Hi,
My engine (original 499cc) is running better now that some loose electrics were discovered and the fuelling adjusted using a CO meter (idles at 1000rpm with exhaust CO of 3.5 is that ok?)
Compression measures at 80 in cylinder 1 and 90 in 2 but only on the final 5th or 6th turn. Is this acceptable or is it enough reason to inspect the valve seats - any opinions? We couldn't find exact information but my friend said he'd want 120 psi on a 4 cylinder mgb engine, presumably it would be less here though.
Thanks for any advice in advance,
David

I'd set the tappets and retest- those readings should / could improve

First off I would say your compression is low. Also, the difference between the cylinders is too high. The difference should not be more than 10% maximum. My 1969 499cc well used engine in my car shows 95psi (6.6 bars) and I think that is a little low.
So just to make sure, you ran the compression test with both plugs out and the throttle held wide open?
Cam timing has an affect on compression tests. These cars don't have real aggressive timing, but you should check to make sure the timing is correct and that the chain is not slack, and the valve clearances adjusted correctly.
You should put a little oil in each cylinder and run the compression test again. If the pressure comes up, then you have worn rings / cylinders. If not, then the head gasket, intake and exhaust valves are suspect.
Here is how to check the valves. Take the valve cover and the air inlet to the carburetor off. Make sure a cylinder has both valves completely closed. Use an air gun with a rubber tip to seal against the spark plug hole tightly. Pressurize the cylinder with 90psi and listen for air leakage. If the leaking air sound comes from the exhaust, then the exhaust valves are leaking, if it comes out the carburetor then the intake valve is leaking. Repeat for the other cylinder.
It is also quite possible, and maybe most likely, that you need a new head gasket. If the engine passes the oil in the cylinder test for worn rings, I think if it was my car I would pull the cylinder head and replace the head gasket, inspect the valves to make sure they are sealing and at the very minimum lap the valves to their seats.
You can check the valves for sealing after you remove the head by turning the head upside down and pouring gasoline into each combustion chamber. If the gasoline leaks out you have found at least one problem to solve.
John

I agree with the above posters' advice.

Remember that compression ratio will have an effect on compression pressure. So e.g. if your C.R. is 7:1. then compression pressure will be a maximum of 7 times atmospheric pressure. 7 x 14.7 = 103 psi.

If your C.R. was 9.5:1 then compression pressure would be a max. of 140 psi.

Both 80 and 90 psi seem too low to me, I'd like to see 100+ psi on a standard (stock) 500.

Al.

Many thanks for the advice.
This test was done with the starter motor only and one plug at a time. I recently checked the tap pets. I think I would like to see what the valves and seats are looking like but would hope not to strip the engine further. I'll have to read up about compression ratio! David

Very well said from gentlemen above. 80sounds low to me also even with only plug out at a time you should have more than this. My opinion for everyone that decide to remove the head is to also remove the cylinders and inspect/clean piston rings, even with a new set of rings if old are worn engine will run much better for so little effort. I was about to do that but I decided to go for a 650 motor.
Thomas

Thomas....save your money. Rebuild your 500 engine with a rebore and new pistons if needed. I did that three years ago and over 13,000 miles and I love the engine so much that I am now changing my mind about fitting a good 650 which is sitting here ready to fit.

Peter i found this little engine very nice but maybe not suitable for modern roads. Very slow acceleration and what about hills with four passengers inside, wife and two little kids. I was told from other owners that a 650 is much better and can take hills with ease. I want to be able and drive at high way at constant speed of 80 km/h with no problem. Be able to drive to work couple of times per week which is 70km in total and do it easy. Do you think a 500 can do that? Wouldn't be better to change it? Of course the money I will spend to buy the engine are probably more than the money I need to rebuild mine. This is an issue that concerns me now.

Thomas

gordinir8 said:

Peter i found this little engine very nice but maybe not suitable for modern roads. Very slow acceleration and what about hills with four passengers inside, wife and two little kids. I was told from other owners that a 650 is much better and can take hills with ease. I want to be able and drive at high way at constant speed of 80 km/h with no problem. Be able to drive to work couple of times per week which is 70km in total and do it easy. Do you think a 500 can do that? Wouldn't be better to change it? Of course the money I will spend to buy the engine are probably more than the money I need to rebuild mine. This is an issue that concerns me now.

Thomas

Click to expand...

I've always preferred to work with what I've got. With my luck, any time I've bought a secondhand engine or gearbox to rebuild as an upgrade,it's typically been in worse condition than my original.

Could you perhaps try out a 500 fitted with a 650 engine and see if it's really that much better on hills etc.?

Afaik the 650 engine was introduced on the 126 which is possibly a heavier car so the power to weight ratio on the 126 is probably the same (more or less) as on the 500 with a good 500 engine. Remember the 500 was introduced to provide low-cost transport for Italian families.....and they've got lots of hills in Italy....

Maybe, as Peter has suggested, a rebore/new pistons would suffice. Plus you could do a little work on the valves/ports/head/raise the compression ratio a little/ less restrictice exhaust if you wish etc.

There's also the question of originality. I just feel that in time, an original spec. car will be more sought after and more valuable. I'm not a stickler for originality myself but buyers of classic cars often are....

Al.

There is a guy close to me that has fitted a 650 engine, I will ask him for a ride and see how it is. If i get so much impressed then I might do it. As for originality this is an issue and that is why I will keep the old engine. Besides having a spare engine is always good.

Whilst I agree with all the other lads that 80psi and 90psi are low, what I would be very tempted to do, especially if the car has stood for some time is what I believe is called 'an Italian engine tune'. Set everything correctly (timing, tappets, mixture) and then give it a good hard drive. When you have done that remove BOTH plugs and re-do the compression test. It would be interesting to hear what the compression pressures are then. I realise that this is 'bush mechanics', but sometimes the simple answers are the best. I would also suggest that 1,000rpm is a bit high as an idle speed---800 to 850 might be more sensible.

What I would like to know is the top speed of this car with such a low compression engine. Its always good to gather information for future tbs.

gordinir8 said:

What I would like to know is the top speed of this car with such a low compression engine. Its always good to gather information for future tbs.

Click to expand...

I can't imagine the compression ratio would make a huge difference on a level road. The 500 has a modest frontal area and the aerodynamics cant be terrible or it wouldn't be able to do what it can with 17-18bhp so even if it were down by a couple of bhp it would probably run out to close to the same rpm giving a similar top speed. Of course on hills there might be more effect

I know I've veered this off-topic but Thomas, you make a good point about whether a 500 will meet your needs
What you describe will challenge it. I use mine almost entirely for solo driving and even one passenger affects performance. But tomorrow I will be driving the most severe road in the UK to 800 metres and hairpin bends with over 200 Kms total driving. So a 650 will be better but 500cc is adequate for me.

Peter i love GB and i have visit it many times,your country is very beautiful... but flat. If Greece was that flat I wouldn't mind for a good 500 also.
Now let's don't spoil anymore our friends low compression case and see how we can help him.

As I'm a "weekend warrior" , I'll resume the battle with the engine then. I will try some energetic forward motion most likely in small circles in case I get stranded, I've actually not managed any journey more than 5 miles without a prolonged conk out since I bought it. Like many I've considered the 650 engine but I think my 500 engine is resurrect able without spending too much on it and it's a learning experience to figure out the seemingly myriad ways in which it can not run well.
Thanks, David

the hobbler said:

Whilst I agree with all the other lads that 80psi and 90psi are low, what I would be very tempted to do, especially if the car has stood for some time is what I believe is called 'an Italian engine tune'. Set everything correctly (timing, tappets, mixture) and then give it a good hard drive. When you have done that remove BOTH plugs and re-do the compression test. It would be interesting to hear what the compression pressures are then. I realise that this is 'bush mechanics', but sometimes the simple answers are the best. I would also suggest that 1,000rpm is a bit high as an idle speed---800 to 850 might be more sensible.

Click to expand...

^^^ x2. Some people refer to this as 'blowing out the cobwebs'

There was another version of the Italian Engine Tune-Up - It involved getting the engine warmed up and then dribbling water in through the carb opening while running the engine at a fast speed, circa 3000 rpm. This was supposed to clear out carbon build up in the combustion chamber and valve heads. I think it was a type of 'thermal shock'. Ever noticed how clean a cylinder/combustion chamber and valve heads are if there a coolant leak into a cylinder due to e.g. a leaking head gasket?

The Americans use a product called 'Sea Foam'? which they feed into the engine often through the brake servo vacuum hose. On a 500 I suppose you could dribble some into the carb opening with the engine running at a very fast idle. This stuff is supposed to dissolve gunk inside the engine incl. gummed-up piston rings? Reminds me of the old 'upper-cylinder-lubricant', Redex for example. Iirc, they also use some Sea Foam in the engine oil to clean out the internals before an oil change on neglected/laid-up engines. A bit like using a flushing oil treatment.

I'm not suggesting anyone try any of the above. There's a risk of causing damage. I've always been in favour of stripping an engine if there's an internal problem and fixing it properly, not using 'magic potions' or tricks seen on the internet.

Al.

REDEX---now there's a name that brings back memories! When I was but a callow youth, my father (a sergeant in the Met. police) initially ran old cars--it was all he could afford---Sunbeam, Lanchester and Lagonda (M45 saloon, which he used to rally as well in!) When he filled up with fuel, in the days of pump attendants, it was always so many gallons and the same number of 'shots' (squirts of Redex), and the 'shots' were 1p each. The only problem with Redex, (which was sold as an 'Upper cylinder lubricant) was that if you used it for too long it actually gummed everything up--not quite what one was trying to achieve.
As a 'first move', I still thank David should get all the settings and adjustments correct, cleanout the carb, fresh fuel and oil and then give the car a good blast, and if he can find a bit of a straight where he can 'put the pedal to the metal' so much the better. The chances of doing any damage to the engine are slim. but these little engines like to BE USED. When he has done that, remove both plugs and recheck the compressions. I think that there is a good chance that the compressions will come up, and the engine run sweeter---and it won't have cost him anything!