Technical Cam shaft replacement - is it an engine out job?

[the hobbler]

Good point.

I always use recommend the use of the 'rubberoid' gaskets for both the rocker-cover and the 'tin' sump---much better than the cork variety which as Peter so succintly put it "are rubbish". When fitting the rocker cover, whether it is an alloy version the original 'tin' version, I use a fibre washer, then a flat washer and finally, a nyloc nut. By using a nyloc nut, it doesn't have to be done up very tight to stay in place; the fibre washer and the 'nylon' part of the nut prevent oil travelling up the thread of the securing stud

 

[fiat500]

I always use recommend the use of the 'rubberoid' gaskets for both the rocker-cover and the 'tin' sump---much better than the cork variety which as Peter so succintly put it "are rubbish". When fitting the rocker cover, whether it is an alloy version the original 'tin' version, I use a fibre washer, then a flat washer and finally, a nyloc nut. By using a nyloc nut, it doesn't have to be done up very tight to stay in place; the fibre washer and the 'nylon' part of the nut prevent oil travelling up the thread of the securing stud

That's the original setup.
For perfectionists, the nyloc nuts (on later cars at least) had a white insert; the steel washer and the fibre washer had the same overall diameters and weren't very wide.
With a new gasket that hasn't yet "found" its position, I have sometimes used the tackiness of a thin skim of grease to locate the gasket onto the cylinder head; you could use a whisper thin coating of gasket sealant.

 

[smart51]

In reseating the rockers, I noticed that one of the push rod tube rubbers was pinched. Head off for the 3rd time, new gaskets and reassembly and the engine runs. The exhaust blows a bit from the elbow shown in the picture. The bolts are tight so I suspect the exhaust header is not straight, causing a bit of gapping. What's the best way of sealing it? The gaskets don't have much thickness to compress.

 

[fiat500]

In reseating the rockers, I noticed that one of the push rod tube rubbers was pinched. Head off for the 3rd time, new gaskets and reassembly and the engine runs. The exhaust blows a bit from the elbow shown in the picture. The bolts are tight so I suspect the exhaust header is not straight, causing a bit of gapping. What's the best way of sealing it? The gaskets don't have much thickness to compress.

View attachment 440295

If that's as far as they go when tight I assume that the cause is most likely that there is something such as a piece of broken stud thread in the bottom of the threaded hole, or some other thread damage that doesn't allow it to be fully inserted, or maybe there is insufficient depth of thread on the bolt itself or the bolt is too long.

It would be best to investigate by removing it (or the pair of them) completely. If it will still leave plenty of threaded bolt inserted, you could grind off a bit from the end. Alternatively, how about a couple of flat washers under the spring washer, in order to raise it a bit?

Worst case scenario....use an additional gasket?

You're on a hiding to nothing if you use something such as exhaust putty, unless you are able to get the elbow and exhaust flange to properly seat against each other; in which case, you shouldn't need any sealant.

 

[smart51]

This morning I took off the elbow an offered it up to the head without a gasket. It rocked side to side on the head, and on a flat surface. That's easy enough to fix on a linesher. Motobambino posted me a new set of gaskets over night so all was set up for a simple fix.

The newly flattened elbow still rocked against the head. With bolts done up finger tight, a 0.23mm feeler gauge will fit in on the fan side and a 1.13mm gauge on the thermostat side. I'm now taking a sanding block to the face of the port. The new gaskets are 1.4mm thick and the old ones 1.0, so they should take up the difference, but I'll clean up the face anyway.

 

[smart51]

And there we have it. A sealed exhaust.

 

[smart51]

Here's a question. Will my carb need rejetting because of the 35/75 cam?

I've tried to think it through but not come to any conclusions. With the valves open for longer, the air flow will be spread out more, so the pressure drop in the carb might be a fraction less. Since carburettors are non-linear, it might make it run slightly lean. But then it might not. So I thought it best to ask the wise heads on here for their previous experience. Do you think I'll need a bigger jet or not?

 

[smart51]

After a few shorter test drives, I went out to my regular speed trap. Top speed is still 60 MPH. Replacing the camshaft and timing chain made no difference in performance at all. The car is running well, so I've not broken it, but the change has achieved nothing.

 

[smart51]

In a moment of self doubt, I've checked the camshaft alignment today. With the rocker cover off, you can rotate the push rods freely with your fingers until the cam pushes them against the rocker arm. The inlet pushrod stops rotating 60° BTDC and loosens off 79° ABDC. Assuming 14.5° of ramp, it suggested the cam was set to 45/65 rather than 35/70. With 38 teeth on the cog, I guessed that it was 1 tooth out.

So I took the cover off and rotated the crank until the dot was in the right place. There was a heart-stopping moment when the other dot didn't come in to view. A deep breath later and I worked out that the dots would only align once every other rev. One turn of the crank later and the dots were in the right place. While I was at it, I bent back the retaining plates and checked the bolt torques. I worry too much.

 

[Goldnrust]

Don't forget that the 35/75 spec will be at a certain amount of cam 'lift', not the start of the ramp off the base circle.

Also measuring by checking push rods you have to take the valve clearances into account, the push rod will go 'tight' at a cam lift equal to the valve clearance. You need to take that into account and set the clearances to the lift the cam spec is measured at if you want to get close to accurate using this technique. Wit the standard 0.20 / 0.25mm clearances for the 650cc engine, that 0.05mm difference between intake and exhaust clearance will definitely make your measurements look wonky.

As long as the dots align, for a fairly stock engine I wouldn't worry too much more.

 

[fiat500]

In a moment of self doubt, I've checked the camshaft alignment today. With the rocker cover off, you can rotate the push rods freely with your fingers until the cam pushes them against the rocker arm. The inlet pushrod stops rotating 60° BTDC and loosens off 79° ABDC. Assuming 14.5° of ramp, it suggested the cam was set to 45/65 rather than 35/70. With 38 teeth on the cog, I guessed that it was 1 tooth out.

So I took the cover off and rotated the crank until the dot was in the right place. There was a heart-stopping moment when the other dot didn't come in to view. A deep breath later and I worked out that the dots would only align once every other rev. One turn of the crank later and the dots were in the right place. While I was at it, I bent back the retaining plates and checked the bolt torques. I worry too much.

View attachment 440806

You do worry too much, but if those tabs have been loose whilst youve been on shakedown with the engine....... you don't worry enough.