Flywheel bolts

[52b3b Joe]

I've tried searching the forum but I haven't found what I'm looking for yet so here it is:

When I took the flywheel off my other engine (1955 Plymouth 230) I remember the bolts came through the block side of the crank. I couldn’t get one of them out so I waited until the crank was pulled. I ended up putting a rebuilt 230 Chrysler industrial in the truck that I found.

My question: Would it be ok to buy grade 8 shoulder bolts and just bolt it on putting the treads toward the block with nuts on the block side of the crank? Or am I missing something here?

[Dave72dt]

There's a difference in the shear strength between the shoulder of the bolt and the threads of the bolt. Putting them through from the crank side puts the shank in both the crank and the flywheel giving it the highest shear strength. Going through the flywheel into the crank places the shear point in the threads, a much weaker point.

[52b3b Joe]

Is there a way to get the bolts in with the crank in or do I need to pull the crank? I hope theres a way to not pull the crank...

[Dave72dt]

Probably need to drop the pan and the rear main cap unless there's a recess in the block that will allow a bolt to be inserted.

[52b3b Joe]

thats what I was affraid of...darn

[Don Coatney]

There's a difference in the shear strength between the shoulder of the bolt and the threads of the bolt. Putting them through from the crank side puts the shank in both the crank and the flywheel giving it the highest shear strength. Going through the flywheel into the crank places the shear point in the threads, a much weaker point.

Are you sure? The crankshaft flange is thicker than the flywheel flange. If you install the bolt head on the crankshaft side the shoulder will not catch both surfaces. I installed my flywheel shouldered bolts with the nuts on the engine side as pictured. I did this over 40,000 miles ago and no problems to date.

[Don Coatney]

Pictured below are the shoulder bolts I used. I did have to cut them to the correct length. I have several extras as I bought a full box. If you need some let me know.

[Dave72dt]

Are you sure? The crankshaft flange is thicker than the flywheel flange. If you install the bolt head on the crankshaft side the shoulder will not catch both surfaces. I installed my flywheel shouldered bolts with the nuts on the engine side as pictured. I did this over 40,000 miles ago and no problems to date.

I wouldn't have thought the flywheel to be that thin at the flange! Obviously it can be mounted with bolts coming through the flywheel first. Clearance between the nut and block must be really close. Shear point still needs to be in the shoulder area of the bolt. As long as that happens, it'll work either way. Thanks for the pictures.

[Merle Coggins]

If there is proper clamping force from the bolts than the shear force is negligible. Once the clamping force is gone all bets are off. It wouldn't matter which way the bolts are installed.

Merle

[Dave72dt]

From Don's pictures, it looks as if the nuts backed off even a little bit, there would be a clearance problem. I'd rather put the thinner bolt head on the block side as the thicker nut and washer. If it was strictly clamping force, there would be no need for the shoulders on the bolts. They must act somewhat as dowels also. Parts listing shows them coming in from the block side. I'd definitely use some Loctite on them if putting in from the flywheel side.

[Merle Coggins]

The shoulder helps with alignment during install and adds strength to the bolt.

Merle

[Dave72dt]

Usually there is a slight recess in the flywheel where it mounts to the crank to help with centering and the bolt holes usually have one that is off a bit from a true equi-distance pattern so the flywheel can only go on in one location to maintain balance. Are these flatheads set up that way? I have no personal experience with these particular engines but most other enginesare set up that way.

[Don Coatney]

The first picture better shows the thickness of the flywheel where the bolts go through. In an early mock up I did have the bolts installed with the nuts on the flywheel side as seen in the second picture. However another reason I installed the bolts with the nuts on the engine side is the rear main bearing must be removed (including oil pan removal) to remove the bolts if they are installed with the nuts on the flywheel side. Also note the center punch alignment marks I made. I did this because as has been mentioned the holes between the flywheel and crankshaft flange will only line up one way. And of interest I used a 4 bolt (Plymouth P-15) flywheel on a (Desoto engine) 8 bolt crankshaft. With this setup it was still true that the holes only line up one way.

I do not have a picture of the crankshaft flange on my Desoto engine. But I do have a picture (picture number 3) of the crankshaft flange on the Plymouth engine. Note that the nuts on the factory Plymouth engine go on the flywheel side. Also note that the factory bolts have a special head notched to fit the crankshaft shoulder so no wrench is required to hold them while torquing.

[Dave72dt]

Would the factory bolts, as in the last photo have been swedged to hold them tight in the crank flange, same as wheel bolts in an axle flange?

[Don Coatney]

Would the factory bolts, as in the last photo have been swedged to hold them tight in the crank flange, same as wheel bolts in an axle flange?

I dont recall and I no longer have that engine. But looking at the photo it appears the bolts are not flush with the flywheel.

[wayfarer]

Yet another 'mystery' from MotherMopar. All of the flywheels in my collection have a step on the trans side against which a oem clipped head shoulder bolt rests so that when tightening the nut, on the engine side, the bolt won't spin.

Using a 'normal' bolt would not allow for proper tightening unless the step was removed, ie. spot faced.