Compression failure

[Mat]

Can anyone assist? I have just rebuilt and reinstalled my 1.3s Fulvia engine (1974 ). With much excitement, I tried to start it and have found no compression on No. 4 - absolutely none!!) . I have used new rings etc. The valves do not appear to be sticking and feeding an airline through the chamber does result in air coming out of the choke valve on the carbs (Solex). All other 3 chambers have a good reading.
Any guidance would be appreciated, before I sink into depression. Thanks.

[John Simister]

The inlet valve can't be closing fully if air is blown out through the carb. Is there a clearance between it and the rocker at the top of the compression stroke, ie TDC with that cylinder 'firing'? As I'm sure you know, both inlet and exhaust valve clearances for a given cylinder should be set when that cylinder's piston is at TDC firing. The old 'rule of nine' doesn't apply to this engine (that is, adjust valve one when eight is fully open etc).

Otherwise it might be a damaged valve or valve seat, but you would have noticed that when rebuilding the engine.

Good luck!

John

[Huib Geurink]

I agree with John. The inlet valve does not close. Either insufficient clearance or damaged valve / seat or mis aligned guide.

[mat]

John/Huib
many thanks. I am resigned to removing the head! I have checked clearances and widened the gap at TDC, but no joy. I am obviously losing my sight not to have noticed something amiss, or just lost in the anticipation of rebuilding. I will update
regards, mat

[Huib Geurink]

I look forward to hearing the solution. Often it is not posted on the forum. Great if you do!

[mat]

Just an update - it looks like a bent valve, which is a shame as I had sent the head away for skimming and reseating the valves (albeit this was along time ago!). I have yet to remove the valve as a normal compressor doesn't work. Perhaps carving a pretty wooden insert for the chamber will assist!

On another note, looking at the piston crowns, it looks like the valve recesses are slightly different sizes. Is this for the variation in valve size or just my eyesight? If they are different, I have also got two pistons the wrong way round!

mat

[John Simister]

Your pistons are the right way round. Otherwise their top faces would not be level with the top face of the block, given that the tops of the pistons are angled to reconcile the cylinder banks' vee angle with the flat top of the block. So no need to worry there. Glad you've discovered the cause of the compression leak, but how did the valve get bent?

Good luck, John

[Huib Geurink]

As John says, the crowns of the pistons are under an angle because of the V. They can never be the wrong way around.

The valve probably got bent during assembly. Something like bolting the head down or mounting the rockers with the tappet screws not fully retracted and the cams and piston in the wrong position.

Probably not because of a timing error. All 4 valves would have bent.

[mat]

Many thanks to you all.

Indeed it is a bent valve. Its bent very close to the 'dish' of the valve, but the lip looks fine. I guess its my fault when assembling the head, much as I would love to blame someone else!
I have a spare, so not so bad, but will have to seek a new set to run on unleaded in due course

regards
mat

[Huib Geurink]

The original valves and seats turn out to be good enough for unleaded on all Fulvia's I know. Many of the aftermarket valves burn. Does not matter whether you use leaded, unleaded or LRP. For exactly that reason I have the austenitic valves made.