Vibration at 1000+ rpm out of gear

[Bill Allen]

I seem to have a vibration around 1000 rpm both in and out of gear, any sugestions where to look first? Starboard engine, nothing else seems abnormal. Thanks Bill

 

[Bob Bradley]

Any loss of top rpm? I recently had a bad injector, and with one cyl not firing, had a noticable vibration around 1000. I was also losing 200 or so top rpm under load (no loss of top rpm at the dock).

 

[Bill Allen]

Short of pulling them whats the best way to check? Thanks Bill

 

[Will]

There is an old DD tech's trick I've used on 6-71s. Pull the valve cover and with the engine idling, push down the injector plunger with a big screwdriver (you really have to push hard) on each injector, one at a time. If you fail to hear a change in engine operation, that is your bad injector. I've done it on 2 valve heads but never tried it on a 4 valve engine. This is like shorting out sparkplugs with a screw driver in the old days when I knew how to work on cars.
Will

 

[saltshaker]

There is an old DD tech's trick I've used on 6-71s. Pull the valve cover and with the engine idling, push down the injector plunger with a big screwdriver (you really have to push hard) on each injector, one at a time. If you fail to hear a change in engine operation, that is your bad injector. I've done it on 2 valve heads but never tried it on a 4 valve engine. This is like shorting out sparkplugs with a screw driver in the old days when I knew how to work on cars.
Will

That works great for finding a dead cylinder or injector. If he has one that has a bad spray pattern, shorting at idle may not help. It is a good place to start if you don't want to pull them out and test them.

 

[Bill Allen]

Starts instanly, no smoke idles from the get go, just that vibration as the rpm reach around 1000. It's a 6-71 J&T natural (310 hp). Thanks Bill

 

[Avenger]

Then for the test to have any value you're going to have to "short" them out at 1000 RPM. I wouldn't want to be leaning on a shaky Detroit trying to compress an injector spring with a screwdriver that's trying to skate off into the monkey-motion.

If you've got some finesse you can use a big screwdriver or pry-bar to side load the injector follower to keep it from returning. Just don't overdo it and watch what you're prying against.

 

[Bob Bradley]

Have you lost any top rpm under load? A bad injector is more likely to show itself that way. If you can't hit your top rpm, then you can start looking at individual injectors.

 

[Will]

How about a bad viration damper?
Will

 

[Bill Allen]

Be at the boat over the weekend and do a good crawl around, mounts, dampner etc. Next will be the injectors. Bill