Fitting a duplex timing chain

[bmcecosse]

Yes - that's the idea. So - is there a lot of end-float on the camshaft ? The sprocket should assemble up on the cam shoulder - and then 'floats' with the triangular plate holding it fore and aft. Could be poorly machined camshaft I suppose.

[MarkyB]

Surely the only positive location of the cam happens at the front as the oil pump just pushes on?
I imagine the distributor drive impart a small amount of thrust but nothing else does.

Maybe making a shim for the crankshaft is a better solution, but something needs to be done to put it right, short of blue printing the engine.

[dellerie]

if these are helpful, then these are from when i did it

before











all fell into place for a novice like me

[bmcecosse]

Yes - the oil pump has no location function - it just gets driven round by the camshaft.

[mike-b]

Thanks for your photo's dellerie - it all looks very familiar to me by now!

Had another fiddle with it. I am sure that the cam sprocket is in the right position - when the cam is settled there is a very small (less than .5mm I think) gap, but the sprocket can be made to contact the triangular plate with a little presuasion (due to the endfloat in the camshaft. This is exactly what i'd expect, and certainly not what I'd call excessive end float.

There is a little end float in the crank as well (again fractions of a mm), and nowhere near enough to bring the sprockets into alignment. I measured the misalignment as 1.1mm, so I need a spacer of that thickness behind the crank sprocket to bring it up true. The workshop manual (page AA.20) seems to confirm that there should be packing washers behind the crank sprocket:

As the crankshaft gear wheel is withdrawn care mus be taken not to loose the packing washers immediately behind it. When reassembling, replace the same number of washers as found when dismantling unless new camshaft or crankshaft components have been fitted which will disturb the alignment of the two gear wheels.

I'm sure I didn't miss any when I took the old sprocket off, so I am wondering if someone has previously had it apart and not reassembled correctly. The fact that the crank nut locking washer wasn't the correct one (and wasn't actually locking anything!) hints at this.

[bmcecosse]

The crank shims would be retained by the key anyway. I've never seen more than ~ 10 thou shims there - but no reason why you shouldn't fit what you need - if that lines it all up.

[mike-b]

I know tolerances were a bit looser back in the 'good old days', but even so over 1mm is a bit excessive! I guess the reason will remain a mystery for now.

I'll try and find some suitable washers for the job then.

[bmcecosse]

I've never seen any 'bad tolerances' on any A series I have opened up - and never more than ~ 10 thou shims to line up the sprockets - always carefully done. I suspect something has worn in your engine - you don't mention crankshaft end float as a measured figure ? The thrust washers often take a beating on Minor engines - worth checking I think.

[chrisryder]

There is a little end float in the crank as well (again fractions of a mm)

[Alec]

Hello Mike,

a bit of a wild shot but could the thrusts have been assembled incorrectly, i.e all four on the back thrust face? I don't even know if it's possible and have the engine run OK, but that's about the thickness you are missing? You have nothing to lose by taking the sump off?

Alec

[MarkyB]

if someone has previously had it apart and not reassembled correctly.

I'd take that as read, very common to find lost or wrongly fitted washers etc after all these years.
Also I'd agree with Roy that is very rare to find an A series badly out of spec.

Do you have any history for the car? Even how many owners it's had would be interesting, as would contacting previous owners.

Friday afternoon cars probably got picked up by the dealer network quite early on and rectified, but if it wasn't used that much by someone a bit deaf maybe, then moved on to owners who got tired of replacing timing chains then moved it on, who knows?

Did the engine have a tendency to slow right down or stall when the clutch pedal was pressed?

[bmcecosse]

I would prefer to see a 'measured figure' - not just fractions etc. No Alec - the second row of thrusts would spin out immediately.
And the side with no thrusts present would immediately destroy both the crank and the block.........

[mike-b]

Not too sure on this car's history - I do have a pile of paperwork that came with it, but it had quite a bit of work done not too long before I bought it - mostly bodywork though. It had a respray and whoever reassembled the trim and panels seemed to use a random assortment of nuts and bolts! God help me if they ever did any mechanical stuff to it!

I've had it nearly three years and only driven it twice (first time was the 250 mile journey home with it, where things like windscreen wipers started falling off!), and the second was to take it to the nearest specialist for a valuation (for insurance). I got 8 miles and snapped a halfshaft! Recovered home and it hasn't moved for over 2 years! As far as I remember it idles fine with the clutch in.

I'd be surprised if it left the factory with the timing gears so far out of alignment, so I can only assume that it's happened sometime since. It must have been a real chain eater - there's a huge difference in the amount of slack between the old (simplex) timing chain and the new one.

Spoke to the parts department at Charles Ware's and they have 4 of the packing washer in stock - but all 4 only gave 0.75mm. So I managed to get hold of a regular washer of a suitable size and it is near enough spot on now.

I've got all the timing gear back together now, just the new water pump to go on, and I can hopefully move on to the other niggly faults. I hope I'm just being paranoid about the new countersunk screws coming undone, got them as tight as I could with the hex bit.

[bmcecosse]

And some Loctite I hope........

[Alec]

Hello BMCE,

the camshaft sprocket is home, there is minimal camshaft end float so the crank has to be back in the block and the only reference point is the thrust area. I don't believe for a minute the crank is wrong dimensionally.
If the thrust has been bodged for whatever reason, I don't accept your statement saying the block and crank would be instantly destroyed, as rearward thrust is minimal and from practical experience with Triumphs which have a habit of dropping thrust washers in the sump and motor on for many miles. yes the block and crank are rarely useable after many miles but that is the heavy forward thrust due to the clutch.

Mike, I would drop the sump, particularly as the engine is out of the car, it would only take a few minutes. As I said earlier there's no point compensating for an error, better to correct the error.

Alec

[les]

If you're happy with the assembly fair enough, but if you wish to explore more I can measure a genuine bmc duplex crankshaft gear for you, it could be that the kit you bought has a slightly shorter length gear. Of course it could be a thicker camshaft gear!

[taupe]

Am I missing something here???

The original sprockets fitted and were correctly aligned??

The new sprockets fitted the same way as the originals dont align... therefore the sprockets are wrong and should be sent back to the supplier for replacement.

Taupe

[chrisryder]

I put the original (simplex) sprockets back on to see what their alignment was like - and they are just as far out!

so it doesnt sound like the new parts are wrong.

[mike-b]

I'll be happy with the assembly if the engine works afterwards!

I didn't actually stop the check the old sprockets' alignment before removing, so it is possible that a washer/spacer came off and 'disappeared', but I think that's unlikely as I was quite careful and had a good look around afterwards. On refitting the old parts there is the same offset as the new ones have, so I can only presume that they were out of alignment too.

My engine is still in the car, and I don't really have any inclination to drop the sump at this point and start investigating further. My dad said the same thing as bmcecosse - if the thrusts were put in double together, one would just fall out.

Thanks les, for the offer to measure your genuine duplex gear, but as I've got it all assembled now, it's too late for me to measure mine. Unless I end up taking it all apart again...

[Alec]

Hello Mike,

I'm confused as the pictures show an engine on the floor not in a car?

Alec