Supercharging a Bagheera

[suffolkpete]

Could one use a 1.6 unevenly spaced crankshaft in the 1293 block?

Surely you'll just end up with 1592cc if you do that.  If  the 1.6 bore centres are different from the other blocks, I don't see how Spyros's idea, ingenious though it is, can be made to work.  Pity. such an oversquare engine would probably be very free-revving.

[Spyros]

Could one use a 1.6 unevenly spaced crankshaft in the 1293 block?

Surely you'll just end up with 1592cc if you do that.  If  the 1.6 bore centres are different from the other blocks, I don't see how Spyros's idea, ingenious though it is, can be made to work.  Pity. such an oversquare engine would probably be very free-revving.

No you can't use that crankshaft. No you won't get a 1592.

And sorry Pete, but this idea is not new.
Simply, up to know, the people who used the 1.6 piston also wanted to get this volume and so used the 1442 as a base.
Same stroke as the 1.6, so same volume.
Several people did it.

Here however, the idea is to use it on a shorter stroke engine. So not wanting the big volume.
Someone did it too, years ago.
Marcel Morel. He supercharge a Simca engine and since he wanted to compete in the 1600 class, he started also with a smaller engine. A 1100 cc. Why ? The stroke : 65.

[andyowl]

What a team! Thanks for all the thinking time!

Pictures from yesterday..

We have the blower bolted in and the general layout decided. I now know where the transfer shaft will go and I'm off to the bearing, belt, pulley and universal joint man this morning to order the parts.

I have spoken to the "Thick Head Gasket" man who is actually a "Decompression plate" man. He is quoting around 8 days for delivery and about the same price as I mentioned earlier. I will send him a new head gasket as a pattern today. The cylinder head is off and the engine looks in very good condition. I will check the valves and reassemble it with the decomp' plate when available.

We have taken the crankshaft pulley off ready to have the new pulley fitted. We made a special tool to stop the pulley rotating while we turned the securing bolt. Think of a long pair of scissors with M10 bolts welded on the tips of the blades. They go in the 10mm holes in the pulley and the handles of the "scissors" rest on the ground.

The old mechanical petrol pump is off and a blanking plate made to fill the hole. The new electric petrol pump will go close to the top of the tank.

This might actually happen!

We are using the existing 1442cc engine for the moment while we decide, with your help, which of the capacity options is easiest. The way the discussion is going suggests that re-grinding the crank-pins to give a 77mm stroke rather than the present 78mm might still be the easiest option. Finding (or making) shell bearings for 77mm will be the next problem!

Thanks again
Andy

[suffolkpete]

Could one use a 1.6 unevenly spaced crankshaft in the 1293 block?

I've just been reading the manual and I notice that, on the 1.6 at any rate, the piston centres are not in line with the con rod centres and that on the 1.6 two of the pistons have the opposite orientation to the other two, whereas on the smaller engines they all face the same way.  Perhaps this is how they obtain the uneven spacing, not by using an unevenly spaced crankshaft.  Would this mean that you could use a 1294 crank in a standard 1592 block, rather than trying to bore out a 1442?

[Spyros]

Pete,

The block you are speaking about are different.

The 1294 cranckshaft goes with a 1294 block
A 1440 or a 1590 block is about 1.5 cm taller. That's why it will not be possible to mix the taller engine part with the shorter one.
If you think about machining the top of the block, you can only remove about 1mm. After about 5, you are down in the water channels.

That's another argument for Andy to start with a 1290 cc engine : smaller push rods = less flexible = less weight and load on the valves = higher revs ! (again)

1440 and 1590 engines are also different and even between 1590 cc engines you have different types of blocks. The main difference for us, Bagheerian is that in order to fit (keep) our gearbox, you need to reposition 2 of the holding holes.

About the pistons, the 1590 cc pistons are not purely symetric. But, between the internal side of the pistons and the sides of the conrods, you have a play of 3,2 mm. Which let you recenter the conrod without problem.

If you want to start with a 1590 block, you will anyway start with a worn engine, and so also have to rebore it. Isn't it ?
Then, you will realize that you need a minimum of +0.4 overbore. Try to find them.
This only leave you to play with pistons of another french make that you'll have to adapt.
But then, it will give an even bigger cylinder capacity which is not what Andy want if he needs to stay in the same class

[andyowl]

Surprising developments....

When, on Sunday, I took the head off the current engine after I found that the engine was hard to start and was running very rough (after our track-day last week) I find that the cylinders are 80.6mm bore! Someone has already fitted a 1.6 engine! The cylinders are evenly spaced with around 9mm between each bore. The 1442 head gasket is assymetrical with a much larger gap between cylinders 2 and 3. The 1442 head gasket fits the head but does NOT fit the block! Maybe I have a 1442cc head on the 1592cc block?

The gasket metal ring in between 2 and 3 was not resting on the block metal. On the outer edges of #4 it was also not resting on the metal of the block. Hence the leak perhaps. The extreme activity at the trackday, plus the slight over-heating caused the gasket to leak I think.

I confess also that I did not check the valve clearences before I took the head off. It is possible that there was no valve clearence and maybe the valves became burnt at the track-day.

I have not had time yet to take the valves out - I have been busy again on the blower installation.

Either way I have ordered a Solara head gasket and I will report back on what we find. The Decomp Gasket man is waiting for a gasket to copy and I do not expect to receive it until Thursday. It was only while checking the 1442 head gasket I was going to send him that I noticed it did not fit the block! I do get some things right!

The capacity reduction to 1427cc will have to wait! 1592cc x 1.4 blower factor = 2.2 litres. Murenas better watch out! 

Andy

[suffolkpete]

The cylinders are evenly spaced with around 9mm between each bore.

That prompted me to go out and measure the 1.6 engine I am currently rebuilding and the bores are indeed evenly spaced.  So all that business about asymmetric pistons is to make the cylinders evenly spaced and the smaller engines are uneven, presumably to make room for the centre main bearing.  I suppose the bores 1/2 & 3/4 were too close together to bore out the 1.4  make 1.6, so they had to resort to the asymmetric pistons to even out the spacing. Fascinating!

[Spyros]

So all that business about asymmetric pistons is to make the cylinders evenly spaced and the smaller engines are uneven, presumably to make room for the centre main bearing.

Not really. On the uneven engine, in between cylinder 2 & 3, there is a water jacket.
This had to go to leave room for even spacing

  I suppose the bores 1/2 & 3/4 were too close together to bore out the 1.4  make 1.6, so they had to resort to the asymmetric pistons to even out the spacing. Fascinating!

They were not too close but the marging left would have mean no room for a rebore and potentialy a percentage of engines that could not have been fit for the bore.
Looking at all the evolution between the 1000 cc engine to the 1590 is indeed fascinating.

Andy,
There are no 1590 cc heads. These heads are identical to the 1440 cc engine 

[andyowl]

Spyros wrote...There are no 1590 cc heads. These heads are identical to the 1440 cc engine.

Thanks for that. I will not now need to take off the head from my Murena 1.6 engine!

It has always puzzled me that people claim that the Murena 1.6 engine was not much more powerful than the 1.4 Bagheera engine even with twin DCNF carbs fitted. Surely an extra 10% capacity should give around 8% more power? Why bother otherwise?

What can be done to the 1.4/1.6 head to improve it? Gas flowing would be a start but how much can be removed? Is there any experience out there?

The inlet ports look quite generous but the exhaust ports are skinny. Hard to see how the valves could be enlarged. They are very cose together.

I think I read somewhere that one should remove any sharp edges in the combustion chamber on a blown engine to minimise the risk of excessively hot corners causing pre-ignition. It would also make a small reduction in compression ratio. Probably worth a try while I have the head off.

Andy

[Spyros]

The torque of the 1.6 engine is much better.

If you want to fit bigger valves, you are limited by the space in between.
Except if you fit excentric valves guides.
In UK, you should have some facilities to find those for BL types of engines (BMC A, B or Standard). Moss had a special catalog for these

For the exhaust port, I would avoid to open it too much.
The scale at the exit of the head is there to prevent exhaust gas to go back into the compression chamber.
I would work on a better exhaust instead (I also have a DXF for the flange)

If you want to gas flow the inlets, start by matching the carbs, inlet manifold and head. Then, think about the holes for the push rods. It is easy to go too far and to end up into these holes.
I was thinking that gas flowing was more important for normaly aspirated engines ?

[suffolkpete]

1592cc x 1.4 blower factor = 2.2 litres. Murenas better watch out!

Before you get too carried away, are you sure the gearbox can take the power? Reading the other threads on this forum they seem a little fragile 

Peter (Murena owner)

[andyowl]

suffolkpete wrote.....Can it take the power, gearboxes seem a little fragile ?....

"I don't know" is the straight answer. I am working on the principle that the gearbox takes the 1.6 Murena power and most manufacturers build in a factor of safety which is unlikely to be less than 1.5. I'm looking to gain 50% in power which may therefore be OK. I don't know of any other way of finding out than trying it. How I drive it probably has as much influence on its survival as the outright power it transmits. I seem to be reasonably gentle with my cars and the recent broken diff was the first time I have knowingly broken anything (and I am not convinced that it was something I did then!).

I also have several used gearboxes in the loft which will act as back-up. The one in use now is a Talbot recon unit and just out of the wrapping paper.

Fingers crossed!

Andy

[andyowl]

What have I got in there?

Last night I checked the bore and stroke of the existing engine. Bore is certainly 80.6mm and the stroke seems to be 77.9mm. Both are as accurate as I can get with a non-digital vernier. It seems we have a Murena/Solara block of around 1590cc. In very good condition too.

I will take the head apart shortly and check out the valves etc. They might not be so good!

I was surprised to find at "top dead centre" that the tops of the pistons are 1.5mm below the top of the block, not flush with the top. Is this normal?

The pistons have slight recesses machined into their tops, I presume for the inlet and exhaust valves. Also normal? I don't have a Murena or Solara workshop manual. Maybe I should buy one!

Watch this space (I know you are and I take great encouragement from that. Thanks!)

Andy

[Spyros]

Hi Andy,

Yes, this is normal.
If you increase a bore, you have more volume and since the cylinder head are kept the same, the compression ratio is increased. I suppose that this is the way Talbot managed to keep the compression ratio to acceptable level.

I checked a 1.6 and a 1.2 engine that I have currently in work.
The 1590 have the pistons 1.5 mm below the top (It's currently a trial fit to take the VW valves prints and I'll machine the top of the block because I need to built up the compression ratio)
The 1200 have the pistons less than 0.5 mm below.

Regards,
Spyros

[andyowl]

Well, Baggy Joe made it to the NEC with the blower and all its drive shafts and pulleys in place. It is non-working and shown as a "work-in-progress". The grand design we had built on Sunday had to be modified as the support for the tensioning pulley and arm collided with the head!

I received back the cylinder head from the machine shop on Tuesday and spent most of Wednesday cleaning it and fitting it onto the block. There are no valves yet in place although they have been ground in and the seats recut. The head was slightly bent and it has been lightly skimmed.  This implied that the combustion chambers were of smaller capacity than usual and he measured the volume using oil and a pipette. The answer was that the combustion chambers are now 20mL each. I measured the volume above the piston at top-dead-centre and concluded it was 18mL. I gave these figures to the man making the de-compression plate and he calculated again the thickness of the de-comp plate. We are targeting a compression ratio of 8.4:1 being the Shorrock recommendation for competition and fast road work. The required thickness is now 2mm.  The plate arrived on Thursday morning a few minutes before I left for NEC. Good timing all round!

I have not seen the completed Matra stand but on the left we have the Greig Dalgleish beautifully restored Bagheera S1 in pale blue, then Baggy Joe low and scruffy in bright yellow but very much looking like a serious competition car (well I would say that wouldn't I?), then a newly restored and very pretty Rene Bonnet Djet (from the Bowman father and sons team) in silver with black stripes, the Tim Boyes Murena with the Ford Zetec 2Litre engine transplant also in bright yellow and finally the dark red 16L Murena from Titus. What a line-up!

See you on Sunday perhaps?

Andy Owler