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MG MGB Technical - clutch alignment tool diameter too big- help

I purchased a 5 main engine that came from a 67B (that the owner said ran great) to swap with my engine for my 76B which died. Before swaping the engines, I invested in a new clutch. When trying to install the new clutch, I discovered that the diameter on the clutch alignment tool (purchased from Moss Motors) was too large to fit into the hole in the flywheel.
Does anyone have any ideas as to why? Is the diameter of the shaft for 3 main engines smaller than for 5 main? If so- I suspect, the engine I have is from a 3 main and my tranny shaft will not fit into the corresponding hole inte the flywheel. Any ideas on what I shoudl do next?
Bud
Charles Yanak

Bud,
The early 3 main bearing engines, 18G and 18GA, used the smaller first motion shaft. You might be able to change the spigot bushing to the later type to get your's to fit. Check the Archive section for more information.
Tony
Tony Shoviak

Bud,
You will have to look into changing the rear backing plate to get everything to work. I don't think it's a straight up swap.
Tony
Tony Shoviak

Bud. As Tony has noted, the 1967 engine is, most probably, from a Mark I MGB. In very late 1967, the four syncro transmission was introduced which had a larger first motion shaft (input shaft) nose than the three syncro transmissions did. All of the MGB clutches interchange, but you have to use the correct clutch alignment tool and transmission with the clutch installation.

Unfortunately, there seems to be a miss-match here which will have to be corrected before you can use the new engine in your car. One of several you are going to find as you progress.

The pilot bushing may have to be custom made. Moss Motors lists a "Bushing, spigot, 1-1/2" long", part number 330-570 and notes it is for a "5 main/3 main conversion"--but it does not tell us if that will allow us to use a five main bearing engine, designed for use with a three syncro transmission with a four syncro transmission. If you can remove the existing pilot bearing and measure the outside diameter and length, we can compare those measurements with the Mark II and later pilot bushings and come to some form of understanding. (There is a tech article on the MG section of my website showing how to remove and replace the pilot bushing--www.custompistols.com/.)

Again, as Tony notes, the engine back plate will have to be replaced as both the starter positioning and the pattern of the transmission to engine bolts are not the same between the 67 and the Mark II and later engines.

As has not been noted yet, the front plate will also have to be changed out as, when the rubber bumper design was introduced, the design and position of the motor mounts was changed.

The above are the basic changes you will have to make if you want to use the 67 engine. But, there are more changes which would be desirable to make.

First, the timing chain cover and harmonic balancer. The 67 engine has the timing marks located on the bottom of the timing chain cover and the harmonic balancer is set up to work with that system. Your current engine, then 18V was used from about 71 until the engine of production, has the timing marks located on the upper right (when viewed while seated in the driver's seat) section of the timing chain cover and the harmonic balancer is set up to work with that position. The latter is far more convenient for dynamic timing than the former. Since you would have to remove the timing chain cover, along with the timing chain, timing chain tensioner and the crankshaft and camshaft sprockets before you can remove the engine front plate, you might as well change over to the latter timing chain cover and harmonic balancer when you do so. Good idea to replace the timing chain and timing chain tensioner when you reassemble the system. (As a side note, do not replace the camshaft sprocket with a new one. Several years ago I informed Moss Motors, in writing, that the new duplex camshaft sprockets were incorrectly manufactured and were binding when tightened down due to insufficient clearance. These incorrect parts are still being sold by a number of sources and, to my best knowledge, no one is selling the correctly machined parts at this time unless they are selling used parts. So, keep the duplex timing chain, but use your old camshaft sprocket with it. The new crankshaft sprockets are good.)

Oil filter system. The 67 would have a hanging oil filter of the replaceable cartridge type. Your 76 would have the inverted can type oil filter--a one piece assembly that just screws onto the oil filter adapter. If you have never changed out the cartridge type oil filter, it is worth doing once in one's life to allow one to understand how poor a system it is. But, it is, also, not any form of fun to have to change out the old oil filter system for the 18V system when the engine is installed. So, replace the 67 with your 18V oil filter adapter before installing the engine into the engine bay and try to find a friend who has the old system and will allow you to change his oil for him.

In addition to the things you will have to change, if you are to use the 67 engine in your 76, there are some basic things which need to be checked out before installing an unknown engine into a car.

Rod and main bearings need to be checked and should be replaced unless you can document that has been done recently.

Tappets need to be inspected for condition as does the camshaft lobes. Check the pads and tightness of the rocker arms on their shaft at the same time. Check the pushrods for straightness. (And note that the tappets and pushrods are different than on your 18V engine.)

Cylinder head should be checked for straightness and crack inspected. Spare engines are not all that hard to find and may be purchased for a reasonable amount of money. Good used cylinder heads are becoming uncommon and are demanding a premium price.

Good idea to replace the core plugs/freeze plugs on an engine that is in unknown condition. They can be rusted out inside with only a quite thin layer of metal on the inside. When the newly installed engine is first started and the cooling system pressurizes, leaking can occur. (Remember, your 76 cooling system operates at a higher pressure than the 67 cooling system did and, even if the engine was running properly in the 67 when removed, the increased cooling system pressure could cause a leak if the core plugs are not in good condition and well seated. Replacing core plugs with the engine installed, especially the one at the rear of the engine, is even more fun than changing the oil with a cartridge type oil filter system.)

I do not know what was wrong with your 76 engine that required replacement, so can offer up little valid advise. But, I prefer, whenever possible, to rebuild the existing engine, knowing (hopefully) what I have when I am done and knowing that the work was done in a competent manner. I only replace the engine as a last resort. As you can see, replacement engines, unless you know exactly what you have and what you are doing, can be an adventure.

Les
Les Bengtson

Bud,
You say you SUSPECT the engine is a 3-main. It could also be a 5-bearing which has had the smaller spigot bush fitted to suit an early gearbox.
You can make sure by looking to see if it has a tachometer drive.

Regards,
David
David Overington

You didn't say if the clutch tool matches your gearbox shaft. I assume it does. Measure up the crankshaft bore and the gearbox shaft dia and see if it is possible to ream out the bush. If so, get the bush out (plunger and grease trick) and have it machined.
Art Pearse

The later spigot bearing fits in a larger hole in the back of the crank - no good reaming the smaller bush, the crank needs to come out and be machined to take the larger spigot bearing.
Chris at Octarine Services

Charles:as suggestions get tossed out on what to do and how to do it , I tend to think the first question that has to be asked is what do you want out of this
car?For the purpose of our discussion I'll jump right in and assume you are building a DRIVER and not a show car, and while you are not broke you have some kind of budget for getting this B back on the road.If I am correct, I can at least save you a little time and money.Rather then change the crank, change the input shaft or better said have it ground down to the correct size so it fits in the smaller bushing.As you move forward you will identify other problems bring them up and someone will have a fix. Until that time.Ric
RIC LLOYD

Charles-
The bush & trans input shaft size changed with the intro of the 5 main engine ('65), still with the 3 synch gbx. As David O said, it could be a 5 main with the reducing bush that makes it fit a 3 main 3 synch box; or, it could be a 3 main (or an MGA!). Again per David, if it has a tach drive at the back LH side of the block, it's a 3 main or MGA. MGA will have 1500 or 1600 cast in the side of the block; Engine # for 3 main MGB are 18G/18GA; 5 main is 18GB until '68, when the 4 synch box was fitted. After that it progresses up the alphabet as 18G*, then changes to 18V**. As Chris said, the 3 main crank won't take the bigger ID bush, and I don't think there is room to make a special bush for it.
You cannot change the input shaft, since there isn't a small pilot shaft for the 4 synch box, and machining it means total dismantle of your gbx and non standard parts.
My suggestion, if it is a 3 main, is to sell it off and get an 18V.
Where in Pa are you? Probably the other end from me, I am NW corner.

FRM
FR Millmore

I have a friend who lives in rural PA and owns a '64 Iris blue B. After driving my '67 that is fitted with a 4 synchro od trans, he wanted one in his 3 main '64. A local shop was able to oversize the spigot bearing hole in the crank while it was still in the engine. They also located and installed a 4 synchro od trans and it has never given him any problems. RAY
rjm RAY

Ray
You cant fit a 4 synchro box onto a 3 bearing engine as the crank doesnt have a rear seal(its a worm drive)so you cant fit a 4 synchro backplate on it so the engine must have been a 5 bearing engine as you can fit the 4 synchro back plate to this engine with no trouble.

Ste
Ste Brown

Charles:Having done it multiple times I can say with 100% certainity you can install a 4sp sychro on a 3 main engine.Transmission disassembly is not nessesary for removal of the input shaft.You will have to use the old style starter,modify the trans bellhouseing for starter instalation,install a stud in the engine plate to mount the starter and probably one or two things i've forgotten, it can be done! keep us informed. RIC
RIC LLOYD

Ric's method was what was done to my friend's car. It still has the original ineritia starter. A hole was cut in the bell housing to accomadate the starter. The mechanic used the original backplate. RAY
rjm RAY

This thread was discussed between 11/10/2009 and 16/10/2009

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