Salam to all members hope you all are doing fine.
I need some suggestions/opinions from senior pw members regarding the problem I'm facing with my car now ,first off I'd like to tell you its a 2006 model civic Vti 46k driven with no meter reversing or anything of that sort since it has been with me from the day 1 and was used as a second car until the last 2 years, I installed cng a year before when the car had done 30,000kms on petrol, the oil I use when it was on petrol was 10-30 and switched to 10-40 with cng conversion.
Day before yesterday I was on my way back home while driving the engine suddenly dropped the rpm and the went off and started to give missing when I tried to start it , without taking any further risk I towed the car to home and the next morning when I started the car the missing was still there and there was some noise in the engine head as well, when the mechanic opened the head to check the valves after making sure all else was perfect(COILS,PLUGS,ENGINE TIMING) I was surprised when he showed me a small cut screw stuck in between the valve and head which resulted in a bent valve besides that everything else was perfect ,we found out that cut screw actually came from the cng venturi and finally after 1 year it managed to creep into the head through the air box via throttle body which was a blunder made by that cng installation guy for not using silicone to attach the venturi with the cng supply pipe instead using a cut screw ...the mechanic told me not worry as its just 1 valve which needs replacement and he took the head to lathe machine shop which he said would repair the valve seat/seal(I dont actually remember what its called but its actually the bottom part of the head with which the valve is in contact with when its closed) anyhow he took it to some famous lathe machine operator located in saddar , when he returned he showed me that place was even and smooth when I felt it from my finger and replaced that damaged valve and put the head again along with a new head gasket and a new timing belt ..the next day he started the car and adjusted its tappets all the noise from the head was gone but there is still a very minor missing on petrol and on cng both when I WOT the car while its idling, that missing comes just in between 1000-1200rpm and its very minor, comes only when I WOT suddenly and doesn't come if I pump the throttle second time until the rpm comes back to its idle position .I got the plugs replaced too but its still there although I cant feel it while driving but still its bothering me ,got the throttle body cleaned aswell and coils checked ...I showed it to another mechanic he said its very minor and will get finished with the passage of time as the valve and the valve seat or seal (whatever it is called) will take some time to get back to its original position ...
The second issue which I wanted to discuss is my mechanic said that the timing belt was a bit lose and since the car has clocked nearly 50k kms he asked me to change it and the new timing belt he put he made it as tight as possible so that it wouldnt jump or get lose in future ...although he set the timing to zero zero after changing the belt but is it the correct methodology to tighten the timing belt as tight as possible.
The last thing on which I had an argument with my mechanic too but he finally convinced me to put 20-50 grade oil which In my opinion was too thick for just a 50k km driven car as I use to put 10-40 grade from past 1 year and before that I used 10-30 ...he showed the camshaft of my engine which was scratched on it lobes but were very very minor and was hardly able to find only 3-4 of them the mechanic told me "apke cams ragra kha rahe hain" and it would increase if I continue to use the same grade oil i.e 10-40 and made me switch to 20-50 which I still think is to thick for such a low milage engine
Here I need some expert advice from senior members who have had experienced this sort of problem and what should I do with the missing thats bothering me and will it get finished with the passage of time or will it increase just in case the valve seat/seal is not faced evenly by the lathe machine guy(thats just my wild thought),second is should it go get the timing belt and cars timing checked although the timing must be okay as he set it in front of me but the timing belt he installed was just too tight ,lastly should I switch back to the normal 10-40grade oil I use before or stick to the 20-50