cracked engine back plate

[ian.mcdougall]

Hi all.
Engine out for clutch replacement and while its out decided to change oil pump. When removing engine i found that the top section of the bell housing was broken off so three top bolts not in use. Took the clutch off and flywheel, cleaned off the back plate to remove accumulated oil and crud and found a crack through the solid steel back plate from l/h side right through to the starter hole (so that's why oil leak from rear of engine). Is this a normal problem with the solid steel back plates or is it a consequence of the missing bell housing section.
Regards Ian

[jagnut66]

Hi,
What size engine is it, as I have a spare 948 engine back plate, if that's any good.
Never heard of one cracking before though!
Best wishes,
Mike.

[ian.mcdougall]

Thanks for the offer jagnut but located in Ireland. Engine size 1098. i have a spare 948 engine and smooth case box but the back plate is a pressed steel one and not solid steel. I have a traveller for spares for a back plate and box ( box of unknown condition), but its difficult to get at at the moment so ordered a secondhand one from bull motif as well as the oil pump, gaskets and a rad. I could get the gearbox out of the spare trav but i did want to get the other trav back on the road quickly but just wondering if the back plate will crack again quickly or be ok for the odd trip to shows etc.
Regards Ian

[philthehill]

Cracking of the 1098cc rear engine plate and the 948cc engine plate is rare but not unknown.
The 1275cc on the other hand is known to crack between the oil pump and crankshaft apertures.
A possible cause of the 1098cc rear engine plate fracturing is that the rear face of the block and the front face of the engine plate was not clean and when tightened stress was induced into the plate and eventually it cracked.
If the top half of the plate cracked the stress that caused the rear plate to crack could be then transferred to the gearbox causing the top part of the gearbox to crack and fail.
Another cause could be the two dowels aligning the gearbox to the rear engine plate were not fitted/fitting as they should and the gearbox was not fully home against the rear engine plate even though the bolts appeared tight.
The rear engine plate bolts may not have all been tightened to the same torque and so induced a bending of the rear engine plate.
It is important that the gearbox bell housing is whole when bolted to the engine as the gearbox alignment dowels which hold the gearbox in its correct alignment to the engine cannot hold that alignment if one is missing or unable to be used because the top of the gearbox bell housing is broken away.
Whilst it is up to you if you use the gearbox with the top dowel/bolts deficient I personally would not do so as you are inducing stress into the gearbox casing and just relying on the remaining bell housing bolts to hold the alignment which they will not do as they are not fitted bolts (sized for the hole).

[ian.mcdougall]

So it looks like a removal of engine and box from spares trav, remove gearbox check and clean, fit put in car and hope its OK. Its funny how a simple clutch change can escalate to major work. The top section of gearbox housing was not on the car, so i think that someone refitted gearbox in the past after breaking it off

[ian.mcdougall]

Update
Box out of car and cleaned up.Photos of damage. It looks like the top flange has broken off with 3 bolt holes and locating hole missing,i have an old engine and smooth case box i was given, the box was full of water. My idea is to cut off the section needed and take into work and weld it on,do i trim just the flange needed or make the piece larger to make a stronger weld.
also when i removed the gear lever there was no anti rattle plunger and spring in the holding cap,would there be a chance that it is lodged in the remote ?
Is the box made of a common aluminium, aluminium alloy or a weird alloy ?

gearbox damage

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gearbox damage

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[les]

Is it worth it? The alignment has to be spot on and the flange face perfectly flat, or you risk another stress fracture.
Your call but I'd have to get another case.

[philthehill]

If you are going to weld and I do not see any problem with that - remove the rear engine plate from the engine and bolt to the front of the gearbox and then bolt the replacement flange to the rear engine plate with the top dowel in place - that way it will all be kept true.

Try welding a section of the old smooth gearbox to get the welding rods correct and to see how the alloy welds before attempting the ribbed gearbox repair.

I am not aware that the alloy gearbox casing is anything special as regards the alloy. Many of the first gearbox conversions used a cut and shut Minor bell housing welded to whatever alloy cased gearbox was being used.

With care you should have no problems - just make sure that the front face of the bell housing is true - good luck.

Phil

[ian.mcdougall]

Hi Phil
I was thinking about using a back plate as a pattern to align the pieces for welding using the old back plate and using some box or angle iron to counter any distortion.I will be using a 3 phase mig with an aluminium gun at work, and also cutting some extra sections to practice on as i have more time using steel mig on cars but not so much with aluminium . Will report back when the welding is done.
Hi Les
Living in the west of Ireland it is harder to source second hand spares and to have them shipped from England is expensive.
Any answers on where the anti rattle spring and pin may be lodged , can they get into gearbox or are they likely to be in tail shaft.
Regards Ian

[les]

Fair enough Ian, good luck with it.

[ian.mcdougall]

Hi all
I have done the welding on the gearbox and fitted all lined up OK

Cracked back plate

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Welded bell housing

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Welded bell housing

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Gearbox attached with all bolts this time and secondhand back plate fitted

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Donor box

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donor box

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[philthehill]

Very well done

[RobThomas]

I've an idea that it is Qualcast Birmidal LM8 which nowadays equates to LM25, but I may be wrong.

[philthehill]

http://www.hadleighcastings.com/uploads ... Detail.pdf

The CS Autoclassics Ford conversion bell housing fitted to my Minor is cast in LM25 alloy.

[les]

Very neat, you've made a nice job of that.

[ian.mcdougall]

Thanks
It helps when you have access to a decent welder, took a while to dress the welds to shape with an angle grinder and small air finger belt file, still not sure which cracked first box or back plate, the broken piece of the box was not on engine, so i assume the box may have been damaged when clutch changed and then fitted which caused the back plate to crack, so unless someone had a similar problem we will never know.

[philthehill]

Ian
You will note that the crack runs along or below the rear engine plate mounting plate bolts.
With the top gearbox bolts not being in place the gearbox will flex the rear engine plate along that line.
Whilst the plate may appear to be solid it has no strength to resist flexing.
In my opinion the cause of the rear plate flexing and therefore leading to the cracking was the lack of top bolts holding the gearbox to the top of the engine.
Phil