I’ve got the shakes!

sunquest

sunquest

Well-Known Member
Joined
31 Oct 2005
Messages
871
Location
Kent
Visit site
Underway the boat is getting noisier and vibrating. Checked the prop shaft to gearbox gap all within 10 thou. Cutlass bearings renewed 3 years ago BUT when in neutral tickover is fine, as it revs to 1200rpm the engine shakes/vibrates and steadies at around 2200rpm. Does this point to sagging engine mounts? The engine is a Cat 3116TA mounted on Barry pin mounts. thanks in advance. Geoff
 
Does the vibration occur in neutral or in-gear or both? If in neutral, have a look at what is happening in the engine bay. Get someone to rev the engine for you and see what's going on. It should be possible to see if the engine mount is broken. If it only occurs in-gear, the it would point to something in the transmission, shaft, prop or gearbox. Sorry if this is stating the obvious, but start with the simple things first.
 
Best to view with strobe light. Get someone to drive the boat while you go into e/room with strobe light. Then you will see the vibration in slo mo
 
Thanks for your input guys. Yes it is vibrating both in gear and neutral. In neutral as the revs rise you can visibly see the engine shake and smooth out at around 2200 revs. The engine revs smoothly without misfire or hic cup through the rev range. If it is the mounts Cat want 400 pounds each. I would probably look at R and D mounts if anyone has experience of them. Jfm, can you clarify how to use a strobe light? Ie is it connected to a 12v supply and what are you looking for at the strobe end. Incidentally I believe the mounts are original equipment fitted 23 years ago.
 
rafiki_ said:
How did you lift the engine John?
Click to expand...

Paul, hi, you don’t need to lift the engine, if you do them one at a time, and remove the base packer square section you can just about wiggle them out and get the new ones in. The only one you need a bit of lift with is the rear outboard ones as they only have a plate packer,

4068335B-D061-424F-BBDF-047C0C2CAF2D.jpg

The ones on the port engine are the replacement ones, it was as shiny as the starboard ones but I had a wee accident when I was doing an engine flush with the Radylim even though I immediately flushed it off the mount it dulled the surface instantly
 
Spare Thyme said:
Paul, hi, you don’t need to lift the engine, if you do them one at a time, and remove the base packer square section you can just about wiggle them out and get the new ones in. The only one you need a bit of lift with is the rear outboard ones as they only have a plate packer,

View attachment 71689

The ones on the port engine are the replacement ones, it was as shiny as the starboard ones but I had a wee accident when I was doing an engine flush with the Radylim even though I immediately flushed it off the mount it dulled the surface instantly
Click to expand...
Nice job John
 
Think laterally.
Rope around the prop
A damaged prop ie bent or missing part of a blade
Cutless bearing worn, delaminated or missing rubber.
Loose R&D coupling
Alignment problem
Engine mounts, sagged or sheared studs, you may need a pry bar to see
Bent shaft
Pretty much in that order of liklihood.
 
Bandit said:
Think laterally.
Rope around the prop
A damaged prop ie bent or missing part of a blade
Cutless bearing worn, delaminated or missing rubber.
Loose R&D coupling
Alignment problem
Engine mounts, sagged or sheared studs, you may need a pry bar to see
Bent shaft
Pretty much in that order of liklihood.
Click to expand...

Thanks Brandit rule out the first 3 and the bent shaft all checked recently when ashore, suspect the mounts but will check alignment and R&D coupling.
 
rafiki_ said:
You can get a 12v strobe for a car. You need it strobing at the same frequency as the engine revs. All should be clear on the strobe instructions.
Click to expand...
nope, you want one with a variable frequency that you can tune with a knob. The car ones strobe off the ignition so you can't choose your own frequency and you dont have ignition on a diesel.
You can do it with an iPhone app or get a professional beast. Critical thing is to get one with a tiny flash duration so the image is sharp and these are not cheap - I have this one. https://www.coleparmer.co.uk/i/mona...d-with-115-230-vac-recharger/8770105?pubid=WZ
 
Last edited:
Bandit said:
How did you check the shaft?
Click to expand...
if something is vibrating the strobe light let's you see it in slo mo. Tells you if shaft is bent or if there is an alignment problem. You just run the boat, turn e/room lights off and look at everything while twiddling the flash-rate knob.
 
No expert on Cats but I've just been putting together a maintenance worksheet for a C18, using the manufactures manuals and schedule. I noticed something called a crank shaft vibration damper that requires inspection every 3000 hrs - not idea if applicable to your Cat but might be worth checking and eliminating from the possibilities.
 
Bandit said:
How did you check the shaft?
Click to expand...

When the boat was ashore I used a dial indicator near the P bracket up near the entry through the hull and in between. It is a 2” shaft and the readings were minimal if I remember no more than 10 thou.
 
If it vibrates more noticeably at two points in the Rev range of the engine, one at low rpm and one at high, it’s definitely a rotational issue. Most likely an engine and shaft alignment issue, either cutlass bearing or engine mounts position to blame
 
You must log in or register to reply here.

Share this page

Top