Novice question : Knocking sound once on reverse, temp above 80 and car not moving

[timpurister]

Hey

I am puzzled with a knocking voice coming from the front of the engine. It only comes when the engine is in operating temperature, car is not moving and reverse is engaged. Once the car moves, no sound. I put a short video on youtube

The transmission works absolutely flawlessly, I have checked the transmission fluid ( using Redline D4 atf), and the engine works normally. So far I can think of two possible causes for this sound.
1. I just had my exhaust replaced from manifold to the rear end . Once I put the R on, engine moves a bit and something hits the block and causes this sound. If this would be the case, why it is not making any noise once I am backing.
2. I had my car on a lifter. Stopped the engine on P, then changed to N. Did my my time on the lifter, put the car on the floor and started the engine on N.

I really can not locate the source of the knocking sound. Am I in the deepest s**t of all times or am I just missing something.

Thanks already

Timo

 

[gsxr]

How many seconds does it take for reverse to engage? How many km's/miles on the transmission, and has it ever been rebuilt?

I hope that isn't the sound of the reverse piston touching things it shouldn't.

 

[JC220]

Hey

1. I just had my exhaust replaced from manifold to the rear end . Once I put the R on, engine moves a bit and something hits the block and causes this sound. If this would be the case, why it is not making any noise once I am backing.

This is the first big clue. Perhaps there was a heat shield or similar disturbed or incorrectly fitted. Or the exhaust is incorrectly fitted.

Meaning that with the torque of the engine and maybe aging engine mounts you get a rattle of some part of the exhaust hitting the body or a heat shield.

On that note have you any records of the engine and transmission mount being replaced? Do check them out also. Having noises or vibration occur at standstill in D or R and not in P or N is the torque making the engine shift.

 

[timpurister]

Thanks. The tranmission was changed at 165tkm, currently 270 on the clock. Transmission mount was replaced at 244 but engine mounts are on my to-do list.

 

[timpurister]

Just a brief update. My techie and I started a "water pump - radiator - all hoses" project on Friday and to also study noise coming from the front. I was able to hear it also once on D and even once driving the car. The root cause has to be that at least one of the timing chain slide rails had been broken and one piece of plastic was nicely stucked just below left valve cover - other pieces were on valve cover. My current thinking is that all slide rails need to changed, chain + tensioner too so it is going to be a bigger project. I knew I was on extended time with 270kmi on the clock and everything original except upper rail guides that were replaced in 2018.

I saw Joe that you recommended Febi chain kit. I actually already ordered a Swag one, want to see if the chain is really a IWIS chain. I was also planning to buy a "full engine gasket kit" from Elring and replace all the stuff possible when removing the engine.

 

[gerryvz]

No question that more than a few folks on this forum are rolling around with at least one timing chain rail broken, and not even knowing it. From my Top-End Refirb job last year, I discovered one in my car with only 142K miles on the clock, and impeccable maintenance. It happens, and many folks don't even know it. I'm glad you found (hopefully) the cause of the problem.

It's not the funnest job to replace them, and also a good time to check the cam solenoids and cam seals for leaking oil (and repair if needed). Again, other problems that many here on the forum don't even know they have.

 

[emerydc8]

@gerryvz If you had to do the top-end over, would you pull the engine out?

 

[gerryvz]

@gerryvz If you had to do the top-end over, would you pull the engine out?

Probably, yes. Because it would have allowed me to clean the entire engine as well as the engine bay, and replace more things. But for what I did, it wasn’t technically necessary.

I wonder if @Jlaa will pull his engine when he does his refresh?

 

[JC220]

I plan on pulling the engine in my 500E and doing a full nut and bolt cosmetic restoration and reseal on it + trans. Pull the heads and have them vapour blasted and reconditioned by machine shop etc. All bolts re-plated, valve covers re powder coated all that good stuff like I did on my S500 m119.

I have photos of a NOS M119 engine of the era I am going to make it factory exacting & correct restoration also on my 500E. For example if bolts were silver plated they will be re- silver plated. If a bracket was black paint I will blast, plate and paint it.

Then also drop rear subframe and galv, re Bush etc. New LSD guts to fit. Basically taking care of ALL old rubber parts on the chassis and completing the restoration of my 500E.

Will begin this next year all being well - need some other projects back on road first as priority since there is nothing actually wrong with my 500E at all and the engine compartment is already clean enough to eat your dinner off in reality.

I want to carry out this work soon for fear of NLA hitting gaskets and so forth from dealer.

 

[emerydc8]

Almost makes me want to buy an M119 engine and stand to rebuild inside the house. Though I don’t think I could get it through the front door after I finished.

 

[timpurister]

Well, a small update. One guide was totally broke, alot of stuff in the oil pump filter. I will get the heads done, tranny is getting resealed, considering to renew gears at cams but they are a bit pricey. Lets see, maybe I just close my eyes and push the "order"-button.
Only thing I can share is that everyone should open the oil pan every once in a while. I was lucky, could have gone the other way.