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Re: Re: rough engine

actually I was wrong about the pistons, they're standard A7 type, so probably not terribly light. The valve springs are standard but doubled up with smaller ones inside. The inlet valves are a bit bigger, and the cam followers are flatter than standard. The head is from a late 30s rosengart (found in a french auto jumble)Not sure about the compression ratio though. The flywheel is slightly lightened.
I think the ignition timing is ok,it doesn't smooth out at all,even if you really retard it. Fuel's standard.
The engine's coming out at christmas, I think we'll try a standard head and lighter pistons and see what happens.
How much are Vince's gears? Have you got them in a mag or coil engine? mag engines have more and so seem to be more sensitive to worn gears.

Re: rough engine

Tom,

Most of your engine is the same spec as mine with the exception of the cam shaft and followers, mine are totally standard, I do have the oversize valves, double springs +80 JP pistons and a standard Austin high compression head.

My guess would still be that the combination of modified cam and flattened followers will be giving a 'bigger bang' (to put it crudely) in the engine which will do nothing to 'smooth' the running. When I upgraded my engine I noticed more engine noise particularly under load.

On my other car, similarly modified but only +40 pistons I found that the exhaust noise under the floor ( short chassis ) was excessive and have had to rubber mount the exhaust and use sound deadening material along the floor on that side of the car.

The downside of more power is usually more noise.

My enine is a coil engine.
Give Vince a ring on 01985 216632 I am sure he will be happy to sell you a set of gears.

Malcolm

Re: Re: rough engine

I think the confusion on page 137 is that the two drawings do not relate to each other. The drawing of the crankcase is only to show the position of the stamping mark of the deviation from standard- in this case the two holes are .0005 closer together than they should be to achieve a ‘standard’ fit.
The pair of gears are a separate item and show a .004 larger than standard gear mated to a standard gear. A.K. Georges crankcase was .0015 larger than standard, so when he fitted these two gears into his case he had a .0025 over meshing situation which broke the teeth.

Re: rough engine

Not meaning to be rude, Tom, but no chance the larger valves are just touching the head? Apologies if you have not fallen into this trap!

Did you have to skim the head, if so, how much? Highish cr could make it feel rough.

Otherwise - baffled!

Regards, Stuart

Re: Re: rough engine

i don't think the valves are touching the head, we machined away some of the ally using a flat ended blade in a wood router(!) to make sure there was enough clearence in each of the combustion chambers...
It's a pretty good way of machineing soft metals if you don't have a proper mill!
I agree that the flat tappets might be the problem, it'll be interesting to see what difference it makes. It's true that more power generally means more noise, maybe some ear muffs are the answer!

Re: rough engine

It look like you have plenty to "chew"on. Dare I ask at this late stage What sort of "rough" it is .Is it a running roughness or knock type . Tell us more about the carb. 30mm is really " fat" when you consider that standard is 17mm. For what it's worth I think the piston choice you have already made should be fine. Mac

Re: Re: rough engine

It feels like a normal car does when it is very over advanced (it isn't) it vibrates alot when it's idling and above 50mph it really feels as if it's going to shake itself to pieces. I know it's only an austin 7, but it's got all the right bits, so it should rev more than that!
As far as the carb goes, it probably is a bit big, but the choke tube is fairly small. I don't think that should cause roughness though, and they where standard fitment on ulsters. The carburation is generally ok - pick up is fine,and it doesn't use too much fuel.
I think I'll try standard cam followers first, and see what that does.

Re: Re: Re: rough engine

Tom

In your first post you mention that it has been balanced.
Please accept my apologies for seeming a little obvious, but I presume its all gone together in the same way as it was balanced? Mind you on saying that I suppose with keyways there isnt much scope for error.
I guess you have also checked all the usual things with respect to the bottom end? As Forum members may remember I have recently stripped an engine several times in an attempt to find an elusive "harshness", and several people advised me to check all manner of things like endfloat, flywheel runout etc etc. I have now given up and intend to try it on the road to see what it is like!
However on saying that, in your case you seem to be describing an engine that is running rough as oppossed to sounding a bit rough. It seems to be more fundamental, are you sure of the cam timing? I guess theres no chance of a grinding problem, maybe you could run it up on the rollers and check the ignition timing up through the rev range? You also mention that you are not sure of the compression ratio, There is some info on the net (maybe Bristol or Scottish site cant remember) about chamber volumes on various different heads, with our sidevalves this would be quite easy to check quite quickly

It would be great if you can cure it and then report back to the forum!!!!
Steve

Re: Re: Re: Re: rough engine

it's all food for thought. I'll tell you how i get on after it's all come to pieces....

Re: rough engine

Let's hope this is a 'pre-planned' parts seperation!

Cedric