I don't really know how critical the bellhousing dowels are but I do think alignment was the original purpose.

I agree re the alignment. My Alfas had a couple of steel dowels on the back of the engine mating up to the bell housing.

 

[Bob_Spidell]

I don't think it has as much to do with clamping forces as alignment of the pilot bearing & the input bearing in the trans. If all these bearings aren't properly aligned, there could be excessive/premature wear. Wheel lug nuts/bolts don't usually have dowels, driveshaft flanges don't have dowels, they rely on clamping forces to prevent 'fretting' and these would be some of this highest torsional loaded parts in the car. I don't really know how critical the bellhousing dowels are but I do think alignment was the original purpose.

Makes sense.