Technical Valve clearance question

[smahaley]

I have rebuilt a 1978 124 motor (1.8) and have the following question:

I finally have a valve adjustment tool and have checked clearances twice - noting that I installed new valves. I get clearances that are all “loose” by .001 - .004 inches, with one exhaust valve that is “tight” by .005. There is one intake valve that is loose by a full hundredth (.010).

The manual suggests .017 for intake and .019 for exhaust.

How close do I need to get? Would .002 difference be detrimental?

Thanks in advance!

 

[Slotman]

I'm sorry I'm not offering advice here, but I'm curious of the same question as I want to replace my cams with sport cams...I can say as a life long air cooled vw fan, sometimes keeping the tolerances as close as possible matter, on my vw I wouldn't even adjust the valves unless the motor sat cold for 24 hrs, and then, the clearance is .006.....hopefully someone will chime in here with sage advice! I'm also wondering is there a such thing as a
"Box o shims" that we can buy to insure having just the right ones needed?

 

[smahaley]

I'm sorry I'm not offering advice here, but I'm curious of the same question as I want to replace my cams with sport cams...I can say as a life long air cooled vw fan, sometimes keeping the tolerances as close as possible matter, on my vw I wouldn't even adjust the valves unless the motor sat cold for 24 hrs, and then, the clearance is .006.....hopefully someone will chime in here with sage advice! I'm also wondering is there a such thing as a
"Box o shims" that we can buy to insure having just the right ones needed?

Thanks, and I too had a couple of air-cooled VWs and was quite familiar with valve adjustments . And yes you can buy a whole kit of shims - if you want to spend a bunch - which I don’t! I might just buy 2 to fix those with the greater gaps / tightness….

 

[smahaley]

Thanks, and I too had a couple of air-cooled VWs and was quite familiar with valve adjustments . And yes you can buy a whole kit of shims - if you want to spend a bunch - which I don’t! I might just buy 2 to fix those with the greater gaps / tightness….

I may have found an answer in a post from 2010 or so: The writer suggests a + or - .05 mm as tolerance for shim / lobe gap. That translates to .002 inches, which helps me a lot! That means I will only really need to replace 3 shims... now for more math to figure the sizes....

 

[s130]

For the all Fiat overhead cam engines (mono and twin cams) with shims then I've never seen values other than:

Inlet : 0.45mm +/- 0.05mm
Exhaust : 0.50mm +/- 0.05mm

Now on the Starda/Ritmo Abarth 130TC 1998cc it has high lift cams from the factory and the normal 0.45 & 0.50 mm settings are quite noisy / tappet y.

When it set the clearances I take 0.05 off, so:

Inlet : 0.40mm +/- 0.05mm
Exhaust : 0.45mm +/- 0.05mm

and preferably on exactly or on the tighter side:

Inlet : 0.35mm to 0.4mm
Exhaust : 0.4mm to 0.45mm

The car / engine has done over 6000 miles of motor sport / track / sprinting new in 1988 and all is fine. No valve problems or recession.

It has been argued / suggested that for Fiat engines not specifically designed for unleaded fuel in the US market the EU / leaded engines already have harder than normal seats so running unleaded is not a real problem (well excluding motor sport and continuous full bore driving) and reduced valve clearances actually help due to the lower valve head to valve seat dynamic impacts.

Summary. Stick to recommended values but if noise is a problem then take 0.05mm off. Perfectly OK. With this in mind if targetting the default values you can get within the -0.05 tolerance then don't worry!

 

[smahaley]

For the all Fiat overhead cam engines (mono and twin cams) with shims then I've never seen values other than:

Inlet : 0.45mm +/- 0.05mm
Exhaust : 0.50mm +/- 0.05mm

Now on the Starda/Ritmo Abarth 130TC 1998cc it has high lift cams from the factory and the normal 0.45 & 0.50 mm settings are quite noisy / tappet y.

When it set the clearances I take 0.05 off, so:

Inlet : 0.40mm +/- 0.05mm
Exhaust : 0.45mm +/- 0.05mm

and preferably on exactly or on the tighter side:

Inlet : 0.35mm to 0.4mm
Exhaust : 0.4mm to 0.45mm

The car / engine has done over 6000 miles of motor sport / track / sprinting new in 1988 and all is fine. No valve problems or recession.

It has been argued / suggested that for Fiat engines not specifically designed for unleaded fuel in the US market the EU / leaded engines already have harder than normal seats so running unleaded is not a real problem (well excluding motor sport and continuous full bore driving) and reduced valve clearances actually help due to the lower valve head to valve seat dynamic impacts.

Summary. Stick to recommended values but if noise is a problem then take 0.05mm off. Perfectly OK. With this in mind if targetting the default values you can get within the -0.05 tolerance then don't worry!

Thank you very much!!

 

[Twink80]

Thank you very much!!

So for a bit of interest I looked through my collection of Twincam related workshop manuals for Fiat 131, Lancia Beta, Fiat 124 and Guy Croft, photo attatched
The specs are quite varied, all the engines have slightly different cam profiles and may have different requirements for tappet noise etc. The smaller the clearance the greater the valve lift.
I went with Guy Crofts recomendation of 16th In & Ex and achieved a actual spread of 12-14 on Ex and 15-17th on Inlet (argueably this would be better the other way round as ex valve expands more) but I didn’t want to spend a load more time and money for negligible gains. The engine runs great like this

 

[Twink80]

So for a bit of interest I looked through my collection of Twincam related workshop manuals for Fiat 131, Lancia Beta, Fiat 124 and Guy Croft, photo attatched
The specs are quite varied, all the engines have slightly different cam profiles and may have different requirements for tappet noise etc. The smaller the clearance the greater the valve lift.
I went with Guy Crofts recomendation of 16th In & Ex and achieved a actual spread of 12-14 on Ex and 15-17th on Inlet (argueably this would be better the other way round as ex valve expands more) but I didn’t want to spend a load more time and money for negligible gains. The engine runs great like this

Also to note Lancia Twincams typically produce more power and torque than the Fiat equivalent

 

[smahaley]

So for a bit of interest I looked through my collection of Twincam related workshop manuals for Fiat 131, Lancia Beta, Fiat 124 and Guy Croft, photo attatched
The specs are quite varied, all the engines have slightly different cam profiles and may have different requirements for tappet noise etc. The smaller the clearance the greater the valve lift.
I went with Guy Crofts recomendation of 16th In & Ex and achieved a actual spread of 12-14 on Ex and 15-17th on Inlet (argueably this would be better the other way round as ex valve expands more) but I didn’t want to spend a load more time and money for negligible gains. The engine runs great like this

Wow - that IS quite a variety of ranges! Thanks for the input - I think I’m going to replace 3 shims in order to get things within the Haynes spec (+ / - ). I have a functioning micrometer now, and need to measure each of them just for my notes so I’ll be spending more quality time with the top end….holy moly I hope this thing runs when I’m done!

 

[sgkent]

Hi -just had some time on my hands this morning and dropped by to see who needed help. My background is having owned a 1973 124 spider back in the 1970's for some wonderful 150,000 miles, and 1974 124 coupe. I worked as a Fiat, Lancia, and Ferrari technician on a whim for about two years, and also worked in a racing machine shop that built FI and Score engines for the Unsers and others. My masterpiece was a Ferrari Dino engine I remanufactured for a friend, Enzo Ferrari gifted the parts out of his private collection when we could not locate them in the States for purchase. I also was crew chief and technician on two SCCA FP 124 spiders. One won a championship in FP. That said, in answer to the valve specs. If you are adjusting them you do it right and get the clearance dead on the number that is spec'd for the engine. You make record of any changes to keep track of trends in case a valve stretches or a cam profile changes. To be candid, and not an ass, anyone who is going to adjust valves, needs to have access to a good number of shims to work with, preferably the whole kit. Today you cannot just drop by a dealer and pick up some shims like we could back then. Normally the range of shims needed fall into a small range, meaning that the whole kit might go from A to Z but the shims in normal use are say G - R. I use letters to illustrate the concept, I know that the shims don't have letters. A good micrometer, the valve tool, and feeler gauge are needed. NEVER use the starter to bump the cam or you may hold a valve open and bend it if there is a piston strike. Ask me how I know. Use a socket and a breaker bar to turn the engine over. Don't try to fake it. If you are going to do it, do it right.

 

[s130]

For the all Fiat overhead cam engines (mono and twin cams) with shims then I've never seen values other than:

Inlet : 0.45mm +/- 0.05mm
Exhaust : 0.50mm +/- 0.05mm

Now on the Starda/Ritmo Abarth 130TC 1998cc it has high lift cams from the factory and the normal 0.45 & 0.50 mm settings are quite noisy / tappet y.

When it set the clearances I take 0.05 off, so:

Inlet : 0.40mm +/- 0.05mm
Exhaust : 0.45mm +/- 0.05mm

and preferably on exactly or on the tighter side:

Inlet : 0.35mm to 0.4mm
Exhaust : 0.4mm to 0.45mm

The car / engine has done over 6000 miles of motor sport / track / sprinting new in 1988 and all is fine. No valve problems or recession.

It has been argued / suggested that for Fiat engines not specifically designed for unleaded fuel in the US market the EU / leaded engines already have harder than normal seats so running unleaded is not a real problem (well excluding motor sport and continuous full bore driving) and reduced valve clearances actually help due to the lower valve head to valve seat dynamic impacts.

Summary. Stick to recommended values but if noise is a problem then take 0.05mm off. Perfectly OK. With this in mind if targetting the default values you can get within the -0.05 tolerance then don't worry!

That last bit should have read: With this in mind if when targeting the default values you CAN'T get within the -0.05 tolerance then don't worry!

 

[smahaley]

That last bit should have read: With this in mind if when targeting the default values you CAN'T get within the -0.05 tolerance then don't worry!

Thanks very much - I appreciate the details!

 

[s130]

Hi -just had some time on my hands this morning and dropped by to see who needed help. My background is having owned a 1973 124 spider back in the 1970's for some wonderful 150,000 miles, and 1974 124 coupe. I worked as a Fiat, Lancia, and Ferrari technician on a whim for about two years, and also worked in a racing machine shop that built FI and Score engines for the Unsers and others. My masterpiece was a Ferrari Dino engine I remanufactured for a friend, Enzo Ferrari gifted the parts out of his private collection when we could not locate them in the States for purchase. I also was crew chief and technician on two SCCA FP 124 spiders. One won a championship in FP. That said, in answer to the valve specs. If you are adjusting them you do it right and get the clearance dead on the number that is spec'd for the engine. You make record of any changes to keep track of trends in case a valve stretches or a cam profile changes. To be candid, and not an ass, anyone who is going to adjust valves, needs to have access to a good number of shims to work with, preferably the whole kit. Today you cannot just drop by a dealer and pick up some shims like we could back then. Normally the range of shims needed fall into a small range, meaning that the whole kit might go from A to Z but the shims in normal use are say G - R. I use letters to illustrate the concept, I know that the shims don't have letters. A good micrometer, the valve tool, and feeler gauge are needed. NEVER use the starter to bump the cam or you may hold a valve open and bend it if there is a piston strike. Ask me how I know. Use a socket and a breaker bar to turn the engine over. Don't try to fake it. If you are going to do it, do it right.

Thankfully I have a fairly large personal stock of shims and three different Fiat tools depression and hold down the bucket followers.

I also you my own table to track shims by valve. e.g.

(29) Gaps set to 0.35 inlet, 0.45 exhaust - no adjustments required

Valve/Cyl. 1 2 3 4 1 2 4 4 SPEC.
Type I I I I E E E E I=0.40
Gap 0.35 0.35 0.35 0.35 0.45 0.45T 0.45 0.45 E=0.50
Old Shim 4.50 4.35 4.45 4.35 4.30 4.25* 4.35 4.20
Set Shim X X X X X X X X
Set Gap 0.35 0.35 0.35 0.35 0.45 0.45T 0.45 0.45

The 0.nnT indicates a TIGHT feeler gauge setting. The 4.nn* indicates that the shim has no printed/marked size. In the above example Set Shim X indicates that no new shim value was set.

Every time I check clearances I us the above example table so I can just rotate the engine, measure all the current gaps and then work out what new shim values I need. Often shims can be shuffled around as well as new/old ones used from stock. Makes life a lot easier and quicker

 

[smahaley]

Thankfully I have a fairly large personal stock of shims and three different Fiat tools depression and hold down the bucket followers.

I also you my own table to track shims by valve. e.g.

(29) Gaps set to 0.35 inlet, 0.45 exhaust - no adjustments required

Valve/Cyl. 1 2 3 4 1 2 4 4 SPEC.
Type I I I I E E E E I=0.40
Gap 0.35 0.35 0.35 0.35 0.45 0.45T 0.45 0.45 E=0.50
Old Shim 4.50 4.35 4.45 4.35 4.30 4.25* 4.35 4.20
Set Shim X X X X X X X X
Set Gap 0.35 0.35 0.35 0.35 0.45 0.45T 0.45 0.45

The 0.nnT indicates a TIGHT feeler gauge setting. The 4.nn* indicates that the shim has no printed/marked size. In the above example Set Shim X indicates that no new shim value was set.

Every time I check clearances I us the above example table so I can just rotate the engine, measure all the current gaps and then work out what new shim values I need. Often shims can be shuffled around as well as new/old ones used from stock. Makes life a lot easier and quicker

Super helpful: I made a chart as well; my first rounds of measurement I put down in inches. I think I want to start over and mark everything in metric, as the shim values are marked as such. I did note that one or two of my shims had no number markings on them (may have worn off?). Also only just procured a micrometer, so when I get back to this project next week I’ll re-measure everything and use your chart: I think I may only need to buy 3 or 4 shims, but we’ll see. I saw a “shim kit” listed for $300 - no thank you!

 

[s130]

I gather that Volvo 240, 740, 760, 940, 960, 360 models fitted with 4 cylinder 8 valve OHC B19, B21, B23, B200, B230 "Redblock" petrol engines also use the same 33mm diameter shims. Worth checking if Fiat/Lancia ones are hard to get in you location.

 

[smahaley]

I gather that Volvo 240, 740, 760, 940, 960, 360 models fitted with 4 cylinder 8 valve OHC B19, B21, B23, B200, B230 "Redblock" petrol engines also use the same 33mm diameter shims. Worth checking if Fiat/Lancia ones are hard to get in you location.

Oooh interesting - thanks @s130 - there are 3 parts houses here in the US that I have access to - and there’s always eBay. Will see when I get back to it next week!

 

[124BC1]

Also to note Lancia Twincams typically produce more power and torque than the Fiat equivalent

So said the Lancia sales people!!

Would you buy a Lancia if the equivalent Fiat engine produced more power??

 

[124BC1]

Oooh interesting - thanks @s130 - there are 3 parts houses here in the US that I have access to - and there’s always eBay. Will see when I get back to it next week!

Yeah, the usual suspects all list the various sized Fiat shims singly at reasonable cost c.$3-$4 each.

Also, bear in mind that having fitted new valves and lapped them into their seats, that things may settle down with some use and some of the valves may need re-adjusting (or not ) - so I wouldn't try to get ultra-precise with the initial settings.

 

[124BC1]

So for a bit of interest I looked through my collection of Twincam related workshop manuals for Fiat 131, Lancia Beta, Fiat 124 and Guy Croft, photo attatched
The specs are quite varied, all the engines have slightly different cam profiles and may have different requirements for tappet noise etc. The smaller the clearance the greater the valve lift.
I went with Guy Crofts recomendation of 16th In & Ex and achieved a actual spread of 12-14 on Ex and 15-17th on Inlet (argueably this would be better the other way round as ex valve expands more) but I didn’t want to spend a load more time and money for negligible gains. The engine runs great like this

Re your chart of valve clearances, I believe the Mirafiori (8 thou/0.20mm) valve clearances refer to the OHV (i.e. pushrod) engine, not the t/cam engine.

I've always thought the older fiat t/cam engines sound 'tappety' with the stock valve clearances. Compared to other t/cam engines, especially Japanese m/cycle engines the valve clearances seem enormous. I used to 'play around' with these engines, once, having checked how much clearance remained with the engine really hot, I even reduced the valve clearances in & ex by 10 thou (0.010 / 0.25mm) - the engine started and ran just fine, was much quieter and even seemed 'livelier'. As you say above, smaller clearances increase the valve lift, they also change the valve timing (both inlet and exhaust valves now open earlier and close later, increasing the duration and overlap), push the pistons closer to the pistons, possibly risk the valve springs becoming coilbound? - so a bit like fitting slightly 'sportier' cams.

However reducing valve clearances significantly is not a good idea!
One of the reasons why Fiat use such large valve clearances is for valve cooling especially the exhaust valves - these lose only a little heat via the valve stems and rely on being closed against their valve seats to transfer excessive heat and prevent overheating/failure. The inlet valves get a blast of cool air/fuel vapour every time they open which helps regulate their temperature. Ever noticed that often inlet and exhaust valves are made from different materials, with the exhaust valve having the more heat-resistant metal, or the way carbon build-up on the valves is different, typically black and softish on the inlet valves, brown/almost white and fried rock-hard on the exhaust valves....

I stick to the manufacturer's recommended valve clearances (their Engineers know way more than me!), but aim for the lower figure allowed. I think the 2 thou (0.002"/0.05mm - I hope I've converted these figures correctly) tolerance allowed is because the shims come in 2 thou increments

 

[Slotman]

124bc1 you are a walking and talking encyclopedia of knowledge I hope you will please keep sharing with us!