MAN R6 800's 38 Cabo

[HeavyDuty-Systems]

I just purchased a 2008 Cabo 38 with R6 800’s. There’s an obnoxious amount of vibration at idle throughout the entire boat, Even when it’s warmed up.. as well as troll mode. when I put the rexroth in throttle only mode, as soon at hits 800 rpms, they smooth out like a sewing machine. You barley know they’re running. The isolators are MAN and for the correct weight of the engine. Does MAN cut out a cylinder at idle and turn all injectors on at 800 rpm +? Anyone with a 38 or 40 with this power have the same vibration?

 

[Captain Ralph]

Look over those 13 year old mounts very carefully. They may have settled and not isolating vibrations.
Check the shaft log height also.
The MAN R6s are very smooth engines. I do not believe they cut out cylinders at idle.
Was this vibration noted on the engine survey?

 

[HeavyDuty-Systems]

Good point. I will certainly check the isos closer. The vibration was noted as normal. I’m Not sure what you mean by the shaft log height and how that plays into vibration at idle.

 

[Captain Ralph]

Good point. I will certainly check the isos closer. The vibration was noted as normal. I’m Not sure what you mean by the shaft log height and how that plays into vibration at idle.

As the mounts settle, the shafts get a lil lower in the logs also.
Pending your log gland type, you may see the log hose tilting down and find the shaft just touching (dancing with vibration) on the log tube, forwarding a read hard vibration into the boat.
Yes, it happens.
Putting in gear and applying torque to the engine, may rock it over a little and the shaft does not dance on the shaft tube bottom.
Yes, this happens also.

Pending the mount, some of the mounts have a height reference built in. Others may need the mfg spec to check height.

vibration was noted as normal
Noted by a real MAN rep?

Did the supposed MAN rep measure the mount heights? They don't usually but if the vibration was questioned during survey, he may have checked.

Of course, I'm not there and just throwing ideas at you. It could be just normal and you need to just go fishing.

What part of the world are you in?

 

[HeavyDuty-Systems]

Just a quick update. I emailed Sound Down, (Distributor for Rubber Design Mounts). They actually had some old data showing the model TT2 isolator model at Durometer of 70, "which I have" was too soft when paired with the R6 Engine which caused excessive vibration at idle. They switched to a durometer of "75". I ordered and received 8 of these. Engines are currently blocked up and getting switched out to the 75's. I will update this thread after a sea trial in late May.

 

[drburke]

Super great of you to follow up on the forum! This is why it works...many thanks!

DAN

 

[Hat52MY]

Another possible contributing factor, is the engine is running in "half" mode? I have 8v92's electronically controlled and just recently learned the engine runs in half mode at low RPM. In my case half mode, is half of the V (4 cylinders) as it was explained to me. It does sound a little odd with additional vibration until its bumped up to about 700rpm, exits half mode, and enters full mode on all 8 cylinders.

 

[HeavyDuty-Systems]

TT2 / 75 Isolators installed and made a major improvement with vibration.

 

[RXTSEA]

I have this same issue with the exact boat and engines. When you say "improvement" does it mean the vibration is gone or just better?