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MG MGB Technical - Resurface flywheel?

Hello,
I'm a novice doing my first clutch change do to the addition of an overdrve transmission. I've got the engine and gearbox seperated and I'm wondering if I should have the flywheel resurfaced. It doesn't have any ridges or blueing but now has a small amount of surface rust due to sitting in the garage for two months. I've heard yes and no and I don't know which way to go as I sure would like to get this job completed this weekend when I have some help.

I would appreciate your opinions and if I do machine the flywheel I will be looking for a shop in the Hiram-Douglasville-Powder Springs area. How much should it cost?

Also I'm worried about reinstalling the flyweel wrong once I take it off and it is ready to go back on. Any techniques are appreciated.
TM Byers

TM,

Kind of hard to say without seeing it. It sounds like you may just need to clean it with sandpaper and a sanding block, or a jitterbug if you have one.

If you take the flywheel off, you might need to have a new bolt locking plate. The flywheel does have a proper orientation with respect to the crank (at least mine did), and there are some stamped numbers to identify the position. I can't remember the details with out referring to a book. If you have a Haynes manual, it's in there.

Charley
C R Huff

TM If its flat and smooth just sand paper to remove the surface rust.
DENIS4

Whenever I replace a clutch I follow 2 basic rules: Do not use rebuilt components and have the flywheel resurfaced. For $40 it is cheap insurance that the job is done properly the first time around. RAY
RAY

Some clutch suppliers will not entertain a warranty claim if the flywheel is not resurfaced.
David
David Overington

Thanks for the comments so far. TM
TM Byers

TM-
Although the hydraulic clutch mechanism is self-adjusting up to the limits of the original design specification, if too much material is machined away from the clutch friction surface of the flywheel, then the diaphragm springs will not be able to provide sufficient pressure. An original thickness lip should remain at the circumference of the flywheel in order to provide a stable mounting surface for the ring gear. No section of the flywheel should be less than a thickness of 7/16” (.4375”) and a 3/8” (.375”) radius should be used on all corners. After machining, the entire flywheel should be coated with WD-40 to prevent rust. When you are ready to install the clutch assembly onto the flywheel, clean the friction surface with alcohol.

All of the flywheels were stamped with a “¼” mark in order to ensure that the flywheel would be installed with the mark in a vertical position when cylinders #1 and #4 were at Top Dead Center so that the engine would be dynamically balanced correctly. It should be noted that the bolts holding the MGB flywheel to the crankshaft have significantly thinner heads than standard 3/4” bolts. Standard sockets have a tapered lip on the inner edge to help guide the socket over the bolt head. Unfortunately, this presents a significant problem in that the taper on the mouth of the socket does not allow a full engagement on the flywheel bolts, which in turn often results in damage to the flywheel bolt heads when attempting to remove or install them. The solution is to remove this tapered area and allow the socket to completely engage the bolt head. It should be noted that the flywheel bolts must be installed prior to placing the crankshaft in place in the engine block. Once the rear main bearing plate is in place, installation of these bolts is all but impossible. Flywheel bolts need only be torqued to their specified 40 Ft-lbs in order to prevent them from working loose. Flywheel loads are carried either by their shear pins or by side loads in the bolts; as such, they do not cause cyclic tension loads in the bolts.

While you have the flywheel off, inspect the teeth of its ring gear carefully. Do not be concerned if you notice that two sections of the gear teeth, 180° apart, exhibit more wear than the rest of the teeth. This is due to the fact that the engine tends to stop as either #1 or #4 cylinder attains compression, or as #2 or #3 cylinder attains compression. Ring gears for 18 GD and later engines (BMC Part # 12H 2900) should exhibit a notch machined into their teeth for the starter gear. These notches are preferable for longer starter gear life and less chance of the starter jamming in place and burning up. However, if the teeth are worn to the point that this groove is absent, or show a deep semicircular groove on the gear teeth of the ring gear (BMC Part # 1G 287) for the earlier flywheel for the 18G, 18GA or 18GB engines, then replacement of the ring gear is a fairly easy task. Cut the ring gear almost all the way through with a cutting wheel on a Dremel tool, or with a hacksaw, then crack the last 30 thou or so with a chisel. By using this technique, you will not nick the flywheel. Coat the flywheel with WD-40, seal it in plastic, the place it in a refrigerator or a deep freeze in order to shrink its diameter so that the ring gear will be easier to put in place. Heat the ring gear in an oven in order to expand its diameter so that it will be easier to put in place. Be aware that older cars had no step on the ring gear but some of the new replacements do. The step faces the rear for inertia starter motors. Note that the ring gear should not be heated above 250 degrees centigrade or the temper will be affected. Use heavy oven mitts, welding gloves or pliers to carry the hot ring gear to the flywheel. The heated ring gear should drop freely onto the wheel and should be spun immediately to make sure it seats on the flange. Allow the assembly to cool to room temperature and you are done!
Steve S.

I would take the flywheel to your local machine shop and get their opinion. I doubt if they would steer you wrong.
Tom

I have never had a problem and haver never needed to re-surface a flywheel. When you consider that on the MGB there is a hole to atmosphere designed in to allow oil out and you can drive your car out of the garage in the spring with the clutch as smooth as silk then it does seema bit of damp in the air is not going to upset these cars.
Stan Best

Steve S.

Please elaborate (he he, I'd say no problem there) on the following. I stuck my flywheel on after the crank was in.

Charley


"It should be noted that the flywheel bolts must be installed prior to placing the crankshaft in place in the engine block. Once the rear main bearing plate is in place, installation of these bolts is all but impossible."
C R Huff

Charley. I have, always, installed the flywheel after the back is installed. Very had to install the crankshaft, backplate, and flywheel as an assembly.

Sometimes, the fingers move faster than the brain.

I install the crankshaft, checking the main bearing clearances using Plasi-gage (sp?). Then, I install the back plate, lubricating the rear main oil seal. Then, I rotate the pistons until the number one piston is at, perceived, top dead center. At that point, I install the fly wheel with the 1/4 mark near the top. The 1/4 mark should be very close to being at the top. But, due to "dwell time" of the piston when at the top of its travel, there may be a few degrees of difference between the actual top dead center (unless indicated by a dial indicator) and the scribed line on the fly wheel.

As to the bolts having a shorter head than standard, and the problems of using a standard socket with them, I have offered, for several years now, a modified socket for this purpose. My website, www.custompistols.com/cars, has this available under the "tools" section.

Les
Les Bengtson

Clean it up with scotchbrite or emery. If it's not worn, blued or warped and has no surface cracks, that's all that is necessary.
Al

Charley-
Note that I said that you need to install the bolts, not the flywheel, prior to placing the crankshaft in place in the engine block.
Steve S.

Thanks to all that have posted. Tonight I cleaned up the flywheel with synthetic steel wool and proceded with the clutch install. I used the old bolts and one broke upon being torqued with the torque wrench. I now know to use new bolts and lockwashers for the next attempt (I feel silly).

Additionally one of the dowels is missing in the flywheel for the alignment. The other two are present so I'm guessing if the bolts are tightened to specification there shouldn't be an issue? What do you think?

I'm wondering if now that I'm back to where I've started if I should take the flywheel off and just go ahead and see what the machine shop says. The engine has average compression and will need to be rebuilt in the coming years so that is when I have planned to do everything above and beyond what is needed to just drive for a few years.

Any additional stuff I should know (such as use new hardware next time dummy)?

Just thought I would share my progress since everyone has been so kind to comment. This board is super helpful and I've been using the BBS archives a lot. If anyone is in the west metro Atlanta area and would like to get their hands dirty, send me an e-mail. I'm enjoying learning about working on these autos although it is frustrating at times! Thanks.
TMB
1970 MGB
TM Byers

This thread was discussed between 17/07/2008 and 21/07/2008

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