I've been reading the old posts on oil pressure but still have questions. I have a 1970 500L with a 'good' used engine (dealer's terms). When I received the car, the thermostat was stuck closed and the oil pressure light would come on after 10 minutes. New thermostat now and I still have the oil pressure light problem. I replaced the sender with a mechanical gauge and see I have 52psi cold, 6psi hot and 0psi when driving. I now have the oil pump out as the easiest solution to try first is to replace it. From visual inspection, it looks perfectly fine. No sludge in the oil slinger, passages look clean, pump looks good. I can't really tell how worn the gears are but they appear OK. Could my problem be the oil pressure relief valve? Is this the spring built in to the pump itself? Is there a quick test for that?

MrFiat has new oil pumps for a 500R/126 with a note they need modifying to fit a 110F. What modification? Should I just buy a 126 timing cover and oil pump? Where can I get one complete, preferably in the US? Would it still need modification? I like the idea of a larger oil pump but want someone to say it will work and how!

Hi Marcus,
Low oil pressure is not unusual on a 500 and is rarely caused by the oil pump.
It is worth checking the oil viscosity- if the oil is too thin the light will come on- I use a 10W60 synthetic that works well even in very hot weather (40 degrees +)
Most common causes are the sealing plugs in the centre of the crankshaft- there are two metal plugs that can come adrift and cause low oil pressure and consequent bearing damage if left unattended.
You can check by removing the sump and inspecting these plugs- you can tap them back in with a hammer and peen the edges with a punch.
Also check that the oil pickup is not blocked with sludge or leaking where it bolts into the crankcase- there should be a large flat rubber washer to seal it.
Otherwise the other places to look are the sealing surface on the face of the oil pump to the camshaft which look good from the pictures.
Another common area of pressure loss is the front camshaft bearing- this runs in the crankcase so it is an engine apart job to machine and replace with a bearing insert- in some cases it can be easier to look for a replacement crankcase or engine.
Finally there could be excessive clearance in the main bearings- I recently discovered someone had fitted a standard main bearing to a reground (undersize) crank- replacing it made a vast improvement!
Good luck and feel free to ask if you need more help!

If you have 52psi on start up the pump can't be that bad. If a crankshaft plug shifts or drops out then you will never get any oil pressure, hot or cold. I have an engine that had that happen and the seller had masked the fact by disabling the oil light & switch. By the time I found out the crankshaft bearings were worn but fortunately not to the extent that the crank needed grinding so new bearings and a replacement core plug solved the problem. I also use 10w/60 like Damon & it ticks all the boxes for me. You could try dropping the sump and look for any other signs and it might be worth trying a new set of big end shells as a cheap quick fix otherwise it will mean engine out for new mains. I did notice from your picture that you have a rather slack Fiat 126Bis timing chain in there as there are no tensioners on the links unless it has been fitted back to front which would cause a whole new load of problems.
Did the dealer mean by "good used" that he slung together a load of bits that sort of work?

I'm running Brad Penn 20W50 for oil. Dealer asked me to try Oil Stabilizer, so I replaced 1/2 qt with this. Same 52psi cold but now I have oil spewing out of the crank pulley seal. That is why I pulled the cover and plan on upgrading to a 126 cover and oil pump. If that isn't my problem, sounds like bearings. What should the timing chain look like? The slack on top looked bad to me, but I don't know what is normal on these. How can you tell it is a bis chain?

I have the Haynes manual on order. Hopefully it will make me smarter

Mark


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marcus550 said:

What should the timing chain look like? The slack on top looked bad to me, but I don't know what is normal on these.

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Hi Mark,

The attached photo is a close up shot to show the timing marks but you can also see enough of the timing chain to help with your question. The chain should be tight and in the photo you can see the tensioners on the links.

Chris

morning mark;
I would suggest that you do heave the engine out and give it a full inspection. Check that the oil supply holes in the main bearings are correctly aligned with their matching holes in the crank-case. A friend of mine has run into this problem with a almost identical scenario to the one you have--plenty of initial oil pressure, then pressure fall-off. It sounds as if your engine supplier has just chucked it together with not a lot of care or attention to detail---all the best, let us know what the eventual outcome is please

I have the front crank shaft bearing off now. How can that bearing be installed incorrectly? Regardless, the crank is obviously wrecked with noticeable grooves running around it. The bearing has rough spots on it as well. So, I'm taking the engine out this weekend to pull the crank shaft. Ugh.

I did purchase a used Fiat 126 front timing chain cover and new 126 oil pump. I'm having trouble with that as well. When the pump is out of the cover, the gears mesh and turn smoothly. When I bolt it in to the cover, it spins freely almost 360 degrees and then sticks HARD. I can't spin it past this sticking point without using a tool on the shaft for leverage. I'll dye it to see where the interference is but geez, how many problems can I have?

New Fiat 126 Oil pump update: The driven pump gear was out of round! I dyed the parts and assembled it, spun it around, and took it apart. 1/4 of the teeth on the driven gear were shiny on the ends and the others remained blue. I then had our inspection dept. measure it. The gear appears to be out of round, the center hole was .005" off center. This caused the gear to bind against the timing cover on the high side. Everything else measured fine; shaft was straight, gear was pressed on flat. To fix it, we ground the teeth on the high side to match. It spins freely now when assembled. It might be slightly less efficient? But the 126 pump is much larger than the stock 500 pump so I'm guessing it should be OK.

So, the saga continues. New crankshaft, new main bearings, new rod bearings, new (correct) timing chain and pulley set. New 126 oil pump and used cover. New gasket set. Filled it with oil and cranked about a minute before oil pressure started coming up. Fired it up and let it idle. Got a good 60psi of oil pressure on the test gauge. Let it idle for 10 minutes and this settled down to 10psi. Great! I pulled the gauge off and put the oil pressure light sending unit back in. Took it for a ride and only got about 10 miles before the oil pressure light came on.

The following week I pulled the rocker assembly out and inspected that. Looks good to me. Cleaned it up and greased it, put it back in, had to replace the adjusters. Re-tightened the head bolts as specified. Set the valves and put it back together. Installed the oil pressure test gauge again and took it for a ride. 60psi cold, 10psi warm, but after only a few miles, 0psi while driving. If I rev the engine out of gear, it only crept up to 4-5psi.

So, from the above comments, the only thing I can guess is that front cam bearing (the case itself.) Not easy to get a 110F case. I only see then in Italian on-line shops. I guess I could machine the opening and press a bushing in there? Might as well do both ends while I've got the case out. Geez. What a pain! Anyone done this?

One of my crankcases is damaged at the front camshaft bearing surface so I took a chance and bought a repair bush from the German Axel Gerstal shop. I say took a chance because the item description seems to have gone wrong in the translation but it is a plain bush that is designed to be a press fit into a bored out case.

Hi, Toshi

Have you installed that cam bushing yet? Is it for the pulley-end or the flywheel-end of the camshaft? It says 'steering-wheel-sided' on their site. Not sure what that means!

How did you know yours was worn out?

Not fitted yet as I will need to go to a machine shop at some stage. Yes it does go at the drive end of the camshaft . The steering wheel bit threw me which is what I meant by taking a chance. There is nothing special about it and you might be able to get something suitable made up closer to home.

marcus550 said:

New Fiat 126 Oil pump update: The driven pump gear was out of round! I dyed the parts and assembled it, spun it around, and took it apart. 1/4 of the teeth on the driven gear were shiny on the ends and the others remained blue. I then had our inspection dept. measure it. The gear appears to be out of round, the center hole was .005" off center. This caused the gear to bind against the timing cover on the high side. Everything else measured fine; shaft was straight, gear was pressed on flat. To fix it, we ground the teeth on the high side to match. It spins freely now when assembled. It might be slightly less efficient? But the 126 pump is much larger than the stock 500 pump so I'm guessing it should be OK.

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What did you grind the gears with. I think I have the same problem. I have tried filing the teeth but it seems to still be just catching on each revolution.

Cheers. Geoff

Our machine shop has a grinder just for small gears like this. I imagine the gear is hardened so just filing it could take a long, long time.

Thanks

It did take a long time to file but on measuring, did not need too much.

It is spinning freely now so all good.

It was very helpful to have your original post as a reference.

Cheers

Geoff

marcus550 said:

So, the saga continues. New crankshaft, new main bearings, new rod bearings, new (correct) timing chain and pulley set. New 126 oil pump and used cover. New gasket set. Filled it with oil and cranked about a minute before oil pressure started coming up. Fired it up and let it idle. Got a good 60psi of oil pressure on the test gauge. Let it idle for 10 minutes and this settled down to 10psi. Great! I pulled the gauge off and put the oil pressure light sending unit back in. Took it for a ride and only got about 10 miles before the oil pressure light came on.

The following week I pulled the rocker assembly out and inspected that. Looks good to me. Cleaned it up and greased it, put it back in, had to replace the adjusters. Re-tightened the head bolts as specified. Set the valves and put it back together. Installed the oil pressure test gauge again and took it for a ride. 60psi cold, 10psi warm, but after only a few miles, 0psi while driving. If I rev the engine out of gear, it only crept up to 4-5psi.

So, from the above comments, the only thing I can guess is that front cam bearing (the case itself.) Not easy to get a 110F case. I only see then in Italian on-line shops. I guess I could machine the opening and press a bushing in there? Might as well do both ends while I've got the case out. Geez. What a pain! Anyone done this?

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I had a engine in a few years back, no oil pressure but heavy revs would improve things....engine had been rebuilt, rings/bearings etc., the problem I found after a lot of head scratching was the rings in the front main bearing had been put in the wrong way round....

How many of the people with oil pressure problems (when engine hot) have built their engine around a modified 500 crank-case (as against a 126 crank-case)? I was spending some time with agent who builds and tunes a LOT of 500/126 engines the other day and he was pointing out to me the various differences between the 500 engine variants and the 126 engines. The 126 timing-chain cover is deeper than the 500 timing-chain cover, and the oil-pump is slightly longer. There is reason to believe that if a 126 oil-pump is fitted into a 500 timing-chain cover (which it will) the extra length of the oil pump could mean that the relief valve in the oil-pump is being held slightly open all the time---hence oil-pressure when engine cold (and oil thick) and very little oil-pressure when engine hot (oil thin and aluminium components expanded). If you are 1 of the people suffering this oil pressure loss problem, and you are using a 500 crank-case based engine, you MUST use a 500 oil-pressure pump---it will still produce plenty enough oil-pressure.

I'm using the old 500 housing and pressure relief with new gears so should be ok. Thanks for the heads up though. This will be useful info for people in the future.

I assume the aluminium housing expand more than the gears. I have them spinning freely when cold but don't want it to start machining aluminium when hot....

the hobbler said:

The 126 timing-chain cover is deeper than the 500 timing-chain cover, and the oil-pump is slightly longer. There is reason to believe that if a 126 oil-pump is fitted into a 500 timing-chain cover (which it will) the extra length of the oil pump could mean that the relief valve in the oil-pump is being held slightly open all the time---hence oil-pressure when engine cold (and oil thick) and very little oil-pressure when engine hot (oil thin and aluminium components expanded). If you are 1 of the people suffering this oil pressure loss problem, and you are using a 500 crank-case based engine, you MUST use a 500 oil-pressure pump---it will still produce plenty enough oil-pressure.

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Tom I have to pick you up on one point there. You say that the 126 oil pump gears will fit into a 500 cover. Well it will not simply because the gear thickness or oil pump depths are so different. 10mms on the 500 & 14mms on the 126 so quite a difference. The only issue I have encountered in compatibility of parts was when the dog drive on the oil pump would not fit into an original NOS 500 camshaft so that might be something to look out for.

Yes Toshi, I am aware that the thickness of the 126 oil-pump gears is greater than those of the 500; what I was trying to say (obviously not very successfully) was that a complete 126 oil pump unit will bolt into the 500 timing-chain cover, and if you are not aware of the difference in depth of the 126 pump over that of the 500, you could end up with a pump with the relief valve being held open slightly all the time, and thus causing a lack of oil-pressure when the engine is warmed up---but thank you for highlighting the difference in gear thicknesses, I didn't know the precise difference.