3tnv76 Loud clicking after head gasket change

[Teodorpenev99]

l've a Yanmar Vio25 with 3TNV76 which was brand new 300 hours ago. Recently the previous owner overheated it due to cracked heater and ran out of coolant.


It ran quietly before I did the rebuild, the problem was compression in the coolant system. I opened it and the head was cracked, so 1 put the old head from the previous engine which had been to a machine shop for a full rebuild, also a new head gasket. Set all the valves to .020mm


Now the machine is working and firing right up, but it is KNOCKING.


l've checked injectors by disconnecting them one by one and it doesn't go away. Also tried shutting it off at high RPM and the sound is still there when the engine is decelerating even though it has no fuel when I shut it off.


It just clicks when the exhaust valve goes down on cylinder


3. I tried spinning it without fuel just with the starter and it still clicks. Even removed the valve rods on this cylinder and still the same.


What is the possible cause of this? Maybe something fell off near the camshaft which is inside the block or camshaft worn out due to the stuck overheated valve drums?


Any help would be appreciated!

 

[DieselDustRay]

My first guess would be the camshaft lobe or the cam follower on that cylinder. When an engine gets cooked like that, the cam lobes can get scored or worn pretty badly, and a damaged follower will make exactly that kind of clicking sound even with no fuel and no valve rods in the way.
Had something similar happen on a small Kubota diesel. Kept chasing the top end and couldn't find anything. Finally pulled the side cover and found a cam follower that was worn almost flat. Replaced the follower and the cam, and the noise was completely gone. So I'd maybe pull the side cover and take a good look at that camshaft and the follower on cylinder 3. Check for any scoring, flat spots, or anything that looks out of place. If the previous owner ran it dry and hot, that area takes a beating.

 

[Teodorpenev99]

My first guess would be the camshaft lobe or the cam follower on that cylinder. When an engine gets cooked like that, the cam lobes can get scored or worn pretty badly, and a damaged follower will make exactly that kind of clicking sound even with no fuel and no valve rods in the way.
Had something similar happen on a small Kubota diesel. Kept chasing the top end and couldn't find anything. Finally pulled the side cover and found a cam follower that was worn almost flat. Replaced the follower and the cam, and the noise was completely gone. So I'd maybe pull the side cover and take a good look at that camshaft and the follower on cylinder 3. Check for any scoring, flat spots, or anything that looks out of place. If the previous owner ran it dry and hot, that area takes a beating.

My next target is opening the side cover and looking what’s inside. In the next sunny days I will open it and keep you updated. The cam rods and drums were purple with vertical scarring on the side due to the heat, so I sanded them a little with 2000 sand paper. So I guess my problem is something around the camshaft.
Cheers!

 

[rbarger]

My next target is opening the side cover and looking what’s inside. In the next sunny days I will open it and keep you updated. The cam rods and drums were purple with vertical scarring on the side due to the heat, so I sanded them a little with 2000 sand paper. So I guess my problem is something around the camshaft.
Cheers!

Does this engine have the small caps that sit on top of the valve stems like some Yanmars do. If so maybe dropped one at install. Just a thought.

 

[Teodorpenev99]

Does this engine have the small caps that sit on top of the valve stems like some Yanmars do. If so maybe dropped one at install. Just a thought.

Yes, it has, but they were all where they are supposed to be. I got the camshaft out, with the reverse hammer. It has a nice colour, deep purple
My theory is that the noise was still there when I bought this machine, but the valves were loose and noisy, so I couldn’t hear it clearly and separate it from the valves noise. I think due to the overheating the camshaft expanded too much and now it is not straight at the center, so the bearings spots on the cam are screwed. I tried putting the old cam in this engine and it fits perfectly, so I guess I will go with that one. The interesting thing is that I saw only one bearing that looks like the normal camshaft bearings. I checked for a rebuild kit and it has only one round bearing in it.
I guess the other 3 bearings are just on the block walls?

What are your theories about this situation?

 

[Teodorpenev99]

I got it all assembled with the other camshaft and bearing, it still sounds the same. I have the old engine, so I will use this one until it dies completely and then see whats inside.

 

[Teodorpenev99]

The last thing that could be noisy is a piston pin or the first bearing on the camshaft. I will use it as it is until the end of the summer, if it doesn’t put a whole on the block . To check these things I will have to remove the engine. If I remove it, I will use the spare one and check what happened with this one. I will keep you guys updated when I have information. Thank you for the responses.