Engine/Drive Train Noise

[dinkum1]

We recently purchased a 1975 Bristol 27' with an Atomic Four. During
our initial cruise we noticed that at RPMs above 600 there was a
knocking sound. This sound is not heard with the engine running in
neutral or increasing the RPMs while in neutral. With the engine in
forward gear and upon acceleration (more than 600rpms) the knocking
sound becomes apparent and increases as the rpms are increased.

Question: Does anyone know if this is normal for the Atomic Four or
Bristol 27 or if there might be a particular problem that needs to be
addressed? Any input or help would be appreciated. Thanks.

Michelle and Harley

[jhwelch]

Ginen the fact that the noise only happens when the shaft is turning
I'd suspect an issue with the propeller or shaft. Did you see the
boat out of the water before you bought it and did you grab the
propeller and try to move it around to see if the cutlass bearing
was worn? The shaft could be a bit out of true. Does the same
kind of noise happen in reverse?

I own a Bristol 29.

-jonathan

[dinkum1]

Engine/Drive Train Noise

First thank you for your kind reply. We did not check the boat out of the water before purchase, but we have a diver who was familiar with the boat, clean the bottom. The diver has regularly maintained the boat for several years. We specifically inquired about the condition of the prop and asked him if there was any movement in the cutless bearing. He related that because the prop is fitted so close the hull, that there was no cutless bearing. We don't know if he meant there was no cutless bearing outside of the hull or that the cutless bearing was located somewhere inside the hull and he had no way of checking it. Do you know where the cutless bearing in a Bristol 27' is located?

The diver indicated that he could not detect any movement in the shaft. Within the past week, he installed a new zinc on the prop shaft. We feel if there had been any abnormal movement in the shaft he would have noticed while installing the new zinc and reported same to us. The noise does not happen in reverse, but only in forward and above 600 rpms which is essentially our idling speed.

The noise seems to be coming from below the cockpit floor and the noise is not present when accelerating the engine out of gear.

[jhwelch]

The cutlass bearing is a brass tube with rubber splines that fits in
the stern tube, where the shaft goes through the hull. My shaft is
pretty short, so yours must be as well, since we have almost identical
boats. Once I did have a problem with the tube rotating in the
fiberglass that made a noise.

More recently, after having my engine out, I had a kind of knocking
noise and fixed it by aligning the engine better than I had when
the engine first went back into the boat.

With the engine in forwards can you see any unusual vibration
behind the engine where the shaft goes into the stuffing box? When
my engine was out of alignment I could see some movement in that
area. It might be a bit of a job to take out the 3 bolts that hold
the coupling to the engine output plate and push the coupling back
an eighth of an inch to check on alignment. Other than that, I'm
at a bit of a loss; perhaps someone else can give other suggestions.

I'd also be curious to see the boat out of the water -- is the propeller
just hitting something as it turns in forwards? In reverse it might pull
back just a tad and not have that trouble.

-jonathan

[dinkum1]

Engine/Drive Train Noise

Dear Jonathan -

Thank you again for your input. We looked at the schematics of the B-29 which I believe you own. The layout is indeed very similar to the B-27. Could you tell us on your boat how you access the area behind the engine where the shaft is located.

Thanks again,

Michelle and Harley

[jhwelch]

Being tall and having long arms makes it possible for me to get at
the back of my engine.

I take the top half of the engine cover/steps off, lay down some
folded up towels for knee pads, kneel in front of the engine and
crouch over the top of it, jamming my head between the engine
and the underside of the fuel tank. From that position I can reach
back and feel around the coupling and stuffing box area. Take a look at:

http://www.amherst.edu/%7Ejhwelch/photos/200611/photos.html

Another approach would be to blast the area around the spark plugs
to clear out dirt and grit, remove them, and lay down some kind of pad
to lay on.

A long-handled flashlight is also helpful, and even better is a work
light if you have 120v power available.

-jonathan

[minx27]

Inquiry re stuffing box for Bristol 27

Hi A4/B-27 Colleagues:
Since this is a sort of prop shaft -related thread, I would like to know your thoughts on repacking the stuffing box for the Bristol 27 through-hull/ prop shaft. What type of material do you recommend? I see that West Marine carries several products some of which contain PTFE. Any tips re this repair procedure gratefully received! (We are getting ready to attempt this soon.)
Thanks,
Minx27

PS Anyone know where to put a zinc anode on the Bristol 27? There is no exterior cutlass bearing and there is no place to attach one on the small ( but fierce!) propellor. This is something I would really like to know!
M27

[jhwelch]

I did mine a year ago when I had my engine out. The job is simple if you
pull your shaft out but very difficult if you do it in place. Before you
start to pull out your hair in frustration do you really need to perform this
job? You only need to do it if the shaft is leaking and you can't
tighten down the packing nut any more.

If your boat is like mine (and many others) the packing nut will have a
lock nut behind it. I've found it easier to back off on the packing nut
as it's closer and there's more metal to get a wrench on. I use a vice-grip
opened almost to its maximum abilities. If your nut is really stuck and you
have some space you can "start" it with a hammer; the sharp blow will
jar it loose. I used teflon-impregnated material.

In an earlier posting you said a diver had installed a zinc. I use a
collar type, which is about in inch thick and thus is able to fit on the
shaft just behind where it comes through the hull. Where are you
located? Is your boat out of the water for the winter?

-jonathan

[Don Moyer]

I'm attaching a pdf file of the procedure that I went through when repacking our own stuffing box some years ago in case it helps you, and I'm hoping another Bristol 27 owner will check in with advice on where to locate your zinc.

Don

[dinkum1]

Regarding Zinc

Dear Minx27:

We had the same problem about a month ago. After some research and posting to the Bristol forum on Yahoo, we were to get enough information to pass on to our diver.

The zinc is located on the shaft behind the propeller. The Bristol 27 shaft is 7/8" in diameter. The zincs are available at West Marine a 7/8" shaft size zinc has a 1" length. Our diver was able to put this on without any problem. Also, the previous owner advised us that this was the correct placement and size zinc for the Bristol 27 as he had replaced several over his 7 years ownership of the boat. Originally, our diver tried to install a 1" shaft zinc which is 1-1/4" in length and would not fit lengthwise in the space on the shaft. Our diver's mistake in misjudging the size of the shaft.

Hope this helps.

Harley and Michelle

[minx27]

Thank you for your responses re B27 stuffing box

Dear Don, Harley & Michelle, Jonathan & Co:
Thank you for your responses to my questions about the stuffing box and the zinc placement. This was extremely helpful. Good to know how others deal with these issues.
I am not sure whether the leakage I qas observing at the stuffing box currently will warrant an immediate repacking - Minx is out of the water now but when she was in , the leak rate was about a drop every few seconds at rest and then a steady drip underway. We tightened up the gland nut ( I think) and it reduced the rate to about a drip every 4-8 seconds at rest and then a drip every other second underway. I have read that it should be done every few years or so, but I've only owned this boat for a year now and I am pretty sure it hasn't been done in a while. Is it a case of " if it ain't broke, don't fix it" ?
Meanwhile I 'll talk to my mechanical guru about what he thinks --he's game to try the repacking--but we'll definitely find your comments and Don's pdf invaluable.
Also many thanks for the advice on the zinc placement which we'll do also.
Re our location: we are up on the Mighty Delaware River at Riverside NJ.
Where are you other B-27 s? Also, Harley $ Michelle , you mentioned a yahoo Bristol owners list and I wonder if you could share the URL. That would be great.
Thanks,

Dot.
Minx27

[Jim Booth]

Repacking isn't hard. Probably the worst part is getting to it. Sounds like your drip rate is somewhat high. I used the Gore GFO material and it worked very nicely. It's very slippery and didn't need much tightening to stop the drips even though my old flax one had been tightened too tight and the shaft was worn. I didn't do anything to the shaft as it was highly polished by the stuffing. I let it drip a couple to few drips per minute while running but it doesn't drip at all when stopped. It also runs very cool.

Jim

http://www.emarineinc.com/products/gfopacking/packing.html

[minx27]

Dear Don, Harley & Michelle, Jonathan & Co:
Thank you for your responses to my questions about the stuffing box and the zinc placement. This was extremely helpful. Good to know how others deal with these issues.
I am not sure whether the leakage I qas observing at the stuffing box currently will warrant an immediate repacking - Minx is out of the water now but when she was in , the leak rate was about a drop every few seconds at rest and then a steady drip underway. We tightened up the gland nut ( I think) and it reduced the rate to about a drip every 4-8 seconds at rest and then a drip every other second underway. I have read that it should be done every few years or so, but I've only owned this boat for a year now and I am pretty sure it hasn't been done in a while. Is it a case of " if it ain't broke, don't fix it" ?
Meanwhile I 'll talk to my mechanical guru about what he thinks --he's game to try the repacking--but we'll definitely find your comments and Don's pdf invaluable.
Also many thanks for the advice on the zinc placement which we'll do also.
Re our location: we are up on the Mighty Delaware River at Riverside NJ.
Where are you other B-27 s? Also, Harley $ Michelle , you mentioned a yahoo Bristol owners list and I wonder if you could share the URL. That would be great.
Thanks,

Dot.
Minx27

[dinkum1]

Engine/Drive Train Noise

Dear Dot:

We are in Jacksonville, Florida. The Yahoo group is called BristolYachts and is extremely active.

http://groups.yahoo.com/

There is also a Bristol group at Sailnet. Although Sailnet is quit active, it's my impression that it isn't quite as active as the Yahoo group. Here is the Sailnet link.

http://www.sailnet.com/forums/cmps_index.php

Good luck

Harley and Michelle

[keithems]

Don--

Your tech note on repacking the stuffing box mentions replacing the rubber hose just aft of it. I suspect I will have to do that this fall. Can you tell me if that can be done without removing the prop and shaft? If so, how do i get the new hose on? Thanks in advance...