Aprilia engine rebuild.

[stanley sweet]

Love it !

How much vibration is there ? I had this feeling that test-bench set ups are vicious and uncouth but I would love to try one and am now inspired !

Re "wind-up" ,  I have an engine in bits and will look.

Re carb problem - more details please

Is there any reason why rubber mounts couldn't be fitted to soften it?

[lancialulu]

Is there any reason why rubber mounts couldn't be fitted to soften it?

Aprilia engine is so sweet it does not need it. A gamma on the other hand on start up would rip the wooden structure to matchwood!! (Even with rubber mountings!).

[ben]

  The Aprilia engine is indeed smooth but interestingly it is on rubber mounts all-be-it quite small and therefore stiff ones. They are visible in the test-bed picture and are in series with the triple leaf springs.
  I have now reset the tensioner spring using one complete turn of wind-up and it seems to have cured the chain whip.

  The carb proplem referred to previously was due to an air leak between the float-chamber and the carb body.This is the standard Zenith which has a poor design feature in this respect.The float chamber is held in place by two vertical screws holding the chamber up against the lid which is integral with the body but it also has to seat tightly against the vertical face.On my carb the two faces were not exactly ar right-angles.The screws ensure a good seal between the bowl and the lid but a leakage gap was unavoidable where the jet feeds into the venturi. Hence the engine would run but was too lean to idle.
  The rather poor photo shows the metal strap I fabricated to hold the bowl side against the main body. Instant gasket was used to seal the lid and the screws were tightened with minimal torque.
   The long term solution could be;
                        make a thin wedge shaped gasket to get the faces at right-angle. (V Tricky)
                        machine the carb to correct the angle  (Also V Tricky)
                        bend the carb lid down to correct the angle---anyone tried to bend mazac(?)
                        scrap the carb and find another one.  Any offers?

   There was another problem that the test bed revealed which I had forgotten about when I posted the original story.
   After fitting the radiator and water pump both of which required lots of fettling to get them watertight I filled up with water and left it overnight. Trying the first proper start-up the next day I was surprised at how much top-up was needed but the engine did start and ran although would not idle as described before. What was less satisfactory was the amount of water that emerged from the exhaust!!!
    The first suspect was the head-gasket and the first step to removing the head was to remove the manifolds.
    When I removed the exhaust manifold i noticed water dripping from the No 2 exhaust port.I was still thinking the head gasket was leaking but when I got the head off there was no obvious sign of a problem and also there was no water in any of the cylinders.
    I will leave you to ponder on this mystery until I have taken some more pictures to post.
    Meanwhile back to the wounded carburettor!   

[nistri]

Thank you for  the very interesting info. Just for the record, is it OK to re-use copper head gaskets?
Regards, Andrea

[simonandjuliet]

Fascinating !

Couple of questions/points. It looks like you are running the engine with the cut-away rocker cover fitted, how much oil gets thrown around ?

Re carb, I am not sure I would try bending mazak, it is such an unfriendly material. I have found that plastic metal sticks very well to it , maybe you could build it up and machine the plastic metal ?

Re water leak, have you got a crack in the head around one of the internal exhaust castings ?

When refitting your headgaskets, do you soak them before re-using? I know there are mixed views about this, but I have often re-used the copper/asbestos gaskets without problems, but have always left them in a bowl of water for a day beforehand. What is the state of the central stud post ? They can be very messy !

Good luck with the carb and if you want a new headgasket I can help out ...

[the.cern]

Picking up on a couple of points ...

I agree with you Simon about bending mazak, I have never been successful no matter how careful I think I have been .... and I have found there is absolutely no warning for the point of failure!!!

Simon, I have not heard that tip for re-using copper/asbestos gaskets, but I will certainly use it.

Andrea, I have no experience of this, but understand that copper head gaskets may be re-used. It is advisable to anneal them first.

Ben, I love the 'repair' of the carburettor. That is a real engineering solution to overcome an inherent design fault.

                                 Andy

[ben]

 Back in 2008 there were a lengthy series of posts, started by David Laver, about the two types of inlet manifold found on Aprilias and the provision for pre-heating either with exhaust or water.It was generally concluded that the use of exhaust gas was perhaps only featured as an experiment or only on very early cars before the water-jacketed manifolds we are familiar with were introduced. However all the cylinder heads that I have looked at have the entry "port" into the "cast in" transfer passage filled with some sort of compound to blank it off.
For the engine I have on test I had cleaned out this material to open up the passageway.In practice I did not expect it to make any difference because the port is still blanked off by the head gasket.
The first two photo's show this.   

[ben]

Sorry,pressed "posr" by mistake!

[ben]

On the face of it if one wanted to feed water through this channel to the manifold one would need to make a hole in the gasket adjacent to the central stud to let the water in.
On my engine although I had not made such a hole the water did get into the transfer passage because the gasket is unsupported on the other side at that position which allows it to bulge down into the block. (See next picture)

One would expect this water to merely feed into the cooling chamber in the manifold.

However this is where we finally get to the interesting bit. After 50 years of ignorance I have discovered*****

THERE IS A FEED HOLE FROM NO.2 EXHAUST PORT INTO THE TRANSFER PASSAGE.

I have marked it with a blob of white Tippex in the last photo.

And of course that is why the water in my engine ran out of the No 2 exhaust port and filled up the silencer!

So it would seem that inlet manifold heating using exhaust gas is and always has been a feature or all(?) Aprilia engines! Both cylinder heads that I have been able to check have this feature and I believe one is early and one is late.
Just how much good it does is open to speculation o course but it seems significant that the feature was carried over when the manifold design changed from square to round.In fact as the inlet port sizes are more or less the same on both manifolds the main reason to introduce the round type was presumably to make the heating more efficient.
As far as I can judge this heating is purely to avoid icing up although the heat has to migrate up into the carburettor to achieve this.

[ben]

And to respond to the point about gasket re-use I have certainly re-used the same one up to 3 or 4 times on a standard engine---usually with a smear of red Hermatite.  Nowadays it would be Hylomar I guess.
With my raised compression ratio I might use the annealing and soaking tricks .
And I have a new spare just in case thank you Simon.

Regarding the query about oil splashing with my cut-away rocker cover, at idle there is no problem, but a certain amount of mist is spread around when the revs are increased.

After re-setting the spring tension for the timing chain I ran the engine without the front cover back on but that led to quite a severe loss of oil.Of course there was still no water in it at that stage so it was only a brief run---but long enough to see that the timing chain whip had gone away.

[simonandjuliet]

I will check my spare heads tomorrow and see if they are the same..... but all very interesting

[ben]

Hi Simon
            Note that when you check your heads the cylinder and exhaust port that I refer to as No 2 is the second from the front (which is No 1 cylinder in Lancia's "round the block" firing cylinder order!).

[Dilambdaman]

Certainly seems to have been something favoured by Lancia as it is found on the Dilambda.

An alloy cast box is fitted between the carb and the block with two internal passages to take fuel to the inlet valves. The space surrounding these passages is connected by a small bore pipe to the exhaust manifold allowing the exhaust gasses to warm the fuel mixture. The box has a water drain off tap and on the S2 a take off for the brake servo.

In use the alloy corroded badly and somewhere, although I can't locate it to photograph, I have one that came in completely wrecked state with Modestine. All of the Dilambdas that I have seen to date have had the pipe removed and the holes in manifold and box blocked. General consensus seems to be that modern day fuels don't need warming to perform well.

Robin

[simonandjuliet]

DiLambdas are complicated beasts !

[davidwheeler]

On the face of it if one wanted to feed water through this channel to the manifold one would need to make a hole in the gasket adjacent to the central stud to let the water in.
On my engine although I had not made such a hole the water did get into the transfer passage because the gasket is unsupported on the other side at that position which allows it to bulge down into the block. (See next picture)

One would expect this water to merely feed into the cooling chamber in the manifold.

However this is where we finally get to the interesting bit. After 50 years of ignorance I have discovered*****

THERE IS A FEED HOLE FROM NO.2 EXHAUST PORT INTO THE TRANSFER PASSAGE.

I have marked it with a blob of white Tippex in the last photo.

And of course that is why the water in my engine ran out of the No 2 exhaust port and filled up the silencer!

So it would seem that inlet manifold heating using exhaust gas is and always has been a feature or all(?) Aprilia engines! Both cylinder heads that I have been able to check have this feature and I believe one is early and one is late.
Just how much good it does is open to speculation o course but it seems significant that the feature was carried over when the manifold design changed from square to round.In fact as the inlet port sizes are more or less the same on both manifolds the main reason to introduce the round type was presumably to make the heating more efficient.
As far as I can judge this heating is purely to avoid icing up although the heat has to migrate up into the carburettor to achieve this.

Well, that solves a 40 year old conundrum.     I bought a series 2 "Nardi" engine from Julian Bolton who had taken it out of a convertible and put it into his 'Nash.    When I put it together, water poured out of the exhaust so I replaced the head with a new one I had bought from Cavallitto in 1971 on my first Lambda trip.    This does not leak, I know not why and I am not going to look as the car is going well.   I have just looked at the "Nardi" head and it has the passage from No 2 port to the transfer channel.   You now have the block from that motor.   I now wonder if there is any difference between a Nardi head and a standard one???

The Lambda is much simpler - just site the carburettor between the branches of the exhaust manifold and hope it does not leak too much!