Technical 500L Dying when Warm

[criceo]

Hello all,

It's been a long time since I posted on here. My '72 500L is on the road again, sort of. It managed to drive it for thirty minutes for the first time in a year, but, like before, it just kept losing power as it got warmer, eventually dying just as I pulled into my driveway. Although, unlike last time I posted about this issue, it did eventually restart after I let it cool down for many hours. I tried replacing the 123 ignition with the old points since the coil was getting scalding hot to the touch, but I don't think it's made a difference.

It's the same story: it starts fine when cold and pulls fine at first. However, the engine slowly loses power to the point that the car cannot proceed and the engine eventually dies. I don't know what it could be. It looks like I have fine fuel flow through the transparent filter when hot. The engine isn't missing on one cylinder or the other. I'm not sure if the coil getting burning hot is a result of an ignition problem or it being in the direct path of the air coming off of the cylinders. On that note, the air flap is opening at high temps. The car idles fine, but 35mph is top speed with my foot hard to the floor in 4th. The plugs are very sooty, but that may be from repeated failed starts while setting the timing. I'm not sure what else to check at this point. Looking for advice.

After replacing the 123 with points, I now also have a generator warning light. I tested across the generator leads, the battery leads, and the battery terminals. The generator and battery leads have 0 volts across them. The battery has 11.5V across the terminals. I expected to read a voltage and amperage across the leads. The generator light did go out on the last test drive at high revs, but now it won't go out revving it in the driveway. I've had to run the car off another battery with jump leads, and as soon as I remove the leads the car begins to idle much faster. The belt does not appear to be slipping. Advice on this problem would also be appreciated.

 

[Goldnrust]

Have you tried changing the coil itself? It's not unheard of for damaged coils to work ok when cold and then stop working when they get hot?

If the plugs are very sooty, and the car run progressively worse as it gets hot, could the choke be stuck on?
Or you have another issue, such as a sunken float, that's causing the car to run really rich?

Another cause of poor hot running can be valve clearances that have closed up. The the engine gets hot the valve can then be held open causing a loss of compression.

Maybe it's worth getting the engine hot till it fails then checking for spark at the plugs and compression? Ultimately they are simple little engines and they need 3 things to run; fuel, compression and spark. So if you can check for spark and compression, then you can work out which of these 3 branches are the root of the problem and move forward with trouble shooting from there.

 

[Sbf500]

Have you tried changing the coil itself? It's not unheard of for damaged coils to work ok when cold and then stop working when they get hot?

If the plugs are very sooty, and the car run progressively worse as it gets hot, could the choke be stuck on?
Or you have another issue, such as a sunken float, that's causing the car to run really rich?

Another cause of poor hot running can be valve clearances that have closed up. The the engine gets hot the valve can then be held open causing a loss of compression.

Maybe it's worth getting the engine hot till it fails then checking for spark at the plugs and compression? Ultimately they are simple little engines and they need 3 things to run; fuel, compression and spark. So if you can check for spark and compression, then you can work out which of these 3 branches are the root of the problem and move forward with trouble shooting from there.

My coil went like this and it was infuriating, especially when another new coil went the same way. The main issue would be it would die when hot and then if I took out a plug and checked for a spark one would be there. On the face of it, all was fine, I had fuel, I had a spark, timing was fine, valve lash fine, and up until the point of it getting hot and starting to die it was, for a standard 498, pulling like a train.

Eventually I got to replacing every thing electrical, even retired the whole thing. Nope problem still there. Eventually I came across the original old red coil I had taken off the car probably around 15 years ago. Anyway popped it on and never had an issue since.

One thing I did do was when hot I checked the spark, oh my I nearly fell over. Basically the spark I had been seeing previously was really weak in comparison.

I think my new new coil failed in the same way, or at least didn’t like the heat, as the original new one did.

 

[criceo]

Alright, no promises since I couldn't go for a test drive due to the rain today, but I think the dying issue has been solved. A new coil seems to have been the solution. The old Klitz coil I took out was, from what I've read, standard issue on Fiats of the 70's; so, combined with the ancient state of the oil filter when I got this car, I wouldn't be surprised if the coil was decades old. After installing a Beru coil, it's idling much stronger and the exhaust smells so much better. No stink of unburned fuel. And the exhaust gas and coil are much cooler.

Now I have a dynamo issue. The charging light comes on at really low RPM; so, I've set the idle a little higher. High revs for a few seconds cause the light to go out and stay out until the revs get really low again. Then it stays on until I rev again. I used a multimeter at the battery terminals, and the leads are providing ~11 volts. I'll follow the procedure I found on this site for generator testing later this week. The belt feels nice and tight.

 

[the hobbler]

Alright, no promises since I couldn't go for a test drive due to the rain today, but I think the dying issue has been solved. A new coil seems to have been the solution. The old Klitz coil I took out was, from what I've read, standard issue on Fiats of the 70's; so, combined with the ancient state of the oil filter when I got this car, I wouldn't be surprised if the coil was decades old. After installing a Beru coil, it's idling much stronger and the exhaust smells so much better. No stink of unburned fuel. And the exhaust gas and coil are much cooler.

Now I have a dynamo issue. The charging light comes on at really low RPM; so, I've set the idle a little higher. High revs for a few seconds cause the light to go out and stay out until the revs get really low again. Then it stays on until I rev again. I used a multimeter at the battery terminals, and the leads are providing ~11 volts. I'll follow the procedure I found on this site for generator testing later this week. The belt feels nice and tight.

I will concede that it is many years since I drove a 500 with a dynamo (as against the engine in my car now which has an alternator--126 engine), but I seem to remember that the ignition light ALWAYS came on with a low idle speed, and then went out as the revs went above (about) 1,000rpm. Was this not the problem with dynamos (of all types)---not charging at low revs?

 

[fiat500]

Alright, no promises since I couldn't go for a test drive due to the rain today, but I think the dying issue has been solved. A new coil seems to have been the solution. The old Klitz coil I took out was, from what I've read, standard issue on Fiats of the 70's; so, combined with the ancient state of the oil filter when I got this car, I wouldn't be surprised if the coil was decades old. After installing a Beru coil, it's idling much stronger and the exhaust smells so much better. No stink of unburned fuel. And the exhaust gas and coil are much cooler.

Now I have a dynamo issue. The charging light comes on at really low RPM; so, I've set the idle a little higher. High revs for a few seconds cause the light to go out and stay out until the revs get really low again. Then it stays on until I rev again. I used a multimeter at the battery terminals, and the leads are providing ~11 volts. I'll follow the procedure I found on this site for generator testing later this week. The belt feels nice and tight.

The charging light will come on at low rpm with a dynamo; but 11 volts is too low when running at anything above fast idle. But other than that, the scenario you describe actually sounds normal. Even though I have fitted an alternator, there is still a point at which the charging cuts out or in at idle, and reverts to or from battery voltage.
I recommend that everyone should fit voltmeter so that you have a constant eye on the charging situation. I have one that was cheap,and simple to fit, and doubles as a USB outlet. I'm normally seeing 13+ volts when driving the car.

 

[criceo]

Well, we're still getting 11.5 volts and a sporadic charging light. This time during the test drive it wouldn't shut off no matter how high I revved. But, when I pulled into the driveway, it went out. Maybe I'll clean up the ground wire and bolt for the dynamo. The battery seems to be staying at 12.5V; so, I'm not too worried.

In the meantime, I don't think we've completely solved the issue of dying. It's pulling stronger, that's for sure. But, it's still not at previous strength. I found a new potential culprit though: blow-by.

I went to take out the dipstick with the engine idling, and it died as soon as I pulled out the stick. I thought I had knocked the distributor; so, I started the engine again with the stick out. It wanted to die after starting, but pulling on the throttle linkage helped it to idle better. I reinserted the stick and the pulled it out again. Sure enough, when I pulled out the dipstick the engine bogged down. Then I felt the huge amount of gas being pushed out of the dipstick hole. I'll get a compression tester and see what I'm getting on both cylinders, but perhaps such a large amount of blow-by could explain the lack of power.

At this rate, I'm leaning more and more towards doing a 650cc swap.

 

[Goldnrust]

Sorry to hear the issue is not completely fixed. A compression test seems a good idea, if nothing else to rule out any mechanical issues.

The dipstick sounds very strange... Possibly a red herring. The crank case should breath freely via the vent in the valve cover, which feeds those vented gasses back into the intake. Unless that breather it's blocked, pulling the dipstick should make zero difference to the pressure inside the crank case.

And if enough pressure built up in the crank case to counteract any leakage of combustion pressure, that would be well beyond the couple of PSI needed to pop the dip stick out of the case?

 

[criceo]

Well, a compression test shows ~55 psi in each cylinder. That may indeed explain a few things.

I don't think it's valve clearance, as I can feel the blow by coming from the oil dipstick hole.

 

[criceo]

However, tightening the dynamo ground seems to have fixed our charging issue.

 

[criceo]

If I remember correctly, when my mechanic rebuilt this engine a year ago, he had the cylinders bored out a bit, due to scoring caused by the overheating. I think perhaps the new pistons and rings may not be sized quite right. If it is determined that this is the case and new pistons/cylinders are sourced, could one fit larger cylinders and pistons from the 126? I assume that when Fiat increased engine displacement for the 126 that they did so with bigger bores rather than lengthened stroke; as such, I would think that, if the pattern for the studs is the same, that adding larger diameter cylinders and associated pistons would allow for some easy hp gains without needing to install a new crank or con-rods. Is this the case?

 

[Goldnrust]

Did you do the compression test with the engine warm and the throttle held wide open?

Before counting on the low compression reading being due to ring wear, put a teaspoon of oil into each spark plug hole and repeat the test. If the compression jumps up then worn rings is likely. If it doesn't, then low compression could be due to leakage at the valves.

A certain amount of blow by is normal, as is the fact that in a parallel twins breathe quite hard through the crank case. Both pistons move together, so that the crank case will draw in 500cc of air on every up stroke and expel 500cc of air on the downstroke.

Not trying to doubt your conclusion, but just trying to save you money before you go and buy parts that might not be the root of your issue.

In terms of increasing capacity, the standard 500c block will accept 540cc barrels and pistons as a drop in performance upgrade. You can fit 594cc and 650cc barrels and pistons but you need to have the crank case bored out to accept them.

It's been done many times though also most owners find it easier to fit a complete 126 engine instead.

 

[the hobbler]

Did you do the compression test with the engine warm and the throttle held wide open?

Before counting on the low compression reading being due to ring wear, put a teaspoon of oil into each spark plug hole and repeat the test. If the compression jumps up then worn rings is likely. If it doesn't, then low compression could be due to leakage at the valves.

A certain amount of blow by is normal, as is the fact that in a parallel twins breathe quite hard through the crank case. Both pistons move together, so that the crank case will draw in 500cc of air on every up stroke and expel 500cc of air on the downstroke.

Not trying to doubt your conclusion, but just trying to save you money before you go and buy parts that might not be the root of your issue.

In terms of increasing capacity, the standard 500c block will accept 540cc barrels and pistons as a drop in performance upgrade. You can fit 594cc and 650cc barrels and pistons but you need to have the crank case bored out to accept them.

It's been done many times though also most owners find it easier to fit a complete 126 engine instead.

Did you do the compression test with the engine warm and the throttle held wide open?

Before counting on the low compression reading being due to ring wear, put a teaspoon of oil into each spark plug hole and repeat the test. If the compression jumps up then worn rings is likely. If it doesn't, then low compression could be due to leakage at the valves.

A certain amount of blow by is normal, as is the fact that in a parallel twins breathe quite hard through the crank case. Both pistons move together, so that the crank case will draw in 500cc of air on every up stroke and expel 500cc of air on the downstroke.

Not trying to doubt your conclusion, but just trying to save you money before you go and buy parts that might not be the root of your issue.

In terms of increasing capacity, the standard 500c block will accept 540cc barrels and pistons as a drop in performance upgrade. You can fit 594cc and 650cc barrels and pistons but you need to have the crank case bored out to accept them.

It's been done many times though also most owners find it easier to fit a complete 126 engine instead.

As"goldenrust" has mentioned, the '540'conversion is very easy job---a case of old barrels and pistons out---new barrels and pistons in. It is of course an engine-out job---so you might as well fit a better cam (35/75/75/35) and the 28IMB carb (off a126) at the same time. The 500 (type 110) can take the fitment of 652cc barrels--but no more. There is are rings cast into the top of the crankcase at the perimeter-edges of the barrel apertures. These are for the barrels to sit on with a gasket (paper or copper, which I prefer) between the bottom of the barrel and the top of the rings. If the crankcase apertures are opened up more that is required for the '650' barrels, these rings dissappear, and then the complete top surface of the crakcase has to be machined flat and a spacer-plate put between the barrels and the top of the crankcase---it's a real faff working out how thick the spacer plate needs to be and then obtaining one, and more expense!
When fitting a '650' engine, the 500 gearbox can be retained (much the stronger of the gearboxes), but a '126' gearbox bell-housing and starter have to be fitted, along with the special dust shield, the starter brace-bracket and the special '3rd bolt' for the starter. If you 'just fit 650 barrelsand pistons' into the engine, the starter system stays the same, and the car is still a "matching numbers" car.

 

[criceo]

A hot compression test revealed the same psi as before. I tried to dribble a bit of oil into the cylinder and tested again. The psi was about the same, if a little lower. However, that lower psi could be attributed to the fact that I had left the oil dipstick out for the latter test. Either way, no change. I have to get a new tester, as this cheap piece of crap from Amazon broke at the end of the tests today. Perhaps it's been giving me false readings?

I thought the dynamo issue was solved, but clearly not. I took the car for the first highway test yesterday. I had the headlights, speedo light, and radio (a useful addition), on. I thought it was charging ok, because the charge light wasn't on and I had read 12.something volts at the battery leads. I now realize that the charge light didn't even come on when I turned the key with the engine not running and that the 12v was just from the freshly topped up battery.

As for said test drive, it just confused me more. As usual recently, the cold start required a minute of light throttle to keep the car from dying. It drove fine to the parkway, got up to ~59mph, old top speed, slowly but surely, and was fine when I got off the parkway for a minute to turn around. It maintained a cruising speed of ~55mph no problem until I got to my exit. Then, when I got off onto my exit ramp, it became anemic. ~15mph in 3rd was all the car could muster. The engine was hardly turning over. Even in neutral, it sounded awful and extremely weak. It did manage to get me home, dying in front of my house, where I read ~9volts at the battery. I jumped the car with another battery, but it wouldn't fire. I got it back inside later, and it ran today for the new compression test.

So, combined with the new compression test, I still don't know if the only problem left is a charging one or also a compression issue. Did the car die only due to no charge? If it is a compression problem, one would expect it to not be able to maintain top speed, as well as accelerate to that speed from a stop during the middle of the test. If it was only a charge issue, why wouldn't it hot start with a new battery? I'm going to order a new voltage regulator and keep the old one around, probably going through it another time. I may order new pistons and jugs at the same time in order to save on shipping.

 

[criceo]

Ok. New regulator in place. I don't think things are fixed, but we will see. In the meantime, I think I've found another potential source of low compression. I saw smoke puttering out near the starter when I revved the engine from idle. It seemed to put less at idle and as revs increased. Small revving produced the most smoke. Perhaps a bad gasket.