Are Valves And Pistons Okay After Driver's Camshaft Skipped Several Teeth?

[StangGrin]

So...if the driver's side timing chain tensioner is removed without locking the cam I learned that the cam will rotate and skip several teeth. Of course this all happened so quick I couldn't tell which way the cam rotated.


My big worry now is are the valves and pistons okay. Of course the crankshaft wasn't in the safe position (keyway at 9 o'clock) when this happened, it was at about 7 o'clock.

I read where one guy had this happen with his keyway at 4 o'clock and everything turned out okay.



So is there a way I can check that the valves and pistons are okay (besides pulling the head)?


I look forward to any help you guys can offer.
Thanks!

 

[DeepList]

Did you already put everything back together after this happened, or is it still apart?

 

[StangGrin]

Did you already put everything back together after this happened, or is it still apart?

Hi DeepList,

A bit of both. It's still all apart EXCEPT I "reloaded" the tensioner and installed it. My thinking was by putting the tensioner back in it might prevent anymore teeth skipping. I haven't moved anything.

 

[DeepList]

I believe all you'd have to do in this case is set the crankshaft to "safe mode" and then turn the cam back to where it should be. Try cranking it a few revolutions, slowly, and make sure there's no interference.

 

[FrankenStang]

I know when I did it on a motor teardown when the cam spun it bent a valve.same excact thing happened to me

 

[StangGrin]

Thanks for the quick replies guys. Of course now I have even more questions.

I believe all you'd have to do in this case is set the crankshaft to "safe mode" and then turn the cam back to where it should be. Try cranking it a few revolutions, slowly, and make sure there's no interference.

DeepList - Which way would be safest to turn the crank (CW or CCW)? What should be done with the cam and the timing chain? I worry if I remove the chain the cam will shift more and make damage even more likely.

I know when I did it on a motor teardown when the cam spun it bent a valve.same excact thing happened to me

FrankenStang - How did you know you vent a valve? Did you have to pull the head? How was the piston?

 

[DeepList]

Which way would be safest to turn the crank (CW or CCW)? What should be done with the cam and the timing chain? I worry if I remove the chain the cam will shift more and make damage even more likely.

Turn the crank with the rotation of the engine. Once you have the keyway on the crank in safemode, then all the pistons are below deck and you can put the cam back to where it should be. Then set the timing mark on the crankshaft to 6 o'clock. Make sure the timing marks on the chain are lined up. Turn the crank a few revolutions and verify nothing is interfering. I'd say the odds that you've damaged anything are pretty slim. Everything should be fine.

 

[StangGrin]

Turn the crank with the rotation of the engine. Once you have the keyway on the crank in safemode, then all the pistons are below deck and you can put the cam back to where it should be. Then set the timing mark on the crankshaft to 6 o'clock. Make sure the timing marks on the chain are lined up. Turn the crank a few revolutions and verify nothing is interfering. I'd say the odds that you've damaged anything are pretty slim. Everything should be fine.

Well that's all rather encouraging - thanks.
Another (silly) question, though... "with the rotation of the engine" is clockwise as I look at the front of the engine -right? If so, then that isn't very far to go to "safe".

 

[DeepList]

"with the rotation of the engine" is clockwise as I look at the front of the engine -right? If so, then that isn't very far to go to "safe".

Correct.

 

[duff daddy]

OH MY LORD... this safe mode shit has got to stop.....

take the followers out and you will NEVER have to worry about the cam spinning and possibly having ptv contact. This safe mode shit is stupid its useless and its lazy. Pull the followers out, and go from there. I have degreed several motors and havent had an issue yet.


If you want to check to see if you bent a valve, remove all followers and do a compression test, this will tell you if a valve is not seating correctly.

 

[StangGrin]

...take the followers out and you will NEVER have to worry about the cam spinning and possibly having ptv contact. This safe mode shit is stupid its useless and its lazy. Pull the followers out, and go from there. I have degreed several motors and havent had an issue yet.

If you want to check to see if you bent a valve, remove all followers and do a compression test, this will tell you if a valve is not seating correctly.

Ahhhh...thanks! Since the engine is out I can just do a leak-down instead of a compression check. I like the sounds of that a lot more than pulling the head just to check the valves.

 

[FrankenStang]

Thanks for the quick replies guys. Of course now I have even more questions.



DeepList - Which way would be safest to turn the crank (CW or CCW)? What should be done with the cam and the timing chain? I worry if I remove the chain the cam will shift more and make damage even more likely.



FrankenStang - How did you know you vent a valve? Did you have to pull the head? How was the piston?

yes I pulled the head, the pistion had no visable sign of where it hit but I knew and could hear that sucker hit it when the cam spun.

 

[duff daddy]

Look at my thread on how to replace valve seals, you will see a basic example of the process to remove the followers and whats needed.

 

[StangGrin]

Well...I checked the piston positions and looked at where the cam lobes are at. All looks pretty safe except I'm not sure about #4. It's piston is pretty much at the top and its exhaust valve is working on closing.

This pic is from the back of the engine looking at the passenger side cam shaft...exhaust lobe for #4. Do you think the cam has rotated enough to not cause a problem or really hard to tell?

The plan is still to find a spring compression tool to remove the followers and do a leak-down test...and resynch cams and crank.

 

[duff daddy]

Its hard to tell, you can get a video scope for under 50 bucks at harbor freight.... that would be a great tool to invest in... I think jegs and summit have a simillar one for same price also.

When you retime the motor are you going to degree the cams or just put them in straight up?

 

[StangGrin]

When you retime the motor are you going to degree the cams or just put them in straight up?

I'm just going to put them in straight up. I'm not sure what degreeing them would do for me, considering the engine is rather stock and I'm at altitude (Denver - 5280'). Also, with stock cams and cam gears how would I degree it -set the timing chain off by 1 tooth?

 

[duff daddy]

Degreeing a motor will benefit everyone !!!! From factory your cams can be several degrees off either advanced or retarded. With stock cam gears, you can grind small mounts off the keyway and that "clearance" will give you your adjustment from the keyway edges. You can also use (i have used them on a 4v motor a few months ago) the cloeys adjustable cam gears and tfs crank gear, with pre set timing adjustments.

That last motor I did we found the cams were off +2* on left bank intake and +1* left bank, and slightly more on the right.

 

[StangGrin]

Okay...I get that...thanks.
So what kind of improvements did you see after correcting the timing on that last engine? Also, what do the TFS crank gears do for ya (since they're not adjustable)?

 

[duff daddy]

see how they have multiple key-ways, keeping the same "dot to dot" but adjusting the key-way used to line up to the crank shaft will give you a range of 8*advanced or 8* retarded

 

[StangGrin]

Got it. So what about the performance results on that last engine you degreed?