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MGB Pitfalls and cans of worms regarding MGB flywheels

YakkoWarner

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I had to replace the starter on my car which has not run in many years - while I have the engine out I tested the starter with a fresh newly charged battery and while the solenoid moved the gear to the engaged position with much authority, the motor itself turned lethargically slow even while on the bench with no load. So I ordered a new starter, not completely unexpected. My question is on the flywheel - the ring gear has some slight wear but it doesn't look terrible. The clutch mating surface has some corrosion - it may clean up OK or there may be some pitting; I have not gotten to that yet. Since I'm replacing the starter I am considering simply replacing the flywheel, that way I get a fresh ring gear and a known good clutch mating surface and less chance of prematurely wearing out the brand new clutch pack I am going to install.

It LOOKS for all the world like you remove a handful of bolts and take the flywheel off. My suspicion is that this is deceptive. Do you have to open up the pan and start taking bearings apart to access the other side of those deceptive looking bolts? Does it have to be mirror-finish smooth? How will installing a new flywheel impact engine balance? Is this something I need to have an actual engine builder undertake to get right? Do I need to involve members of the clergy and hold rituals for successful outcome? I've never pulled one of these off before, I don't want to ruin the engine by getting it wrong.
 

Mickey Richaud

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Bolts are threaded into the crankshaft, so no worries there; no need to pull the pan. Before getting a new flywheel, you might take your old one to a machine shop and have it surfaced and balanced. And even if you get a new one, you might want to do the same. Mind the dowell pins - don't remember how many there are, maybe 2? And yes, the flywheel surface should be quite smooth.

Keep us posted.

Mickey
 

DrEntropy

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Should be six bolts, thin heads. Two locating dowels. There also should be lock-tabs on the bolts. Use only a six-point socket and be certain those tabs will not interfere with the fit of the socket on the bolt heads, they "round off" easily if the socket slips off repeatedly. Have the flywheel surfaced at a machine shop, and I'd suggest a new ring gear as well. New lock tabs are also a good idea. The used ones can weaken and break.
 
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YakkoWarner

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Appreciate the info - my PDF of a shop manual (which I found after posting the inital question) shows having to take the pan off and remove the crank bearings to get at bolts heads hidden inside; it suggests that the fasteners visible on the outside are nuts with bolts going thru a flange on the crankshaft? Is that only applicable to certain era engines? If they are just threaded in then bolts+lock tabs would be doable even by someone like me. I'll make sure I get a proper fitting socket if I attempt this - I've run into similar issues on vintage boat motors where a socket is slightly tapered at the end to make it go onto the hex head easily but on a thin head doesn't get enough grip. Grinding down a socket to get rid of that taper (so it fits clean all the way down) seemed to work - I'm not above buying a throwaway socket for that purpose.
 

DrEntropy

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Yakko said:
Grinding down a socket to get rid of that taper (so it fits clean all the way down) seemed to work - I'm not above buying a throwaway socket for that purpose.

Perfect!

No idea where the PDF you got cane from, but this is the back of an MGB block (pardon the dust 'n dirt!) showing the six threaded holes and pins. Flywheel removed. No need to drop the pan!
MGBcrank.JPG
 
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YakkoWarner

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Well that is encouraging for certain. Do you know which series engine that is (18GB, 18GH, 18V)? It may be they changed it earlier to later - the PDF I have is a scan of the MGB service manual (part #AKD 3259) from Leyland Cars itself. If I can figure out how I'll try to screen cap the relevant page so you can see what had me confused....
 

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YakkoWarner

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That didn't go exactly as planned but if you examine that PNG you can see that it shows bolts going into the crank holes from the inside, with nuts on the back of the flywheel. I'll examine mine real close; once real clean a magnifying glass should confirm I'm looking at bolt heads not nuts.
 

DrEntropy

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The photo I posted is an 18GB engine. Five main. You're looking at an MGA 1600 crank illustration. Unless someone swapped the B unit for an MGA one, you have bolts holding flywheel to crank.
 

LarryK

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Keep in mind,these cars were made for quick self repair on back roads and on track, can't fix quick if pan has to be removed to take off flywheel.
 
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YakkoWarner

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I took a good look at the back on my engine this weekend (unfortunately the car is 60 miles from my house - my friend is generously letting me use 1/2 of his garage since I don't the kind of income it would take to have a garage installed). The flywheel really looks like bolt heads not nuts, so it seems like the drawing is wrong even though it is in an MGB manual.
 

DrEntropy

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I took a good look at the back on my engine this weekend (unfortunately the car is 60 miles from my house - my friend is generously letting me use 1/2 of his garage since I don't the kind of income it would take to have a garage installed). The flywheel really looks like bolt heads not nuts, so it seems like the drawing is wrong even though it is in an MGB manual.
Just looked in the Bentley Press "Complete Official MGB" manual and that's got the same illustration. It's wrong, even though it shows the five-main crank. I'd never noticed that! I got that manual in 1969, just before purchase of my first MGB. I recall my dad and I pulled the engine & transmission to renew the clutch about a year later and decided to replace the ring gear at the same time. Must not have paid much attention to the crankshaft illustration!
A Haynes manual has only a drawing of a three-main crank but a photo of the back of the engine clearly shows nuts on the outside of the flywheel. All quite confusing. o_O
 

Mickey Richaud

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British sense of humor...
 

billspohn

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FYI the studs on the 3 main version of the engine are inserted from the back and would need removal of the oil pan if they were to be replaced, but one doesn't have to replace them just to swap flywheels so there should be no issue either way.

If the ring gear teeth are OK, I wouldn't bother swapping it.
 

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