Source of Ticking Sound Found - Loose Gear on Crankshaft

[VFR750]

I found the cause of my engine ticking sound: the cam drive gear was loose on my crankshaft.



I had a noticable ticking sound coming from my engine. I did not notice the ticking when the engine was cold, but after driving it a bit, and opening the lid with the hot engine running I could hear a distinct tick-tick-tick... sound. The ticking sound was coming from the rear, center of the engine, and changed with speed. Valves were adjusted correctly, altenator replaced, Carrera Tensioners working.

I had to teardown the engine for a blown head seal. When the crankshaft was inspected by Tom at Tom's Rennshop, the cam drive gear was found to be loose. No other problems were found with the engine.

This is a relatively rare problem (1 in 100?), but might not be in the future, as engines get older and older.

The crankshaft (with gear still attached) went to Armando @ CCR in TX for weld repair. Just got it back today. He rewelded and ground the crank, and replaced the gear with another used one. He returned the crankshaft with the old gear and key.

Looking at the gear, it is obvious the loose gear would cause the ticking sounds as the gear hammered back and forth due to cam-load feedback through the chains and intermediate gear. The key is very loose in the slot, and worn a large amount. Not shown is the face contact surface that has fretting/galling/metal transfer from the crankshaft shoulder.

BTW, I'm replacing the intermediate gear too. The teeth were pitted from the impact with the loose gear. New chains and sprokets too.

The ticking sound, and the damage caused likely affected the cam timing, but very likely less than 1-2 degress. It is also not likely the key will fail outright, but the wear will accelerate as the motion gets larger and larger.

Add it to the list of what causes ticking sounds in a flat six.

[timmy2]

Thanks for posting your find.
How many miles on the engine?
Has anyone been in there before you?
'82 3.0?

[VFR750]

Yes an 82 3.0l First time in there.
133,650 miles

[ischmitz]

sounds like you caught it in time before the big DISINTEGRATION event...
Ingo

[VFR750]

Ultimately the keyway will fail. But I think the wear, and increase in mis-timing of the cams would be more noticeable and louder.

That is why I posted. If you have a ticking sound, this might be the reason.

You might be able to detect it with the cam covers off. I had no knowledge of the issue until the crank was inspected.

[john walker's workshop]

got one of those on the shelf. i figure i can get it rewelded sometime when there are no cranks around anymore.

[KTL]

Thanks for sharing and good to see you found the source.

That woodruff key is a big honking key and the groove in the crank is quite deep. So was the play primarily in the gear? Once the gear became loose, it used the key to loosen up the crank keyway too? Just curious.


I think a lot of the DIY rebuilders would overlook the cam timing gear on the crank and just focus on the journals and machined areas where the radial seals ride. It's sort of easy to ignore that gear because its not something most people want to mess with, along with the spacer, distributor gear and precision circlip.

[VFR750]

The gear was loose on the shaft. Only Armando knows how distorted the keyway was in the shaft.

Tom and I did not remove the gear before shipping it to him. All I can see is the relative damage.

But I can say the key does not have appreciable marking from the distributor drive gear, which leads me to believe the key was not moving very much, if at all, relative to the keyway.

[VFR750]

Weld repair was a lot less expensive than finding another crank. So I went the repair route. Crankshaft is still std/std with no cracks.

got one of those on the shelf. i figure i can get it rewelded sometime when there are no cranks around anymore.