Technical Valve guide seals

[H A]

Hi, have got my spare 500L head apart as I was giving it a skim. How serious are the cracks between valve seats? Have looked up all the threads that I can find and there is a difference of opinion. I am going with valve seats are deep so don't worry.
I am also curious how a 6x2mm o-ring on the valve stem will actually do any thing as it is floating and not seated on the valve guide as later motors.
Some people say you need 2, some say 4. I cant see how they actually seal anything.

thanks

 

[the hobbler]

Hi, have got my spare 500L head apart as I was giving it a skim. How serious are the cracks between valve seats? Have looked up all the threads that I can find and there is a difference of opinion. I am going with valve seats are deep so don't worry.
I am also curious how a 6x2mm o-ring on the valve stem will actually do any thing as it is floating and not seated on the valve guide as later motors.
Some people say you need 2, some say 4. I cant see how they actually seal anything.

thanks
View attachment 419506

The 'O' ring seal works by preventing oil running down the valve stem. It is not 'floating'----When fitting the valves, the seal is pushed as far down the stem towards the guide as it can be---it eventually will sit at at a position on the valve stem at a position up against the valve-guide when the valve is fully open. I have only ever fitted 1 seal, and never had an 'oil-burning' problem.
If that is your 500L head on the picture, you would seem to have skimmed a great deal off it, to the point where the 'blown-head-gasket-ring' has been totally removed. The whole point of that ring is to prevent exhaust fumes coming into the vehicle's heater system, by venting any exhaust fumes round that ring and then out through the HOLLOW bolt that holds the shrouding on at the ends of the cylinder head (just above the exhaust on your picture)

 

[H A]

What are you talking about? It is my 1971 head on my milling machine. I took 10 thou off to clean it up, there was never a head gasket ring, I think you are confused with another later model.

So the o-rings are as I said "floating" they finds their best location on the valve stem when the valve opens.
Why have you only fitted one seal? workshop manual says only fit on the inlet valves so 2 required, but some say fit to all valve stems.

 

[the hobbler]

What are you talking about? It is my 1971 head on my milling machine. I took 10 thou off to clean it up, there was never a head gasket ring, I think you are confused with another later model.

So the o-rings are as I said "floating" they finds their best location on the valve stem when the valve opens.
Why have you only fitted one seal? workshop manual says only fit on the inlet valves so 2 required, but some say fit to all valve stems.

There is DEFINATELY an 'exhaust-ring' on the 500L head----If your head came without that ring, 1 of 2 things has occured. (1) it is not a 500L head, but a very early head--unlikely, or (2) a previous owner has already skimmed that head. The only 'later' model was the 500R, which used a 594cc '126' engine. If you wish to contact me direct ( [email protected] ) I will send you a photo of a 500L head---complete with 'exhaust ring'

 

[H A]

Brand New Cylinder Head & Gaskets Complete - Classic Fiat 500 D/F/L 499cc - Classic Fiat 500 D/F/L (499cc Engine) | Italian Car Parts Specialists

Brand New Cylinder Head & Gaskets Complete - Classic Fiat 500 D/F/L 499cc - Classic Fiat 500 D/F/L (499cc Engine) - Engines and Cylinder Heads - Brand New Genuine Fiat Complete with Valves,Springs etc and ready to install Supplied with Head Gasket Se

www.ricambio.co.uk

You might want to check your parts book for part number 4240095

 

[H A]

And cast for a 26mm carb

 

[H A]

New one available in Italy

 

[Bounding Bambino]

This is a interesting observation if it is the case. Typically i have seen that the majority of stock 500's head have the blow by ring. With that said though.. I wonder if there was ever a production change on a batch of the cars that instead solely used the ring on the cylinder/jug side, and solid on the head side. Would be curious to see if both are a possibility. The new one you posted on ebay, doesn't look like its been shaved at all/much (gotta take things being listed new on ebay as a grain of salt) however im inclined to believe it is. As there is still the combustion chamber lip on the shallow side of the combustion chamber. Typically that lip disappears as the head is shaved, and usually disappears around the same depth of material removal as the blow by groove +/- a few mm. Its hard to come accross a engine that hasnt been shaved once or twice in its life..

Now as far as valve guide seals go, everyone has their own take on it. Personally i wasn't sold on the factory style floating o-ring, it just didn't seem mechanically effective to me, but to each their own. On my build i did modern viton push on stem seals on the intake valves only. Typically what ive seen and done on other engine builds is just put the seal on the intake valve to prevent smoking on startup and smoking from prolonged idle. If those dont bother you at all, then forgo the stem seal and extend the life of your valve guides. As for exhaust valves, i would typically not install them on a older style engine. The exhaust valve sees a lot of temperature and wear compared to the intake. And any oil it can get the better. The exhaust side of the valve is not under vacuum unlike the intake, and wont typically suck in oil down the guide during operation. I think i posted the part number for the intake valve stem seal i used. Iirc i had to deck the guide height to provide clearance for the guide spring retainer which all depends on your setup. But other then that it was a simple install.

Due to the fact that these classics dont see the daily wear and tear that they saw when in daily use. Throwing a set of seals on the exhaust valves wouldn't hurt for a few thousand km a year.

 

[fiat500]

This is a interesting observation if it is the case. Typically i have seen that the majority of stock 500's head have the blow by ring. With that said though.. I wonder if there was ever a production change on a batch of the cars that instead solely used the ring on the cylinder/jug side, and solid on the head side. Would be curious to see if both are a possibility. The new one you posted on ebay, doesn't look like its been shaved at all/much (gotta take things being listed new on ebay as a grain of salt) however im inclined to believe it is. As there is still the combustion chamber lip on the shallow side of the combustion chamber. Typically that lip disappears as the head is shaved, and usually disappears around the same depth of material removal as the blow by groove +/- a few mm. Its hard to come accross a engine that hasnt been shaved once or twice in its life..

Now as far as valve guide seals go, everyone has their own take on it. Personally i wasn't sold on the factory style floating o-ring, it just didn't seem mechanically effective to me, but to each their own. On my build i did modern viton push on stem seals on the intake valves only. Typically what ive seen and done on other engine builds is just put the seal on the intake valve to prevent smoking on startup and smoking from prolonged idle. If those dont bother you at all, then forgo the stem seal and extend the life of your valve guides. As for exhaust valves, i would typically not install them on a older style engine. The exhaust valve sees a lot of temperature and wear compared to the intake. And any oil it can get the better. The exhaust side of the valve is not under vacuum unlike the intake, and wont typically suck in oil down the guide during operation. I think i posted the part number for the intake valve stem seal i used. Iirc i had to deck the guide height to provide clearance for the guide spring retainer which all depends on your setup. But other then that it was a simple install.

Due to the fact that these classics dont see the daily wear and tear that they saw when in daily use. Throwing a set of seals on the exhaust valves wouldn't hurt for a few thousand km a year.

From 500F onwards the "blow-by" device was by grooves on the tops of the barrels and exit ports on the head via appropriate holes in the gasket; @H A is correct and @the hobbler is mistaken. The 594 heads and I think the later 652 will have the groove, but I can't remember if that was also matched on the barrels. @Toshi 975 will know all the nuances. The image is one of my own from a genuine 69 F.

 

[Goldnrust]

When I was trying to work out if either of the 2 500cc cylinder heads I have, neither of which have the blow by ring, were standard I'm sure a read a thread talking about cylinder heads where it was confirmed that the 500cc D/F/L cylinder heads didn't have the blow by ring, but the 595cc and 650cc engines did. This would seem to be backed up by the various suppliers offering new 500cc heads with no ring.

Regarding the cracks, I also read up on this, if you search the forum there are some picture of other cracked cylinder heads. There were two issues with cracks, one is the risk of the crack opening up and allowing one of the valve seats to move /drop out causing a fairly major engine failure. The second was that if the cracks extend further down into the throat of the port, then you could have air leakage which could disrupt the fuel mixture.

If you have the tools on hand, then removing the valve seats, putting a nice V on the crakc, welding it up, machining back the weld and having new valve seats fitted would be the permanent fix.

Both my cylinder heads were cracked maybe not quite as obvious a crack as in yours but similar, neither extended down into the ports, so for now I'm going to risk it and hope for the best. Chances are it cracked thousands of miles ago and it'll all be fine... Worst case, good job I have a spare engine! haha.

Finally, valve stem seals. As far as I understood it, the O ring should go on after you have compressed the valve spring, between the spring top cap and the collets, see the picture I grabbed off google below. In this way it seals the top of the valve from the oil coming out of the rocker arm and the spring top cap creates a kind of umbrella for the valve stem with oil running down the outside of the spring. The valve stem is lubricated by oil vapour and splashes, but it's protected from the constant stream of oil coming out of the rocker. I have fitted valve stem seals to all 4 valves.

 

[fiat500]

What are you talking about? It is my 1971 head on my milling machine. I took 10 thou off to clean it up, there was never a head gasket ring, I think you are confused with another later model.

So the o-rings are as I said "floating" they finds their best location on the valve stem when the valve opens.
Why have you only fitted one seal? workshop manual says only fit on the inlet valves so 2 required, but some say fit to all valve stems.

I've debated this with Tom on a previous occasion and I'm sticking to my guns....they are pointless as floaters. I agree with @Bounding Bambino that they are probably better not used on exhausts.

594 Engine Rebuild | FIAT 500 (Classic)

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...

www.fiatforum.com

 

[fiat500]

When I was trying to work out if either of the 2 500cc cylinder heads I have, neither of which have the blow by ring, were standard I'm sure a read a thread talking about cylinder heads where it was confirmed that the 500cc D/F/L cylinder heads didn't have the blow by ring, but the 595cc and 650cc engines did. This would seem to be backed up by the various suppliers offering new 500cc heads with no ring.

Regarding the cracks, I also read up on this, if you search the forum there are some picture of other cracked cylinder heads. There were two issues with cracks, one is the risk of the crack opening up and allowing one of the valve seats to move /drop out causing a fairly major engine failure. The second was that if the cracks extend further down into the throat of the port, then you could have air leakage which could disrupt the fuel mixture.

If you have the tools on hand, then removing the valve seats, putting a nice V on the crakc, welding it up, machining back the weld and having new valve seats fitted would be the permanent fix.

Both my cylinder heads were cracked maybe not quite as obvious a crack as in yours but similar, neither extended down into the ports, so for now I'm going to risk it and hope for the best. Chances are it cracked thousands of miles ago and it'll all be fine... Worst case, good job I have a spare engine! haha.

Finally, valve stem seals. As far as I understood it, the O ring should go on after you have compressed the valve spring, between the spring top cap and the collets, see the picture I grabbed off google below. In this way it seals the top of the valve from the oil coming out of the rocker arm and the spring top cap creates a kind of umbrella for the valve stem with oil running down the outside of the spring. The valve stem is lubricated by oil vapour and splashes, but it's protected from the constant stream of oil coming out of the rocker. I have fitted valve stem seals to all 4 valves.

View attachment 419527

Finally someone agrees with me. Thank-you for the image @Goldnrust . See the link in my post that came just after yours.

 

[bugsymike]

Just to throw my oar in, two things .
The initial photo showing the crack between the valve seats I would be concerned that when hot the crack would relax the grip of the valve seat steel insert causing it to drop out of the aluminum cylinder head due to different expansion rates.
The other thing regarding O rings on valve stems, in the old days they were fitted to the inlets only, as the vacuum caused by the piston going down on the inlet stroke would cause any oil to be "sucked " into the combustion chamber. The O rings were more as a deflector than a perfect oil seal.
Obviously modern design is greatly improved and more efficient seals are fitted to all the valves.

 

[the hobbler]

Just to throw my oar in, two things .
The initial photo showing the crack between the valve seats I would be concerned that when hot the crack would relax the grip of the valve seat steel insert causing it to drop out of the aluminum cylinder head due to different expansion rates.
The other thing regarding O rings on valve stems, in the old days they were fitted to the inlets only, as the vacuum caused by the piston going down on the inlet stroke would cause any oil to be "sucked " into the combustion chamber. The O rings were more as a deflector than a perfect oil seal.
Obviously modern design is greatly improved and more efficient seals are fitted to all the valves.

I owe an apology to members of the Forum---I was under the impression that ALL 'F' and 'L' heads had the blow-by rings in the cylinder head---my source states (and it is a very reliable source0 that the 'break point' was March 1965. Before that engines (including the 110 and 110D) did NOT have the rings in the head, but after March '65 they did. However, knowing Fiat and their habit of using up parts (the 500R is a perfect example) this date may have some 'flexibility'

 

[H A]

Thanks for the apology.
I have just pulled the head on my 1973 500L that I have owned for 36 years, it has only done 51000 miles and engine has never been apart.
I believe it was one of the last 500Ls and has the 4240095 head.

When I pull the valves I will look closely at o-ring position and number.

 

[fiat500]

I owe an apology to members of the Forum---I was under the impression that ALL 'F' and 'L' heads had the blow-by rings in the cylinder head---my source states (and it is a very reliable source0 that the 'break point' was March 1965. Before that engines (including the 110 and 110D) did NOT have the rings in the head, but after March '65 they did. However, knowing Fiat and their habit of using up parts (the 500R is a perfect example) this date may have some 'flexibility'

What is your source that makes that claim in the face of reality. My 1969, untouched head, and the one just uploaded from a 1973, both lack the machined groove as do heads available from Axel Gerstl and Ricambio. The 499 combustion chamber is asymmetric and wouldnt lend itself to being machined in that way. I would like to see an image of one with the groove and then I will also apologise for being so assertive.

 

[H A]

Have popped the valves out, o-rings on all valves, just under collets, so not floating retained by groove in valve and collets.

Head in need of an overhaul, will replace valves and guides.

 

[Bleeding Knuckles]

It's amazing how many changes this engine series went through in it's life, I have two Panda heads Both had cracks between the valves on one cylinder. The 1983 head has the larger stem seals on the intake valve only, the later 1986 head has the seals on both valves!!! I vaguely remember it was to do with emissions in the early days - all part of the development process I suppose??
Ian.

 

[Toshi 975]

Have popped the valves out, o-rings on all valves, just under collets, so not floating retained by groove in valve and collets.


View attachment 419555View attachment 419556
Head in need of an overhaul, will replace valves and guides.

I have new valves & guides here if interested

 

[Toshi 975]