Engine/tranny clunk only at idle when in gear

2

2003380

New Member
Apr 12, 2007
66
NY LI Sound
Boat Info
2003 380 sundancer
Engines
8.1 Gas
I have a 2003 380 Dancer with 8.1 gas engines.

On the prot engine, when at idle and the trannny is in gear, I get a clunk clunk clunk. and the engine starts jumping around. Does not do it at idle in neutral or when in gear above 900 RPM.

Mechainic thinks it is a misfire. I don't think so. He had me change idle computer, all new wires, new plugs. Had a full computer scan- all good. no help so far

Any thoughts??
 
Some one else had this problem before and I believe the cause was eventually found to be a misfire (ignition or injector, I forget which) combined with a 2 piece flywheel/damper plate. You might try searching to find the thread.
 
I had Velvet drives in a Mainship. Manual indicates they will knock if the slow idle is too low. I had a terrible knock in the port engine. thought the worst! After much research, simply raised the engine idle and the Knock went away.
I hope this is the case with you.
 
sad1 said:
I had Velvet drives in a Mainship. Manual indicates they will knock if the slow idle is too low. I had a terrible knock in the port engine. thought the worst! After much research, simply raised the engine idle and the Knock went away.
I hope this is the case with you.
Click to expand...


+1. Well documented on the WWW. From what I have read, the knock is not life threatening...it just is. Some have "not" lived with it for years by raising the RPM slightly.

HTH
 
contrary to a couple of the posts, the damper plate or dampening device is a crucial part of the driveline, its purpose is to dampen the explosion that happens on the firing stroke of any engine, an engine if broke down into laymans terms is a jackhammer, the piston approaches TDC and all of a sudden an explosion occurs and the piston has a tendency to speed up, in a v-8 it happens 4 times per revolution. at times i have seen a fail safe damper fail on a diesel engine causing metal to metal contact and the 2" input shaft snap from the torsionals.
A rattling transmission will cause pre mature wear inside the transmission, it burnells bearings, opens clutch splines. its there for a reason and if they rattle, change them. the cure isnt raisng the idle. torsionals are much more prevelant on a diesel engine because of the longer stroke and compression ratio. it is one of lfes wonders trying to cure torsionals on engine, they exist and only can bre hidden or a better term...dampened. at times a bad damper will sound like a coffee can full of marbles, sometimes like a rod knock and yes torsionals are much higer at idle because the explosion is spread farther apart and as the rpm raises the torsionals do have a tendency to dis-appate...but not go completely away
Eric
 
Last edited:
Thanks for the input !!

ZF transmission. Merc mechanic said I have the updated dampener plate.

My mechanics thinks maybe injector.

I am into this guess work for about 3K and no resolution.

Looked on web - couldn't find any info.

I wouldn't want to buy a boat that did this and I don't want to live with it.

Thanks
 
Just an FYI, but my wifes GMC(Chevy) Suburban had a miss that was picked up on the mechanics scanner/scope and was able to tell exactly which injector it was. And that is a 2001. I am sure that a good mechanic with the right tools could be able to diagnose this quickly. Your $3K and no resolution is why I try to do as much of my own work as possible. Most mechanics are making "educated" guess' as to the problem, unfortunately on your dollar. Good luck.
 
On the 8.1's you can't change the idle. The problems I see with those engines are the spark plugs going bad or the injector. Does the motor turn up the proper rpm's if not it might be only on 7 cylinders. If you have a good merc mechanic he could hook his cds to the motor and while you are running do a cylinder drop test to find the cylinder. If you still can't find it he could then do a injector flow test, and that will show you which one isn't flowing the same amount as the other injectors. Spending $3000 on trying to fix this so far is rediculous.
 
do a tune up first, I had same issue. It was a flex flate on one engine, and on the other i thought i had same issue, but mechanic was able to check it out and found carb starved for fuel after a rebuild worked like a champ. Does it stall at idle? if so more than likely tuneup, if not more than likely flex plate that is the piece between engine and transmission got a bunch of springs on it to normalize the rotation at idle speeds,
some times it is just timing/ bad carb. Hopefully it is the latter, as flex plate will run you about 1300-1500 to fix, as u have to haul engine. to replace a 200 dollar part.

If you have an email account able to accept a large file few hundred meg I have a move file that my surveyor made for me when he was surveying the boat u can clearly hear the clank clank of the flex plate
 
Last edited:
just a note, a miss will cause a torsional noise! i just got bit on the ass with this, I told the guy his damper was bad, changed it, tuned the engine, i could hear a little growl...this one got me, was at the end of the road because the engine had under 100 hours......pulled down the engine and found a piston .040 smaller causing a slap...im well seasoned, but was quite embarrassed...i still cant explain the piston, it must have skipped quality control
point being, obviously a miss in the engine would be a less expensive and easier fix...I paid for my mis-diagnosis, just make sure you dont pay for his eric
 
Engines turn up to 4600 rpm. It only happens under load at idle. gotta be between engine and tranny.

Gotta find a merc mechanic who cares about his work to solve the problem. So much for work ethic and mercruiser customer service.

Boats going in soon and the saga continues.

Thanks
 
You must log in or register to reply here.

Forum statistics

Threads
113,253
Messages
1,429,324
Members
61,129
Latest member
MinecraftRuSwilm
Back
Top