I have just replaced the cam box gasket ( used silicone actually ) on my Uno, all back together but it wont start - just get a bit of "pop" so obviously I have got the timing wrong - how do I work backwards from here to fix the problem?
Bruce

what engine have you got? what have you removed/re-fitted to do the job?

welcome to the forum

Uno 70, 1300. Removed timing belt and cam.

Ah - from memory I think that engine is timed on No.4 rather than No.1. That is, when the engine crankshaft is at TDC (notch on flywheel aligns with 0 line on bellhousing), and the camshaft pulley notch lines up with 'triangle' pointer on the backing plate of the cambelt cover, the distributor rotor arm should be pointing to the contact for the spark plug lead of cylinder number four. Not number one as for other engines...

After changing the cambelt, you usually have to remove the distributor and reinstall it with the rotor arm set to No.4, because the auxiliary pulley (that drives the distributor and oil pump) is usually bumped/moved during the fitting of the belt.

If you happen to live in Hamilton, I'll happily come and take a look

-Alex

Jenkinsb said:

I have just replaced the cam box gasket ( used silicone actually ) on my Uno, all back together but it wont start
Bruce

Click to expand...

Not sure from your post whether you replaced the gasket and used silicone or just used silicone?

If you just used silicone, did you adjust the valve shims?

I doubt you'd get shims thin enough for use without the gasket so some, or all, valves could be permanently open.

Davren said:

I doubt you'd get shims thin enough for use without the gasket so some, or all, valves could be permanently open.

Click to expand...

Interesting but I have assembled these engines without the gasket before (I use Loctite Master Gasket 518 rather than silicone) and because that gasket between cylinder head and cambox is literally paper-thin, it makes very little difference. Valve clearances are officially 0.40 and 0.45 and the paper gasket makes maybe 0.1mm difference, so clearances would become 0.30/0.35 which is still sufficient in my opinion (the earlier 128 engines ran those tighter clearances).

The shims are available from 2.70 all the way to 4.70 with most of the shims in use being in the 3-4mm range. Around the time of the Uno engine, FIAT deleted all the shims between 0.05mm increments (that is, you can now only get shims in 0.05mm increments, but there are still old stocks around). Also, lending credence to what you are saying, I think at this time the minimum shim thickness increased from 2.70 to 3.20 mm. This could have something to do with how I've seen the later wide-lobe cams worn by the edges of the buckets.

Here in NZ, engine shops just grind the tops of the valves anyway...

-Alex

Another way to check which piston is nr1, is if you set everything on the timing marks (like alex explained), and then just checking which of the cam lobes is in the air. Both of the lobes MUST be pointing upward, it then means that the cylinder is making compression and should be firing. Check your ignition leads and adjust the distributor until it sparks, or use a spare plug on the ignition lead of nr1 cylinder.. Btw, firing order is 1-3-4-2..
If everything is thightend and safe, you can start cranking the engine. Remember to adjust the distributor in small movements.

I've made the mitstake of switching nr1 piston with nr4, resulting in my eyebrows getting burned.

Hope it helps!!!