Valve problems on my 3.2 engine

Hello everybody I have a problem with my 91 3.2 xj 40 engine it runs on lpg and has special valves from the beginning It has almost 300000 km and runs well no oil consumption oil pressure is over 4 bar en at 3000 rpm 4.6 bar Temperature is always perfect no leaks and no noises when its warm The compression in the cilinders when warm is between 11.5 and 12 bar With every cold start I hear a rattling noise like a diesel and when I puch it over 2000 rpm the rattling stops immediatly and it runs perfectly It starts on petrol and switches to gas and the noise is always there I think that there are valves that stay open and close after giving extra revs ore broken springs But I cannot understand that the noise immediatly stops and afterwards it runs perfectly with full power Thanks for your advices before I start dismantelling the cilinderhead

Timing chain?
12-61 Rattle After Start.pdf (42.3 KB)

Very well possible The oil pressure is good but the tensioner maybe worn thanks for the tip It was also one of my options But now I am pretty shure Thanks for the tip

These are an interference engine, if a valve was staying open then you would not have good compressions and full power would be gone.

That was also my conclusion I am convinced now that my problem is the upper chain tensioner The problem is discribed already many times , wich I did not now yet There are 2 rubber seals inside the 2 pistons Can it be enough to renew them to solve the problem are is it a new set ? I am a little bit obsest with the simplest and best fix without breaking the bank , but I try to fix wat is neccesary Any suggestions ? You can put in a complete revisioned engine and that is always the best but I want to solve this specifique problem I am gone try this first because it is simpel and let you now the result