Flexable mounts with 4 in. bolt spacing?

[Roger Eaton]

I know there has been a ton of information given on selection of flexible engine mounts and the Vetus K50, with mounting hole spacing of 3 inches, seem to be the mount of choice.   My mounts have a hole spacing of 4 inches.  I would like to keep it simple and replace these mounts with ones that also have 4 inch spacing.  Any recommendations?  Thanks

[Ron Hill]

Roger : Always give your hull number and production year when you ask a question.  For this question it would be nice to know which engine you have.
I'm not too sure about your "hole spacing of 3 inches"??  The Vetus K50 and K75 mounts have a 4" center to center hole spacing of the foot brackets that hold the mount to the engine bed!!  These are the holes that the lag bolts go thru and screw into the engine bed.
Are these are the same holes that you're talking about??

[Roger Eaton]

Ron,

Thanks for your responce.  I am glad to hear that the K75 lag bolt spacing is 4 inches.  I have never held one in my hand and was only going on the dimension given in the Vetus 2006 catalog, page 127, which gives 3 inches for the spacing. Hopefully Vetus is not planning on changing to 3 inches. Shurley not.

Roger Eaton, C34, 1988, Hull 734.

[sedelange]

Roger:
You are right.  Vetus shows them at 3".  Go2Marine shows them as 3 15/16" spacing.
http://www.go2marine.com/product.do?no=77169F#desc

Steve DeLange

[Ron Hill]

Roger : I guess the catalog is a misprint.  I went out into my garage and measured one of mine and it's 4" or could be 3 15/16". 
At the present time I have K50s on the front mounts and K75s on the rear.  The slightly stiffer rear mount does eliminate the drive shaft "ticking" against the molded tube that goes thru the hull.   

[Mike Vaccaro]

New wrinkle on old subject:  We recently installed a PSS mechanical shaft seal in place of the old packing gland.  This essentially results in the loss of the bearing surface of the packing nut--now the shaft is only born by the coupling and the cutlass bearing.  We've noticed a slight increase in "shaft whipping" at low RPM (i.e., high engine vibration)--this small inertial bending is similar to a jump-rope bowing.   

We had a similar vibration at low RPM with the old gland, but it is slightly more pronounced with the new seal (i.e., loss of the third bearing surface).  We have 4 K50's installed.  Overall, we've been very please with the performance of the K50's and the Bullflex coupling and avoid the small part of the throttle band that causes irritation. 

Agree with Ron that stiffer mounts (especially the aft mounts) are a good way to go.

Cheers,

Mike

Mike

[foursailing]

Mike - Sounds like your shaft / coupling might be misaligned - causing the shaft wobble.  The extra weight of the PSS stainless donut imay be making the wobble worse.

I wouldn't consider the stuffing box to be a "bearing" surface - it's attached by a flexible hose to the shaft tube.  The only bearing surface is the cutlass.

Bill

BTW - PSS are great - had one on my pearson 30 - it will be one of first projects on my recently acquired '99 C34.  Where did you purchase your PSS?

[Mike Vaccaro]

Bill,

Got it at the local chandlery.   Wanted the old, non-vented version which is no longer produced--had to hunt a bit.  The company is now only producing what they used to call the "high speed" version with the nylon vent/water injection tube.  For sailboat applications, they recommend running a vent line from that nipple to a point well above the water line--in effect, making the bellows "self burping."  At hull speeds below 12 knots, cavitation due to motion is not likely.  Didn't want another hole below the waterline (personal choice).

Engine is currently aligned to .002 with a Vetus Bullflex coupling, so suspect slight whipping is a function of engine vibration at low RPM and the K50 mounts on the rear end.  Agree that the old nut was not a true bearing surface, but it did serve as an effective damping surface.  Overall vibration is considerably lower than stock mounts on the M-25XP, which vibrates substantially at recommended idle RPM, but smooths out almost immediately as power is advanced.  Also switched to a light-weight feathering prop; so can't be certain about interaction of all the running gear yet. 

Recommend that folks switching to Vetus engine mounts consider stiffer mounts on the aft end of the engine, per Ron's advice.  Happy with a dry bilge for the first time since we owned the boat!

Cheers,

Mike