Measuring Valve Tappet Adjustment

[kkemerait]

Can someone detail for me the correct procedure for adjusting/measuring the valve tappet clearance on a 1978 Fiat 124 spider. I have the tappet adjustment tool, but nothing else....the "guide" on IAP's site simply refers you to the "correct" procedure as detailed in the manual, but talks about things such as "pre-loading". I am not a mechanic .. so if anyone can point me to a good step by step procedure which includes what to remove (belts? plugs?, etc.) and how to go about making changes I would appreciate it.

Thanks in Advance.

 

[s130]

You don't say what your Spider Engine is. Almost certainly the venerable Fiat Twin Cam Engine which means that tappet clearance adjustment is via shims.

Unlike a rocker arm mechanism as Ford and others used, the Fiat TC engine uses a "true overhead cam design" where the cam shaft lobes operate directly onto the top of the valve stems with no levers or rods involved.

To do this the cam followers a 'bucket' shaped so that they can hold a round shim of the correct thickness to adjust the gap between the top of the shim and the back of the camshaft lobe.

Take a look here [ame]http://en.wikipedia.org/wiki/Overhead_camshaft[/ame]

Back to your question.

To change the shims (adjust the clearance) you need the following tools

1) A suitably profiled lever to despress the valve
2) A suitably profiled tool to hold the vale in the despressed position
3) Shim pliers or other means of removing the shims
4) A micrometer (in mm). This will probably be required as over time the shim size etch markings get rubbed off.

Note! Fiat have produced several tools over the years for doing this. One of there last designs was just locking tool to hold the valve down. The camshaft was use to depress the valve, tool inserted and engine/camshaft wound back.

Now for the procedure: (variations exist)

1) Remove rocker and gasket. Do this on level ground after the engine has stood still for 15 or so minutes and has near enough returned to ambient temperate. I normally leave the car oevernight. Level is important as the Fiat cam design is such that the shaft are bathed in oil an if the car is no level oil will spill out when you remove the cam covers.

2) Remove the spark plugs

3) Syphon off / remove as much oil as you can from the cam carriers so you can see the tops of the valve followers & shims

4) Set handbrake and jack up front offside wheel till it is about 1 inch clear of the ground and select 4th gear .... now the fun starts

5) Starting with either the inlet or exhaust camshaft rotate the wheel forward and watch the chosen camshaft till the ONE of the cam lobe tips is exactly point upwards and perpendicular to the valve shim base. NOTE! the valves are inclined so the lope tip will not be pointing vertically up compared to the ground.

6) Using a feeler guage measure the gap between the back of the lobe and the shim. You need to note the gap (mm) and valve number correctly.

7) Now repeat for all remaining valves on both inlet and exhaust camshaft.

8) Now rotate again till the first valve you started with is in a position to be measured again. If the gap is ok then move on in sequence till the first out of spec gap is found.

9) Now depress the valve fully with the lever tool and whilst depressed insert the clamp/depression retaining tool to hold the value down in the locked position. NOTE! You will see that there are diagonally opposite cut-outs in the cam follower/buck. Using a bradawl or small screw driver rotate the follower so you have prising access to these cutouts. Depending on the tools you have will need to align the cutout PRIOR to depressing and locking the valve.

10) We now have to remove the valve shim. Using a soft metal bradawl or small screw driver you need to prise the shim out of the bucket. Note this is not easy due to oil suction effects. I personally gently blow air (from a compressor but using a straw and your lungs does work) to disperse the oil from under the shim.

11) Having removed the shim, flip it over an read the shim size or measure with the micrometer.

12) Now the calculation. If the gap is supposed to be 1mm but is 0.8mm and the shim is 3.55mm then you require a new shim off 3.35mm. i.e. gap has to be increased by 0.2mm so shim has to be reduce by 0.2mm. The shims come in a ranges of sizes. Luckily for all Fiat mono cam and twin cam engines all shims are of the same type.

13) You are unlikely to have the correct shim in stock so you will have to replace this shim (before replacing a shim massage it with engine oil!) and then move on to the next valve. Also mentally note the condition (bot top and bottom sides of the shim) and wear on the shim. This comes with practice and combined with new shim purchase records allows shims to be safely re-used. ALWAYS not the shim size value by valve when you replace them!

14) Move to next up for adjustment and repeat steps 10 to 13

When you get to the last valve you will now have a map of valve number, valve gap, current shim and required shim. Scanning your list you may find that shims can be moved between valves to obtain correct clearances and minimise the number of new shims that are required to be purchased. ALWAYS not the shim size value by valve when you replace them!

The first time is always the longest and hardest. After that you will have a map of shims, gaps etc. by valve number. Next time all you have to do is measure the gaps and because you know the current shim size for every valve you can calculate the new shims required and work out a suitable shuffle pattern.

Hope this all makes sense, and sorry it was so long winded......

 

[kkemerait]

Nick, that was awesome, thank you for the detailed response. Not knowing how long it might be before a response I ventured out and took a peek getting the current gaps but not removing or measuring the shims (I don't mind doing it again next weekend .. practice makes perfect!) ... here's what I found... and yes 1.8L DOHC

#1 - 0.203
#2 - 0.457
#3 - 0.457
#4 - 0.254

Next weekend I'll measure the existing shims and order new ones where needed. I measured each one twice to be certain and will repeat again when I change them. Those are the intake side .. exhaust next week.

 

[s130]

There are variations between 1600cc, 1800cc and 2000cc models but the general rule of thumb is:

Inlet 0.40 +/- 0.05mm
Exhaust 0.50 +/- 0.05mm

I see you only mention 4 values and don't specify if inlet or exhaust.

Shimming these engines is quite educational and theraputic. Actually brings you nearer to the real understanding and workings of an engine that the usual changing of oil, air and fuel filters will never bring.

 

[grimwau]

nick, that was awesome, thank you for the detailed response. Not knowing how long it might be before a response i ventured out and took a peek getting the current gaps but not removing or measuring the shims (i don't mind doing it again next weekend .. Practice makes perfect!) ... Here's what i found... And yes 1.8l dohc

#1 - 0.203
#2 - 0.457
#3 - 0.457
#4 - 0.254

next weekend i'll measure the existing shims and order new ones where needed. I measured each one twice to be certain and will repeat again when i change them. those are the intake side .. Exhaust next week.

i see you only mention 4 values and don't specify if inlet or exhaust.

lol.

 

[s130]

There are variations between 1600cc, 1800cc and 2000cc models but the general rule of thumb is:

Inlet 0.40 +/- 0.05mm
Exhaust 0.50 +/- 0.05mm

I see you only mention 4 values and don't specify if inlet or exhaust.

Shimming these engines is quite educational and theraputic. Actually brings you nearer to the real understanding and workings of an engine that the usual changing of oil, air and fuel filters will never bring.

This rule of thumb by the way may with high lift cams (like the Strada Abarth has) make the engine sound quite tappety. To overcome this then setting the clearances to the lower limits +0.05 I have found to be perfectly ok.

i.e.

Inlet 0.35 to 0.40
Exhaust 0.45 to 0.50

Most of the noise will come from the exhausts valves so these are the ones to focus on if you have a noise issue.

 

[kkemerait]

OK, let me ask a few more ...

#1 - What am I actually affecting by adjusting the tappet clearance and is there any benefit to going outside of the recommended specs?

#2 - What causes each valve tappet to be of different sizes in the first place?

#3 - I assume that wear and tear would cause the tappet clearance to increase over time, not to decrease. So am I right in assuming that because valve's 1 & 4 have only half the required clearance 0.203 & 0.254 respectively that they were not done correctly in the first place?

 

[grimwau]

OK, let me ask a few more ...

#1 - What am I actually affecting by adjusting the tappet clearance and is there any benefit to going outside of the recommended specs?

Allowing the engine to breathe properly, the only reason for going outside the recommended clearances would be if different camshafts were fitted.

#2 - What causes each valve tappet to be of different sizes in the first place?

Tolerances, even from new can vary widely, even blueprinted engines still differ.

#3 - I assume that wear and tear would cause the tappet clearance to increase over time, not to decrease. So am I right in assuming that because valve's 1 & 4 have only half the required clearance 0.203 & 0.254 respectively that they were not done correctly in the first place?

Wear and tear are the main factor but not in the way you mean. As long as the cam lobes aren't worn (case hardening still intact) then nothing really changes. The shims don't wear as such nor do the tappets as long as the oil/filter are changed regularly using recommended or higher spec fully synthetic lubricants.

Although noisy tappets are the result of either wear on the cam lobes, cam bearings, tappets etc. making the gaps wider as things gradually wear. The reason for the gaps being smaller is probably due to the valve heads wearing into the valve seats in the cylinder head after opening and being slammed shut by the valve springs many millions of times. This effectively moves them closer to camshaft hence the reduced clearance.

Hope you can understand my ramblings as I am not quite as good as explaining as S130.

 

[s130]

The BIGGEST wear (assuming good shims, camshaft, & oil) is actually called "valve recession".

Every time the valve closes against the seat impact and very slight rotation take places. This wears the surfaces. Also every time the valves open then there is a small amount of material adhesion that has to be broken. This results a material being remove from both the valve and valve seat.

The net result is that over time, on Fiat TC engines, the valve clearance gaps actually get SMALLER.

Fuel, lead vs unleaded play a major part in valve and valve seat wear. The lead in leaded fuel coats the valve & seat with a soft metal lining protects both valve and seat from both closure impact and opening wear effects. For unleaded fuel one requires hardened valve seats and valves.

If valve clearance get to small then seat temperatures rise and wear gets worse. Given time and as zero clearance approaches the valves will not shut properly and both valve and seat will massively overheat, causing initially pitting as the very hot metal surfaces are force separated during valve opening. This is followed by valve seat burning as during the engine ignition cylce the hot and explosive gasses are force through very small gaps and thus cause more damage/erosion.

Hope this helps with you questions.

 

[kkemerait]

Thanks all, great explanations...I'll be measuring today, then ordering new shims and replacing this weekend. I'll be happy to take photos or notes if anyone else is interested in seeing. Thanks again!

 

[maddogmorg]

4) Set handbrake and jack up front offside wheel till it is about 1 inch clear of the ground and select 4th gear .... now the fun starts

*cough* the 124 was rwd, so you'd jack up the rear.

 

[s130]

*cough* the 124 was rwd, so you'd jack up the rear.

And so it is. Unless one has very long arms makes life a little more difficult.

However I suspect, unlike front wheel drive cars there is room at the front of the engine to get a socket and ratchet bar on the crank pulley to manually rotate the engine.

 

[grimwau]

:idea: Alternatively you can always put car in gear (plugs out makes it easier) and just push the car gently backwards whilst watching the cams.

 

[maddogmorg]

And so it is. Unless one has very long arms makes life a little more difficult.

However I suspect, unlike front wheel drive cars there is room at the front of the engine to get a socket and ratchet bar on the crank pulley to manually rotate the engine.

:doh: just call me Mr tickle!

No! not that one!

this one

 

[s130]

:idea: Alternatively you can always put car in gear (plugs out makes it easier) and just push the car gently backwards whilst watching the cams.

You should have saind 4th/5th gear and move car forwards. If it best never to rotate an engine backwards. On some Ferraris this can wreck the engine.

ALWAYS rotate the engine forwards. Make it a habbit even if reverse rotation would never cause a problem.

Pushing the car backards would require reverse gear to be selected and the gearing would be such that you could not move the car by hand anyway.

 

[kkemerait]

Wow! After all the great advice, waiting for good weather, today arrived...took off the valve covers, did all the measurements, removed the spark plugs, etc. etc. only to discover that the wonderful valve adjustment tool I purchased from IAP and manufactured somewhere in Europe for $45 was sized incorrectly and thus no matter how you tried to place it .. it overlapped onto the shim itself and was useless! (the width between the two prongs was too narrow by roughly 1/16"). Arrrrrrgh ... Anyone else have a similar problem with that tool or am I just lucky?

 

[s130]

Can you post link to IAP and picture of the tool? Does the tool have any markings?

What puzzles me is that I thought all Fiat valve bucket followers were the same diameter as are the shims. The only changes Fiat made in the tool retainer design was to accomodate closely splaced valve where the edge of a two pronged tool would overlap the one next to it.