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Message |
    
David Blakey
New member
Username: catboater
Post Number: 1
Registered: 07-2007
| | Posted on Sunday, March 30, 2008 - 04:10 pm: | 
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When I engage the forward gear, my engine acts like it's under a real strain. I have to rev it to 1800 to 2000 rpm before putting it in gear to keep it from choking down, and I see an rpm drop of nearly 1000 rpm when it's in gear. Doesn't happen going into reverse, just forward. This has been a slowly progressive problem since last fall, but last summer it wasn't doing this. I debarnacled the prop, which helped a little, but not much. The stuffing box drips like it's supposed to so I don't think it's overly tight. An archive search on this site turned up carburetor settings and exhaust blockage as possible culprits, but I've been thinking there's a bind on the prop shaft somewhere. Any suggestions? |
Richard Shapiro
Senior Member
Username: mainesails
Post Number: 51
Registered: 09-2005
| | Posted on Sunday, March 30, 2008 - 05:49 pm: |
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I can’t diagnose your problem, but I do have some thoughts …
Of the things you mention, in my mind the least likely is prop shaft binding.
Here are some other possibilities:
Top of my list would be the carb. The most likely possibility would be a clogged high speed needle. Other possibilities include a loose needle (adjusting itself due to vibration) or a leaking float.
Next on my list would be a bad spark plug or a bad wire. If they’re old, you should replace the lot, along with the points, condenser etc.
After that would be an exhaust blockage, but I’d check the prop shaft first, because it’s easier. As to the exhaust, you’d have to disassemble the system (preferably starting with the connection at the manifold). If it’s been together for a few decades, it would be a bear.
I’d also check the motor mounts to see if the engine has come loose and is badly misaligned with the shaft (rot in the beds is the general culprit here).
Finally, I’d check the prop and shaft. Assuming you don’t have a big hunk of rope on your prop, the only possible bind points are:
1) Cutlass bearing area - grab the prop and shake it from side to side. There should be a little (1/32”) of free play in the cutlass bearing. If there is no play you likely have some kind of obstruction.
2) Stuffing box - I would consider repacking the stuffing box if it hasn’t been repacked in the last couple of years.
3) Engine/Reverse gear:
Put the engine in neutral and turn the prop by hand (in both directions). It should take only a couple of pounds of force to turn it.
You can also turn the output flange by hand. If in doubt, you can unbolt the flange from the reverse gear and try it. With the flange unbolted, I would also turn the motor’s output flange. In neutral, it should turn with little resistance. In gear, you shouldn’t be able to turn it without moving the flywheel.
If none of these things turn up problems, I’d check for binding in the alternator, water pump etc. After that, you get into internal problems.
I hope this helps. |
Richard A. Day Jr.
Senior Member
Username: richardday
Post Number: 575
Registered: 11-2003
| | Posted on Sunday, March 30, 2008 - 08:58 pm: |
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I suggest with the engine off and prop drive coupling bolts removed put the reverse gear in nuetral and rock the flyweel to get a feel for how much torque it takes. You could remove the spark plugs to make it easier if you need to. Put the reverse gear in reverse and rotate the engine counter clockwise just the same as the engine rotates in operation. Feel for any change in the torque required. Put the reverse gear in forward and see if there is a change in the torque required to rotate the engine and reverse gear. I am suggesting you need to separate the problem area. prop shaft stuffing box prop area from internal reverse gear problems. The fact the engine does seem under load going astern suggests to me the prop and shaft, stuffing box etc are not the problem. I suspect the ball bearings in the reverse gear are not the problem. Have you checked the oil level at the aft end of the reverse gear it should be about 1 inch below the shaft. Keep in mind the engine oil and reverse gear oil are not connected in any way. When you go in revese you are grasping the the large drum portion of the reverse gear and it stops rotating. When this happens the sun and planet gears come into play and if the ball bearings were messed up I would expect you to be having trouble with the reverse operation. When you go ahead the drum revolves and the clutch plates are compress and held tightly by the cone snapping forward in turn the fingers keep the clutch plates tight. I am wondering if the drum is being held by the take up nut #330 on the reverse band. In effect you may have the reverse band too tight and when you try to go ahead something is causing the reverse function to fight the forward function. I may be way off base but for what it may be worth. My thoughts!! |
Richard A. Day Jr.
Senior Member
Username: richardday
Post Number: 576
Registered: 11-2003
| | Posted on Sunday, March 30, 2008 - 09:05 pm: |
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The fact the engine does NOT seem under load going astern suggests to me the prop and shaft, stuffing box etc are not the problem.
Sorry for the omission of NOT |
Richard Shapiro
Senior Member
Username: mainesails
Post Number: 52
Registered: 09-2005
| | Posted on Sunday, March 30, 2008 - 10:42 pm: |
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I think Richard has an excellent suggestion re the reverse gear.
If not, I know that there are a lot of possibilities, but I keep coming back to three things.
First, rpm drop in forward only is a classic symptom of a lack of power (due to the reverse only reduction gear - the engine is far less loaded in reverse). This is pretty much what the engine would do if one cylinder was not firing, the carb is clogged etc.
Second, the engine bogs immediately, and not after a few seconds, so I'd not immediately suspect the fuel pump.
Third, the fact that it came on slowly over the fall is another hint. It rules out sudden failure problems. This also suggests a tuning issue
I think it'll be a matter of eliminating one possibility at a time. The only real fly in the ointment is if your exhaust manifold is blocked and rotted away - have it welded - it is irreplaceable. |
Harry Wrede
Visitor
| | Posted on Monday, March 31, 2008 - 10:11 am: |
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Have you checked the distributer centrifical advance? This could also be a problem |
David Blakey
New member
Username: catboater
Post Number: 2
Registered: 07-2007
| | Posted on Monday, March 31, 2008 - 10:42 am: |
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Thanks to all for your suggestions. They help me make a pretty straightforward list of things to check.
The engine was torn down and rebuilt by the previous owner, and has run well since the rebuild; that doesn't guarantee that there are no major internal engine problems, but hopefully makes that an unlikely casue of the problem. Because of a starting problem, I just tuned the engine a month or so ago- new points/plugs and checked the timing. That fixed the starting problem but had no impact on the rpm drop. I've checked the oil level in the transmission and know it's OK.
I'll probably start with the carb, because it's easy, and go from there.
How do you check the function of the centrifugal spark advance? If I'm not mistaken the mechanism for that is under the breaker plate in the distributor, but beyond visual inspection I'm not sure how to check it to make sure it works. |
Harry Wrede
Visitor
| | Posted on Monday, March 31, 2008 - 11:32 am: |
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Remove the breaker plate and make sure the centrifical weights are moving freely and lightly lubricated. Also make sure the springs are not broken. |
Richard Shapiro
Senior Member
Username: mainesails
Post Number: 53
Registered: 09-2005
| | Posted on Monday, March 31, 2008 - 11:49 am: |
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I time my Palmer and check the advance with an auto timing light.
Clamp a wire around the number 1 spark plug wire, put the other lead to a 12 volt source, and run the engine.
Set the timing by unclamping and rotating the distributor. You can see a chisel cut on the flywheel and the engine block. The light should fire a 0 degrees advance at idle. If you advance the throttle, the timing should advance. |
David Blakey
New member
Username: catboater
Post Number: 3
Registered: 07-2007
| | Posted on Monday, March 31, 2008 - 03:15 pm: |
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OK, simple enough. Thanks again. |
Todd Vidgen
Member
Username: todd_vidgen
Post Number: 11
Registered: 03-2008
| | Posted on Tuesday, April 01, 2008 - 04:53 am: |
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I dont know anything about this engine/gear box assembly,but a slow degeneration suggests wear,
If you have not changed anything,ie timing,carby
settings etc(which do not change if you are not
using the machinery).
In some motor assy's I have repaired ,as wear occurs
the gear box "drags" one gear whilst being selected
in the other.
Just a thought .Todd |
ChipG
Visitor
| | Posted on Tuesday, April 01, 2008 - 07:54 pm: |
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Hello David,
I had a similar issue two years ago. In my case, it wound up being a sticking valve on the number four cylinder. Thanks to the trouble shooting help from this group, I wound up simply removing the spark plug and squirting some Marvel Mystery Oil in the area around the valve. I rotated the flywheel by hand and was able to get it to unseat enough to let some oil go inside the hole as well... used a WD40 tube to reach inside... but squirted MMO... not WD40. I let it sit for about 10 minutes or so and then ran the engine for about 20 minutes at various speeds including very high RPM. I have not had any problem since that time. Best wishes David. Love to hear what resolves your issue. |
David Blakey
Member
Username: catboater
Post Number: 4
Registered: 07-2007
| | Posted on Wednesday, April 02, 2008 - 11:08 pm: |
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Chip,
How did you determine that a sticking valve was the problem? Compression check? |
ChipG
Visitor
| | Posted on Friday, April 04, 2008 - 01:41 pm: |
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Yes. Very informal compression check though. I used a rubber glove on my hand... placed my thumb over the spark plug hole and then rotated the fly wheel. When I found the cylinder with the problem, I shined a flash light in through the spark plug hole and watched the valve motion as I rotated the flywheel manually. Best wishes. |
David Blakey
Member
Username: catboater
Post Number: 5
Registered: 07-2007
| | Posted on Sunday, April 20, 2008 - 04:06 pm: |
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Just to close the loop on this thread: When I had a chance to get back to troubleshooting my engine problem, I found stuck valves in TWO cylinders (numbers 3 & 4). After soaking the valve shafts with MMO, waiting, then tapping the valves to break them loose, I got compression back and the engine runs great.
Beyond adding MMO to the fuel (which I had not been doing but will from now on), is there anything to do to prevent the valves from sticking? This engine has no more than 8-10 hours use since it was rebuilt, and it's a bit disconcerting that valves are already sticking. Also, it seems from my experience and other posts I've read that the back cylinders seem to be more prone to sticking. Any particular reason for this?
Thanks again to all who responded. I think I'd have been in a pickle if I'd had to rely on local "professional" help to sort this out. This board is a great resource for those of us who are learning to care for these engines. |
Richard A. Day Jr.
Senior Member
Username: richardday
Post Number: 584
Registered: 11-2003
| | Posted on Sunday, April 20, 2008 - 05:32 pm: |
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I think you may be getting water in the two aft cylinders. Any blockages in the exhaust line or any way when you shut down a vacuum forms in the exhaust line and pulls water back up the exhaust pipe. Some people put a vacuum breaker pet cock in the exhaust line to insure when shutting down there can be no vaccum build up. Others simply put a 1/4" copper line over board from the high point next to the engine. This automactically breaks any vacuum and you can look over the side from time to time to make sure it is spitting cooling water. |
David Blakey
Member
Username: catboater
Post Number: 6
Registered: 07-2007
| | Posted on Monday, April 21, 2008 - 04:43 pm: |
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Richard,
My exhaust system is plumbed with an arch of hose spanning the elbow which is at the lowest point in the system. This hose arches up to a point above the waterline and I suspect was put in to prevent back-siphoning through the transom exhaust outlet. I thought such loops were supposed to be vented but this one isn't- it's just a solid length of hose. If I put a vent fitting at the top of this loop, will it prevent the sort of vacuum you're talking about? That would be an easy fix if it would work.
Also, I recently read in a maintenance article about Atomic Fours a recommendation against extended cranking of an engine that fails to start, the idea being that while cranking, the raw water pump could pump water into the cooling jacket and without any exhaust pressure (since the engine hasn't yet started)this water could get from the water jacket into the cylinders. If that's really possible, I must confess to being guilty of doing that recently; that could be how water got in. |
Richard A. Day Jr.
Senior Member
Username: richardday
Post Number: 586
Registered: 11-2003
| | Posted on Monday, April 21, 2008 - 07:20 pm: |
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I suspect the extended cranking may have allow water to get into the cylinders. |
