GTO missing sheet trouble shoot

Trouble shooting missing sheet detector,
Sheets feed fine when impression off however
when impression selected machine trips off.

My first question is does the missing sheet / mis aligned detector
only function when machine is ON Impression? Or if the sheet is mis aligned
hitting only one gripper the machine should trip off?

I detached hose going to sniffer and was able to feed sheets on impression,
so I assume I have an air leak most likely in the feed gripper assembly since I
replaced all the hoses and cleaned/inspected the sniffer piston.
If there is not an air leak in the assembly could there be too much air pressure
going to the piston? or anything else to look at?

 

Urethane tips on traveling feed grippers wear out and must be replaced and properly seated/adjusted. This is the most common cause of this problem. If the assembly is original, the coil springs wear into the tube, causing the same problem.

 

Yes the urethane tips were worn out, I replaced, I am going to replace the entire assembly (I can see grooves where spring is located).
Could you tell me if the missing sheet detector is activated when just feeding sheets thru with impression off?
thanks!

 

Never seen one wired that way. What model year and how many printing units?

 

Oops, misquote. Never saw one that only tripped off when on impression. Should read misfed either way.

 

Thanks for the response,
I went ahead and replaced whole assembly since there were
deeply worn spring grooves...did not detect leak but it was time,
press is 1981.

Despite that still having issues.

If I take strips of duct tape and cover the gripper holes really well I
can get the machine to feed when on impression.
So my grippers must not be set correctly?, not sure the proper way
to set other than I made sure with strips of paper that pressure was firm/even.

(Also if machine is on paper/run and misses a sheet the machine does not shut down)

Thanks

 

I don't recall the earlier GTOs continuing to run after a missed sheet when running on "paper only", but it does make sense. If you bought a new feed assembly from Heidelberg, it should have run without having to set the grippers, but whether new or secondhand, if you continue to have the same problem, you're going to have to square the urethane tip to the pad surface. If the urethane is not flat on pad, air will leak out and cause the sniff piston to signal a missed sheet. Also, getting the urethane tip to rest evenly from front to back on the pad said me times takes some bending of the finger.

 

Thank you I'll take a closer look at the pads squaring up, the gripper is after market with upgrade spring.

 

Atermarket...good luck with all that. Given you get it to work properly, keep it well lubed.

 

Thanks Junker, got it to work, solid advice. The fingers were grabbing just on the
edge of sheet so I took the assembly off and adjusted flat (easier to see what was going on).

 

Very good! My concern is with the Chinese assemblies eating themselves up in a short period of time, keep it well lubed and you may get long life out of it. Meaning, keep it sprayed down with aerosol grease and it may serve you well.

 

Actually sent the Chinese assembly back got a refund totally unusable, one finger off by a 1/8" height. Went back to original assembly although the groove hasn't worn thru it will probably last longer then what I purchased, least I learned a lesson next time buy original part that is critical, waste of time with the other remakes.