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MG TD TF 1500 - Flywheel pins

Just working on a friends XPAG fitting modern rear seal.
When we stripped it we took out the crank and flywheel as a unit.
After fitting the crank and seal we tried to replace the flywheel, NO GO. The locator pins in the fly wheel caused the flywheel to foul the casting, we had to remove the pins to get it in.
In the past 50 years I have worked on many XPAGs and never came across this.
Ray TF 2884
Ray Lee

Hi Ray,
My experience with MGs goes back all of 12 months but when I was researching the engine before the strip down I read somewhere that the crank and flywheel have to come out together. The contraption I am using to mount the engine on the stand would probably not allow me to do it any other way anyway.
The machinist who just balanced my crank/flywheel/pressure plate assembly had to make new dowel pins as they were a taper fit and offset so the flywheel can only fit in one position. One of the pins had been forced in and burred so that the flywheel could never have mated perfectly with the end of the crank - the joys of picking up the pieces after how many POs?
Which rear seal are you using? I am thinking of trying the build up of epoxy to restore the original clearance but haven’t seen any info on its long term effectiveness.
Chris
C I Twidle

Ray
I don't know if Xpag's are like this but on B series engines the flywheels are marked 1/4 and that mark has to be at the top when 1-4 are on tdc I've struck a few that must have slightly offset dowels which, if you go to fit the flywheel half a turn out, it simply won't fit on the centre properly, turn it half a turn and on they go--might be worth a try
willy
William Revit

Willy,
tried it in all positions and as I said I have done many over the years. The crank bolt holes are displaced to ensure the flywheel goes on in the right position.
I have compared the block to my spare and find that the casting varies, so maybe the sandcasting core was damaged, the difference is only about 1/16" but enough to make life awkward

Chris,
we are using a Moss conversion to a modern lip seal. When you do this you cannot fit the crank/flywheel as a unit. The flywheel has to be machined to clear when the seal is already in place.
Ray
Ray Lee

I'm reading quickly and may have missed your point - on re-assembly the flywheel is offered up to the crank (as above: offset holes; it only goes one way), with pins removed. The 4 bolts are snugged down by hand, the tapered pins are inserted and driven in to the flywheel and crank to firmly align the two, and then the bolts are torqued down to spec.

Sorry if I have mis-read.

Tom Lange
MGT Repair
t lange

Hi Tom,
No you have not missed the point, it is just that every other one I have done the flywheel comes in and out with the pins in, (but only just and with the pins horizontal)
I understand that the bolt holes are offset and the pins are only for alignment.
Ray
Ray Lee

I do think we are on the same page - a difference in procedure, but I think fitting the pins last gives better alignment with the flywheel.

Just to confuse matters, I usually drill out the dowel holes, tap the crank, and install two more bolts, for positive fit.

Best, Tom
t lange

Hi Tom,
The flywheel recess fits neatly over the brand new crankshaft so is located radially.

As you say the dowels are only to align the flywheel. If four 10mm bolts torqued up to 50ft/lb and lockwired won't hold it then two 8mm dowels certainly won't.
Ray

Ray Lee

Ray,

Hopefully, even if in your opinion the two dowel pins aren’t needed, you did replace them once you had the flywheel bolted in place. If you didn’t you’re going to have a tremendous oil leak thru those dowel holes that your new rear main seal won’t have any effect on. I hate to admit it but I am “the voice of experience”.

Gene
Gene Gillam

Thanks Gene,
I did know that the dowels have to be put back we have done a few of these mods.
Anybody doing this, you MUST use new flywheel bolts. Besides being good practice the original bolts will have stretched and may graunch into the new seal housing as the clearance is tight. Would be a good idea to check new bolt length as well.
I am very impressed by the new crank,EN408 billet steel,shot peened surface and mirror finish on the flange ready to take a lip seal.
Ray TF 2884
Ray Lee

Ah, Gene, that explains the taper fit!
On a similar theme I recently took my crank/flywheel/pressure plate to be balanced as a unit. The crank/flywheel balanced with minimum effort but when he added (what I assumed was the original) pressure plate the balance was out by nearly 90g in one position and double that when rotated 180o. The locating pins we’re causing the pressure plate to be none concentric with the flywheel. I wonder what it would have been like to drive?
Ray, do you always buy the ridiculously expensive OEM replacement bolts? I have been tempted by 12.9 rated replacements (originals were equivalent to 10.9) available quite cheaply online. Cross drilling the heads for wire has not proved to be difficult.
Chris.
C I Twidle

Chris,
we buy the bolts through the Octagon MG Car Club, not as expensive as other suppliers and keeps the club finances up.
Clutch assemblies are notoriously out of balance and the driven plate is only loosely
located by the bush and spline.
The pressure plate needs to be balanced with the crank/flywheel and trust to luck with the driven plate as it is never going to be in the same place twice.
Ray
Ray Lee

As best I can measure the holes in my flywheel, the dowels are slightly over 17/64" diameter, and do not appear tapered. However, they are not only for location - they transmit all the torque between the crank and the flywheel during drive, and the reverse during over-run. The four bolts do not do this as they run through clearance holes in the flywheel, even if the clearance is minimal - they only hold the flywheel to the flange on the crank. I have removed the four bolts from my engine, and after breaking the tightening torque from the original installation, the bolts undo easily, and the shanks show no signs of touching the sides of the clearance holes in the flywheel.
R A WILSON

I think those pins would not stand the torque reversals of our 54HP engines never mind the higher rated ones. when the pins are fitted they locate the flywheel centering the bolts. When tightened up the bolts lock it in place.
Modern engines do not have these locating pins as CNC machines are so accurate.
PS the pins are tapered
Ray
Ray Lee

I think you slightly missed the point R A W, when the four bolts are tightened they exert a considerable clamping force between the flywheel and crank. I initially assumed (without having the brain in gear) that the bolts, along with the dowels, would be experiencing a shear force but my assumption was quickly corrected by more experienced heads on the other forum. If the bolts were not under such high tensile loads then there wouldn't have been the necessity to specify high tensile bolts in the first place.
Chris
C I Twidle

The workshop manual and parts list calls them dowels, and they are parallel - as are the original dowels in my engine (and it is not a Morris or BMC reconditioned engine).
Doing up the bolts tight will ensure friction between the flywheel and the crankshaft flange, but this friction is at a very small radius and would easily be overcome by the torque of the engine and the large diameter resistance of the clutch (when in gear) - if it were not for the dowels. As there is clearance around the bolts, however minimal, but no clearance around the dowels, the torque must be taken up by the dowels, with assistance from the above mentioned friction.
I do not think the original bolts were HT as it is possible to file the heads, and I still use my original bolts, with no clutch or flywheel problems.
However, everyone must do as they think.
R A WILSON

I'm using a new crankshaft that takes ARP small block Chevy sized bolts but I somehow still managed to shear off a couple flywheel bolts and the dowels. I was using an aluminum flywheel and I think the bolts lost torque through deforming the aluminum slightly. I had hardened seats installed in the flywheel to prevent further issues. I've also had a clutch locating dowel come free and do significant damage bouncing around in the clutch.
Use the best bolts you can find.
Kurt Byrnes

I would be interested in the views of the forum on increasing to 6 bolts.

Some of the lightweight flywheels available (eg B&G) are already pre-drilled this way.

Michael
M R Calvert

Chris,
You suggested that the flywheel bolts are subject to a shear load. The actual purpose of these bolts is to provide sufficient clamping force to assure that the bolts are NOT in shear. Indeed, with the right torque, they clamp the flywheel and crank together so tightly that the bolted joint's friction takes all the shear. Furthermore, if there is any load that the clamped joint can't handle, the dowel pins are there as back-up.
Many engineers have had expensive and embarrassing design failures due to their flawed analysis of bolted joints. Some of their case histories make very interesting reading.
Ed

I don't know Ed but this was the reply I got on the other forum when I somewhat flippantly suggested that the bolts where in shear.

Pins quite probably parallel, the machinist said they looked to have been tapered and I took him at his word. It crossed my mind that if they had been tapered the taper might have been distorted to parallel by use. The original bolts were rated at "V" class which is roughly equivalent to metric "10.9" class. I am currently waiting for delivery of some 12.9 class bolts from PRC which, provided I can cross drill them as easily as the 10.9 hex cap screws that I found locally, I intend using. The cap screws would probably have been strong enough but the load bearing surface under the head was quite a bit smaller than the original head bolts despite there being a circular area under the hex.

A very rough mental estimate suggests that, ignoring the possible extra strength of the bolts over the pins, the pins could contribute around 10% to the area of material if it were simply in shear.
Chris
C I Twidle

It is the clamping force that handles the torque. The next joint down the line is the U/J flange which in top gear handles exactly the same torsional load. Those bolts are always loose in the holes when dismantled proving to me that they take no shear load.
Ray
Ray Lee

I apologise.
The pins are parallel, just checked on an unbutchered flywheel.
I presumed they were tapered as it is good practice to have parallel pins only into blind holes to prevent accidental release into other parts.
Ray
Ray Lee

This thread was discussed between 19/12/2017 and 22/12/2017

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