i've just finished building a gordon england cup model replica. The engine is overbored to +80 thou with (I think) Honda generator pistons. It goes well and has stacks of torque but is really rough, especially when you rev it - compared to our standard chummy. Is this a natural consequence of overboring (and if so why)? and can anything be done to stop it - ie fitting lighter pistons.
(It's fully balanced and has got a pheonix crank, 30mm carb, reprofiled cam and ally head)

OH, I knew this would happen! Tell us more about the Carb, and type of distributor.

It's a solex MOV - 30mm updraught barrel throttle, with a fabricated inlet manifold. The distributor is standard Lucas; original to the engine(early'28)

I see "Doomy" has raised a couple of areas to consider.Well,Hum,The distributor? This has no centrifugal advance so perhaps this may effect the performance. I suggest trying a late distributor as a start. The carb I am not familiar with,but instinct tells me it may well be over carburated. I have done engines ,in the ,past built with 080 pistons and it is not been necessary to have such a big choked unit. Is it in fact a proven set up? Or is it experimental? Mac.

Tom,

I have a +80 block on Phoenix crank but still use a DJ4 distributor and a Zenith 26VA carb, I think your problem could well lie with the re-profiled cam as these can make the engine very 'lumpy', my engine is not 'fully balanced' although I did what I could to statically balance it but it runs very quietly ( for an A7 !! ) unless you are going at full bore. I can get 40 mph in 3rd gear ( and do regularly ). The car is an RK saloon.

One other thought, a lot of noise comes from chatter in the timing gears if they are slack, without load on the camshaft there should be no appreciable play between the two cogs although they should not be tight. Not only does any free movement in the gear cause noise it also allows the timing at the distributor to vary. I am using a new pair of gears from Vince Leek and I am sure they make my engine quiet.

Finally you cannot get more bang from an Austin Seven engine and expect not to hear it !

Malcolm - 40mph in 3rd gear in a RK, that's not fast, I think you have forgotten to mention you have a 4 speed box in the RK.

Re. timing gears noise, I'm surpprised how litle attention seems to be given to matching the gear size (to nearest 0.5 thou inch) to those marked on the crankcase, and is there a possibility that fitting lower marked offset worn gears will reduce the noice - e.g. if the crankcase is marked +1 1/2 and you fit +1, will these make less noise?

Naomi (back from holiday)

Hi Naomi, good holiday ?

You mention +1 1/2 marking and using a +1 but I think that is the wrong way round. If my information is correct, and please I will not be offended unlike others if I am corrected, when they made the engines they could not ensure accurate spacing of the crank and cam shafts so they bored the bearing housings and then measured them to find the error. This error was then stamped on the crankcase i.e. + 1 1/2. This meant that a + 1 1/2 oversize cog pair had to be fitted, again stamped with the error. With wear I would, therefore, suggest that a better fit MIGHT be achieved by using a +2, or larger set not a smaller set.

Am I right or wrong ?. Whatever set is used if there is play between these gears you will not have a quiet engine.

Malcolm

Malcolm

I have often wondered too, which way round the markings refer. Few people seem to know they are there. If it can be verified by one of our contributors the correct way the markings are that would be great. I've scoured the Grey Mags, but cannot find any reference to these marks and thus the fitting of the correct size gears for the crankcase marking. I am building an engine at present with multi-sourced parts and thus this info would help, especially if it results in a quite enging, OR if someone was to manufacture a non-metallic gear wheel for the end of the camshaft, that would help!

Sandy

Hi Malcolm, I had a lovely time, but missed my pink RN.

Your right, I'm sure, if original is + 1 1/2 thou, fit worn 2 thou. It's also important to make sure the camshaft end float is no more or less than 2 thou and the faces of the camshaft gears are in line for the correct timing.

Sandy say's he cannot find a reference in the Grey Books, well I couldn't find one in the 'Companion' either, but Woodrow's Manual does mention the 'tolerences', and that they are not marked on pattern gears. Woodrow further says if the engine was running OK (quite?) don't interfere.

Naomi

Page137 of companion is about meshing of timing gears,article from 1968. I thought I'd read it somewhere!
Regards Andy

.

There are a pair of gears on eBay as we speak, coming up midday Sunday.

4593826971

I have posted a question as to what figures might be stamped on them.



Mike

Sandy mentions the possibility of manufacturing non metallic timing gears...

Excuse me for using a swear word but the Ford V6 used a fibre timing wheel which was known to shear with disastrous consequences. Tuned engines were often fitted with steel timing gears which funnily enough are quoted as being noisy!

Steve.

p.s perhaps Malcolm could make some up in his workshop, after finishing the billet crank and home poured rods?

Missed 'Timing gears meshing' in the Companion, I don't know why, obviously brain had input wrong search data!!!!

HOWEVER, this seems to say the opposite of what Malcolm and I assumed, by the fact that a 'Standard' (e.g. 0 thou tolarance) gear in a crankcase marked + 1 1/2 thou, sheared a tooth from overmeshing, our consenus would have been that the meshing would be loose and noisy.

I too had in the back of my mind I had read and seen illustrated the item in the Companion, it's a question of finding the reference.

Naomi

Mike, there is only the timing location marks on the gears - thus pattern gears, there are no +/- or 'S' marks on them.

I asked Tony (Pearl_Opal) when they first came on ebay.

Naomi

.

As they used to say to me at school 'late again'!

Mike

Is a plus 1 1/2 thou still a plus 1 1/2 after it has been running for 40 or more years?

Ian, that's why I was suggesting putting in worn +2thou, on the basis that would compensate for the 1/2 thou wear on a 1 1/2 thou tolerence, at least I think that's what I was saying.

The problem is the Companion item where the crankcase is marked +1 1/2 thou and it was fitted with a standard (0 thou) gear and suffered.

We await the black hand gangs responces....

Naomi.

the camshaft is a pigsty fast road type - its got more overlap than standard but it isn;t very wild. The carburettor is the same kind fitted to unsupercharged ulsters - so it should work ok.
as for timing gears - what about bronze? our mag engined chummy had new gears 5000 miles ago, and they're worn and noisy allready...

Tom,

I have done 4000+ miles with Vince Leek's gears ( and I am not on commission! ) and they are as quiet as when they were put in. Vince uses two different types of steel in his as the crankshaft cog does twice as much work as the camshaft cog.

Talk to Vince about cogs.

Malcolm

Naomi,

My reading of the Companion, page 137 is that a +4 thou cog was used in a + 1 1/2 thou block, and back in the Sixties ( when less wear had taken place! ) and the suggestion is that they were too tight and broke a tooth.

This would seem to fit my understanding of the marks. ( Am I beginning to sound like 'Angry from Ongar' ? ).

Logic would have it that if the bores were too far apart compared with standard then the error is a + and the adjusted cogs would have to be bigger and marked +.

Having confused everyone I will now retire.

Malcolm

Reading the Companion, page 137, I found it confusing as ref 'D' is used on both the 'S' (0 thou) and +4thou illustrated cogs. Presumably A.K. George knew what he meant and thus did not have to clarify it in the article. Looking closly, I suppose one 'D' ('S') has split, the other 'D' (+4thou) has come off.

Overall I believe you are right Malcolm about the dims. I have too have used Vince's gears, no complaints, proper job.

Dennis O'Brien

Tom,
It would be interesting to know the compression ratio and what fuel you are using. I find it curious that it's rougher if you rev it. I would not have thought this would be so if the cam profile/timing were to blame, rather the opposite. Ignition timing presumably beyond reproach? No significant wear in distibutor or drive gears?
Honda pistons are pretty light already. Is the flywheel lightened? I am thinking of the balance between explosive forces and rotating masses.
Ferocious Maxi valve springs? Standard sized valves? Which ally head? Beginning to run out of ideas!

Regards, Stuart

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.

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

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.

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

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!

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

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.

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

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

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

Cedric