Jackshaft Stern Drives

[Sknzfan]

I'm looking at a 1996 Carolina Classic with twin Volvo diesels (KAMD 42s) with jackshafts and duoprops.<br /><br />During the sea trial, I noticed a severe vibration, mainly around 3000 RPMs. Surveyor told me that it was a normal condition on Carolina Classics or Albemarles with this type of drive configuration? You have to run one engine 100 turns faster or slower to avoid/eliminate the vibration he said.<br /><br />Can anyone verify that for a fact, or is there something there I should worry about?

 

[mercrewser]

Re: Jackshaft Stern Drives

The surveyor you hired to examine such an expensive boat should tell you. I would say the uv joints should be examined, as well as all sorts of other things including bearings etc.

 

[Sknzfan]

Re: Jackshaft Stern Drives

He's an accredited surveyor (SAMS) with 20+ years of experience, so I certainly have confidence in his capabilities...having said that, I always follow the creed of "trust but verify".<br /><br />Part of my uncertainity is due to my own admitted ignorance when it comes to boat repair and maintenance...I have a lot to learn!!<br /><br />To that point, what exactly is a "uv joint"?...not something I've heard the surveyor mention...yet.<br /><br />Thx for the info!

 

[mercrewser]

Re: Jackshaft Stern Drives

universal joint. I'm not quite familiar with Volvo Pentas, nor Jacksafts. Do both engines vibrate or just one? If the engines are run at different speeds the harmonics will give some vibration and a bad sound.

 

[snapperbait]

Re: Jackshaft Stern Drives

There should be no vibration at all, at anytime, period... <br /><br />I seriously doubt that high end builders like Carolina Classic or Albemarle would engineer a boat to have "normal" vibration at any speed... <br /><br />Bad/warn universal joints could be one possibility, poor engine alignment, several other possibilities too..<br /><br />I'd loose the surveyor and talk to or have a certified Volvo tech look at it... I'd also get on the phone to Carolina and Albemarle and inquire with the factorys about this vibration..

 

[Sknzfan]

Re: Jackshaft Stern Drives

Appreciate the insights...gives me a path to follow...I'll put a call into Carolina and look for a mechanic to take a look at the boat as well.<br /><br />Thanks!

 

[Capt Ken]

Re: Jackshaft Stern Drives

He's probably talking about an harmonic vibration which one might feel with both engines running the same rpms. Usually can be stopped by up'ing the rpms on one of the engines. Has nothing to do with alignment or bearings. Very common on larger boats. In fact, most of the time we use this vibration to tell when the engines are perfectly sychronized and if the tach's are correct or not. I've seen it get bad enough to rattle the deck hatches in the cockpit of a 54 Bertram.

 

[Sknzfan]

Re: Jackshaft Stern Drives

Exactly Capt Ken...when the engines were synchronized, the vibration was definitely severe enough as you say to rattle the deck hatches!...never having experienced that before, it did seem odd/troublesome to me...when we up'ed the RPMs of one of the engines, it stopped.<br /><br />For peace of mind, I should still probably have someone look at the uv joints, bearings and engine alignment as others here have recommended.<br /><br />Can someone explain to me how that is done? Does the boat have to be hauled out to do it? Who should do the inspection (i.e, Volvo mechanic?) and ballpark how much so I expect to pay for it?<br /><br />Thx!!

 

[WillyBWright]

Re: Jackshaft Stern Drives

It's strange, but oh so true. Once such a quirk is found, it always seems that's exactly where the operator absolutely "has" to run it. Slight variations just seem to be simply "out of the question" for some reason or other.<br /><br />Harmonics are a property of most any mechanical device, and multiples frequently magnify them. They can sometimes be minimized, but Physics is Physics and until somebody can change those laws, we're stuck with them.

 

[Sknzfan]

Re: Jackshaft Stern Drives

For what its worth, thought I would share the response I received from the company.<br /><br />Gentleman I spoke with stated emphatically that you should not experience that type of vibration when the engines are running synchronized - not how the come off the production line. He said it's one of two things:<br /><br />(1) Two bearings housed at the transom are bad...said simple test was to try and lift the outdrives up or down and side to side. If there was movement either way, the bearings are bad.<br /><br />(2) The jackshafts are out of balance. If the engines are removed, which one of these was for piston repair, he said 90% of the time the jackshafts aren't balanced correctly when the engine is re-installed.<br /><br />Procedure involves running the engine up to approximately 2900/3000 RPM and check for any vibration. The shaft will appear to become fuzzy as it starts to vibrate. Critical speed for this tube is approximately 2900/3000 RPM. Worst vibrations should, but not always, occur in this range. Reduce the RPM to the worst vibration to begin the procedure using weights.<br /><br />Learn something new every day!

 

[rodbolt]

Re: Jackshaft Stern Drives

dude<br /> loose the surveryor.<br /> I work on a lot of those beats here on the frigid coast.<br /> they dont vibrate.<br />the type C and E drives are bullet proof.(well almost) the bearings at the transom cannot be tested without removing the drive coupler and the upper drive housing and checking the rolling torque of the shaft. there is another set of bearings just like them at the engines. most from the factory have plugs in place of grease fittings and never get greased. the two pins that hold the fork to the transom assy can become wallowed out. the drive universals can fail. the weights can be slung off the shafts. I think they are full of bo looney about the drive couplers as the shafts are not balanced in the hull. cant and will never happen. the shafts are balanced then installed. they tried to tell me the samer horse hookey once and I asked them if I could bring the boat to edonton and allow them to do an onboard shaft balance man was that funny, anyway get this to a very competent tech and make sure they are very familiar with jackshafts. the albermarles dont use ujoints and shaft alighnment is not super critical and with the deck in place next to impossible to acommplish.CC's dont use ujoints either. both use drive savers and they work wonderfully.<br />good luck and keep posting<br /> PS make sure the props will come off before you buy it <br /> and nothing in a blue and white box is cheap.<br /> ditch that surveryor

 

[BRIAN03]

Re: Jackshaft Stern Drives

The jackshaft boats built by Albemarle and Carolina Classic use a two piece jackshaft. Its a horizonal splined assemble. The ujoint are very large joint. The KAMD42 is a diesel engine and will have different harmonic frequencys than a gas engine. If you are not used to it I will scare you. The jackshaft with the horizonal spline coupler will exaggerate the engine hormonics. If the engine are synchronized there should be little vibration. The ujoint on the drive are half the size of the ones on the jackshaft. The ujoints on the jackshaft can be greased relativity easy compared to the drive ujoints( pull the upper gear box). The best judge would be the person who ran the boat previously(the past owner/captain. If they are no help pull the jackshafts and inspect ujoints and pull upper gear box on the drive to inspect drive ujoints. Big fan of the Volvo Penta diesel and the Volvo drive.

 

[Peter J Fraser]

Re: Jackshaft Stern Drives

If you know anyone who is a competent heavy truck mechanic ask him to have a look at your drive shafts. They should be no different to what is found on any heavy big rig. Check the universals for movement, check the mount flanges for runout, check the splines in the slip yokes for wear and any radial movement which will allow the shaft to ocsillate and check that the universals at each end are correctly lined up. If the alignment is even 1 spline out, then you will get vibration particually if you have unequal angles at each end of the shafts.<br />Good luck<br /><br />Peter

 

[BRIAN03]

Re: Jackshaft Stern Drives

What does a truck mechanic have to do with boats? Everyone I ever knew hated boats and had greasy boots. I take it you dont like diesel boat mechanics. The drive-shaft in the boats Ive seen dont look like any truck drive-shafts I have ever seen. Maybe there different on the other side of the pond. Most trucks here run 3406E or Detroit 60 series. Maybe you have small trucks there. Most new over the road trucks(here) run aleast 500 plus hp. Drive-shaft size is proportional to hp.