Technical 594 Engine Rebuild

[the hobbler]

Pertinent words of wisdom and advice Al. One of the reasons that I use "Westfield fasteners" for most of my nut and bolt requirements is that they list the relevant specifications of all the bolts that they supply. For example:--- a high tensile steel 8mm screw (full length thread) can be to:--ISO 4017 (DIN 933) in BZP (bright zinc plated), class 10 (10.9). Just for information they will supply a pack containing 10 of 8mm x 25mm to the above specifications for £3.15p + VAT.
Al is correct in pointing out that 'stainless' should NOT be used in any stress applications; I only use them for stress-less appearance reasons (holding the fan-shroud parts together/on etc.) Westfield can supply just about all the stainless/high-tensile bolts one would require, including plain and nylok nuts. They can even supply '1/2' nuts, both plain and nylok, for the occasion that a shallower nut is required----all at very sensible prices with first-class service. And that is the reason that I use the Company and recommend them.

 

[fiat500]

No worries regarding stainless steel; I can guarantee that there will be nothing shiny will be getting anywhere near this engine.

On that subject...to remove the shine from inside the barrels, I've invested in a honing tool. Before now I've always used a bit of well-oiled wet and dry paper. But for this purpose it really should be called "hit and miss" paper when you compare the results.

The cylinders do have a few light, vertical scores, which is not ideal. The lightest of these soon came out with a couple of minutes' honing. It might take too much off if I persisted to eradicate them all so I think I've stopped at the optimum.

It's simple to achieve and the only slightly dodgy part is avoiding getting caught up where there is that big cut-out at the bottom wall of the barrel.
I think that nice matt grey will provide the perfect key for the new piston-rings.

 

[fiat500]

With the pistons/barrels, timing-chain and gears installed, I'm now ready to fit the cylinder-head. My own head is in conflict over this; as the Fiat head is brand new, this would be a good time to have "bulletproof" valve-seats fitted. But it doesn't seem likely that I'll be able to have them machined at any point within the next six months. I want to get this job tidied up whilst I have the time, so I'll probably be fitting the valve-springs and fitting the head without having the head work done.

Still, it won't be a bad thing to have a new head, valves and springs fitted to this engine.

 

[F123C]

Hi Peter,

I wouldn't have the slightest hesitation in using that new cylinder head without fitting extra hard valve seats - I reckon the standard Fiat valve seats are hard enough.

Regards,

Al.

 

[Toshi 975]

Hi Peter,

I wouldn't have the slightest hesitation in using that new cylinder head without fitting extra hard valve seats - I reckon the standard Fiat valve seats are hard enough.

Regards,

Al.

I have to agree with Al here. Whilst I have come across some stunningly burnt out exhaust valves I have yet to see any real signs of valve seat regression due to modern fuels. It has been an ongoing debate for about 30 years or so and one guy in Australia stated that he had driven his 500 hard for over 100,000 miles and no head problems.

 

[F123C]

Hi Dave,

They're ^^ 2 beautiful examples of burnt out valves. I've always thought it strange the way they fail, looks like somebody nipped a little bit out of them.

Iirc, this advice that one must fit hard valve seat inserts started because some engines which had cast iron cyl. heads e.g. many Fords of the time, tended to suffer badly from valve seat recession when lead disappeared from petrol.
Often, these iron heads had the valve seats cut directly in the iron, so not very hard, they survived because the lead in the petrol supposedly provided a cushioning effect to the valve hitting the seat under the action of the valve spring - no lead = no cushioning effect, resulting in seat recession.

Regards, Al.

 

[fiat500]

. I've always thought it strange the way they fail, looks like somebody nipped a little bit out of them.

..and here's another from my original 499cc engine as found.

I was undecided about what to do about the intake-valve-stem "O"-rings on the 594 head...I was going to dispense with them seeing as they weren't in the engine gasket kit. But after reading back on previous conversations that I participated in on this forum I decided I'd better get some.

It turns out that the early Mini had the same sort of seal and the same valve-stem diameter, so bingo! you can get a set of 8 from eBay for £1.30. So now I have enough for another three engines after this one.

 

[the hobbler]

Looking at your '499' cylinder head Peter (and trying to ignore the valve) the combustion chambers look exactly how mine did---pitted. I am reliably informed that is caused by the ethanol in modern fuel. Even when using the Tesco 98 octain fuel, an 'anti-ethanol' additive is still required.

 

[fiat500]

Looking at your '499' cylinder head Peter (and trying to ignore the valve) the combustion chambers look exactly how mine did---pitted. I am reliably informed that is caused by the ethanol in modern fuel. Even when using the Tesco 98 octain fuel, an 'anti-ethanol' additive is still required.

I should have explained that this image was taken in 2013 and that the head did actually clean up very well. The engine can't ever have been used with unleaded as it was off the road long before leaded petrol was discontinued.

That's not to say that I disagree that unleaded petrol can do damage. I have read and I think I understand the explanations as to how how it absorbs water and that this comes out of solution and pools in carburettor bowls and the bottoms of tanks etc., but I'm puzzled that it might be a serious threat to a combustion chamber.

It's possible that native, micro-pitting of aluminium is mistaken for damage from other causes. The attached close-up of the combustion-chamber of my unused head shows a very roughly pimpled surface which I take to be the impressions of the casting sand.

 

[fiat500]

I did some reading-up on fitting these valve-stem "O"-rings and I think I might have done it wrong in the past. All the instructions I can find, which are for different cars from the Fiat 500/126, indicate that they are placed directly below the valve-collets and get trapped by the retainer-cup. Previously I've slid them over the valve stem just above the end of the valve-guide.

I see the sense in effectively sealing the retainer cup because that makes it into an "umbrella" deflector which impedes the oil which will be dripping down from the rocker-arm above. It's quite a fiddly job made harder because those tiny "O"-rings need a fair old stretch to make them fit over the valve-stem.

So now I'm ready to fit the cylinder head and move on to the next stage. I'll soon be out of the toy-room.

 

[Toshi 975]

Good to see that we have the same ideas about workshop essentials but I prefer the pizza sauce on the bearings as it is not so sticky

 

[the hobbler]

After reading your comments as to where valve-seals are fitted (on the valve), I looked up a number of BMC sites (the Classic car garage where I work, when I am allowed to, specialises in MG and Austin Healey) and they ALL say that the seal sits on the valve stem just above the valve guide. As the valve goes up and down, it will find its own position on the valve stem.

 

[fiat500]

Good to see that we have the same ideas about workshop essentials but I prefer the pizza sauce on the bearings as it is not so sticky

..good old Teksta...almost indestructible, just like these engines. I've never had a Hamm to help me, perhaps that's because I never have enough money left over from messing with cars to make it worthwhile.

I think you'll find that as it warms up, honey is a perfect running-in lubricant; but take note, it must be the squeezy kind or it doesn't work.

 

[fiat500]

After reading your comments as to where valve-seals are fitted (on the valve), I looked up a number of BMC sites (the Classic car garage where I work, when I am allowed to, specialises in MG and Austin Healey) and they ALL say that the seal sits on the valve stem just above the valve guide. As the valve goes up and down, it will find its own position on the valve stem.

Whilst I won't argue with an official workshop manual for a specific marque, it's interesting that you quote MG. It was when I followed a link, out of pure interest, which was to one man's very detailed account of the rebuild of an XPAG engine, that I became hooked on the idea that this might be a correct way to fit those rings.

The man, a Neil Cairns, gives a very convincing and almost overly detailed explanation of his every move. His thoughts carry some weight particularly since, as he says, he comes from an aeronatical engineering background. The "O"-ring is a part of a design intended to reduce the amount of splashed oil running down the valve-stem; it's unlike the positive seals as fitted to later Fiat and more modern cylinder heads.

If, as you say, and as I have done previously, you fit it loosely to the main part of the valve-stem, it will be pushed upwards as the valve opens and will always stay at that height. It will only make contact with the top of the valve-guide and make a momentary seal when the valve is at maximum opening. At all other points it is merely a passenger on the valve-stem.

If you fit the ring as I have done so that it is a fixed seal on the base of the collet-retainer, the oil dripping from the rocker-arm is completely deflected by the now sealed, collet retaining cup from running down the valve.

Of course, this is a pretty crude device in itself and doesn't prevent oil and vapour from being drawn down the valve-guide, particularly when the valves and guides are worn. The only real way to sort that out, (apart from fitting new valves and guides), is to fit modern, positive, sprung valve-guide seals for which (as you know from experience), can only be fitted on certain types of later head or ones which have been specially fitted with the correct, step-grooved valve-guides.

Obviously, the Fiat 500 engine is different in some ways from many other engines but the Laws of Physics with respect to flowing liquids remain the same. This is why I was so bold as to transfer the concept to my engine. No-one need follow my advice and I welcome any practical explanation as to why ALL the manuals you have read instruct that the rings be fitted as you describe. But in any case, right or wrong, I doubt it makes much difference anyway.

 

[Toshi 975]

I think you'll find that as it warms up, honey,it must be the squeezy kind or it doesn't work.

Bit like my wife by the sound of it but she asked me to cut her hair this morning now she is not speaking to me. I thought grade 2 would be fine
Anyway saved loads of money there plus that fringe benefit.

 

[fiat500]

I thought grade 2 would be fine

..well at least she won't need it trimming for a while now...have you done her eyebrows yet....simple job these days if she follows the trends, just shave them all off and paint them back on fairly high up her forehead.

 

[fiat500]

...a bit more controversy...or is it contra-versy?

I've torqued the head down now. It takes some tightening. I nipped up the nuts about one flat at a time in the correct order.....it must have been twenty times before I felt I was getting anywhere near the correct tightness. I even went back to the shed and tested the wrench in my vice for certainty! Then suddenly, one by one, another half turn and we were there....29 foot pounds...it's quite tight! I think it was a more decisive torqueing than I've done previously because I achieved it with perfectly dry nuts and studs. In the past I've been a believer in having the threads really well lubricated.

The tightness put me in mind of a recent posting where someone was worried they might crack the head because of the compression at the pushrod tubes reacting upwards. I think that there's no chance of that happening but it's obvious that the THICK seals supplied for this engine get really well compressed by all this. You can see my belt-and-braces approach with the thin wipe of sealant I've used to supplement the leak-proofing on these notorious seals. I'll be going round it with a fine blade to remove the surplus. You may see that I have aligned all of the tubes to ensure that both of the slots on each of them has access to the surplus oil pooling on the surface of the head. I have not previously considered this and let them sit randomly. This can lead to them not having both slots facing the pooling area which maybe reduces the oil flowing down to the cam-followers.

The next job is to strip and examine the rocker-shaft.

 

[Bleeding Knuckles]

.. You can see my belt-and-braces approach with the thin wipe of sealant I've used to supplement the leak-proofing on these notorious seals. I'll be going round it with a fine blade to remove the surplus. You may see that I have aligned all of the tubes to ensure that both of the slots on each of them has access to the surplus oil pooling on the surface of the head.

Looks like the build is coming along well Peter, like you I have resorted to the sealant game on the seals, even after changing the top 'in head' ones. I've even had to use sealant on the VW tubes I'm using with a decent dab on the threads to aid oil leak prevention I note with interest the way your pushrod tubes 'protrude' above the level of the head. With the Panda head they are flush making it easier for the lubricating oil to reach the followers I suppose. Just another subtle way the evolution of this engine progressed with time.
Ian.

 

[fiat500]

I note with interest the way your pushrod tubes 'protrude' above the level of the head. With the Panda head they are flush making it easier for the lubricating oil to reach the followers I suppose. Just another subtle way the evolution of this engine progressed with time.

Thank-you Ian; I didn't know that and perhaps it's mod that might be worth trying. But I'll save it for a future engine; I hate to think what the in-situ grinding process would do to the engine.

Like you, I think carefully about each component or process as I progress and I'm not afraid to try new ways of doing things rather than glibly replicating the way things might always have been perceived to be done.

Progress is slow but steady because I have lots of other things that need doing; even Covid-19 lockdown doesn't give me enough time to achieve what I would like to!

Today I measured the rocker-shaft for wear. I have three spare ones of these in addition to a few still bolted to engines! I've noted before, even though the ones for the 110F and 126 engines look the same, they are embossed with the type of engine they came from. The setup actually removed from this engine when working is the least worn. You measure the internal diameters of the rockers and the external diameter of the shaft. Subtract the latter from the former in each case and the clearance this gives needs to be less than 0.15mm.; it was well below this and closer to the clearance as new.

So the pushrods can now be put back and the tappets set up.

I've also dug out the correct spacer for the fuel-pump, so this can now be replaced; you can see just how much thicker it is than the one from a 499 engine. This was one of the changes which was intended to and in my experience actually does contribute to a reduced tendency for the petrol to vaporise before reaching the carburettor on the later design.

I have the exhaust elbows to fit and a de-rusted sump now waiting for paint....#gettingthere .

 

[Toshi 975]

Hope you can find the right fuel pump push rod otherwise you are short of a squirt of gas ?
Probably some syndrome I have but I always arrange those push rod tubes in the way you have for the symmetry and always keep twisting them as you torque down the head to ensure that the seals seem happily seated and no pinching. So the question is was the engine originally designed to allow a small amount of oil to flow through those small cut outs from oil puddling in the depressions to lube the cam followers with the bulk of the oil flow going down the deeper central cavity where the oil feed pipe runs up to the rockers.
How wonderful it would be if the original designers of the 500 were available to answer questions about their designs.