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zetalampi999
04-04-2007, 08:18 PM
I am new to this site and glad I found it. I bought my first Mastercraft last year 1981 Stars and Stripes 351 Ford PCM, I live on a lake in Missouri and go skiing most every morning with neighbors.
I have noticed the engine makes a single loud knock sound...like someone hit it with a hammer only occasionally when running above 3500 RPM the boat seems to hesitate slightly when this happens. I have been using 87 octane and have now switched to 89 octane with plans to switch to 91, hoping this may be the cause. I am also planning on putting new spark plugs in thinking that it will help also. Just curious if it sounds like I am on the right track or way off here.

Willski
04-04-2007, 08:25 PM
Hmmmm. Does it sound like a backfire? I'm sure you'll get a lot of good advice on this issue, but I'm kind of puzzled.

Laurel_Lake_Skier
04-04-2007, 08:28 PM
I don't think the octane or spark plugs would be the cause of that sort of loud knock. It could be the start of a fairly serious problem and has a potential to get much worse. I would start by draining and checking your oil to see if there are metal particles in it.....that would indicate wear on internal parts. It could also be something transmission related. How often does the noise occur? Are you sure the sound is comming from the engine....maybe something is rolling around in the bilge (I'd hope for that)

Slinkyredfoot
04-04-2007, 08:31 PM
Welcome Newbie you first post...Oh do I remember mine...

So the sound you are refering to is like a hammer hitting your block or a knock from like premature fuel detonation??? :D
There is a big diff here...

Willski
04-04-2007, 08:34 PM
Just thought of something else. Sometimes the tranny can make a noise like that if there isn't enough oil. I experienced this. It almost feels like the prop is cavitating, the boat can hesitate, then it catches and makes a kind of loud noise. Check your fluid level.

zetalampi999
04-04-2007, 08:44 PM
Not sure how to tell the Difference between the two sounds Slinky, nothing rolling in bilge area Laurel Lake Skier. The sound is a single knock very easy to hear not a metallic ching but a dull knock I feel a very slight hesitation and it only happens when RPMs are up.

zetalampi999
04-04-2007, 08:48 PM
I will check my transmission fluid Willski I did look at it a while ago and did not notice any low levels I think.

nuckinfutz
04-04-2007, 08:52 PM
1) Has the sound gone away since changing to 91? If it has, thats knocking. Knocking is when fuel pre-maturly ignites in the combustion chamber. This will happen on heavy loads.

2) Does the sound happen under little or no load (not idle and not under load, but in between). If so, usually means a spent main bearing. A spun (AKA "spent") bearing means the rod has play on the crankshaft. The knocking sound (actually like small hammer hitting engine or ticking sound).

Sounds like the first of the 2. You can remedy or diagnose this relatively easy. Add a fuel with high octane (higher the better) see if the sound is less noticable. If it is, you can change the timing to accomadate your fuel needs. Keep in mind, the more you advance the timing, the less power you get. Im assuming your 81 351 is not Fuel injected (guys correct me if Im wrong). Also, tune up can help as well. Plugs, Plug wires, cap, and rotor would't hurt either if they havent been done in awhile. Ive actually seen rust under the cap on a 2 year old distributor in a boat before. We are dealing with water, so believe it can happen. Rust (thats conductive) can and will advance timing once a trail has started in the cap.


Jason

Jerseydave
04-04-2007, 08:59 PM
Hard to diagnose without being there. Start with checking all motor mounts to make sure they're tight. Then check flange bolts at the back of trans. driveshaft. (Neither of these would make the engine hesitate however)

How many hours on the engine? Could be a badly worn timing chain set. Will the engine make that noise if you rev it in neutral? (Don't over-rev it, she's got some age on her!) Could also be carbon buildup in the cylinders. Can be fixed sometimes by pouring water slowly down the carb throat while engine is running. Let someone do this that has done it before!

I would take a good Ford mechanic with you for a ride and try to duplicate the problem. Take the engine box off first.

Good luck!

Willski
04-04-2007, 09:06 PM
Fuel knock usually doesn't present itself as one single loud event. And I also think you would hear it under load at lower RPM. You said you only hear a noise once when you are at high RPM right? Believe me, I'm no mechanic but I am just throwing out ideas. I do have an '84 with a 351 with 1500 hours on it so I've spent little time with the engine!

Slinkyredfoot
04-04-2007, 09:07 PM
Based on what you have said, "knock" and "hesitation" above 3500rpm,peridiocally, I'm thinking it could be just a minor timing problem. I assume you have a 351PCM, Holly 4B carb with points, or have you upgraded you ignition system? Do you have farily new plug wires too???

I had my 79 351 with 900 hrs gone thorough this winter by a very good engine guy, the only thing he saw worn and replaced was my timing chain. At the end of last summer, my boat would "knock" not "hammer" at higher rpms and this probably was my problem...Just a suggestion

zetalampi999
04-04-2007, 09:09 PM
I have only this past fillup used 89 octane I will try the highest octane I can find next and see if it helps. Would the spun bearing be an occasional single knock or more of a repeated Knocks in a row?

Willski
04-04-2007, 09:16 PM
I only use 91 octane in my 84, mainly because the previous owner told me that with 89 octane he did get some knock. Also since you have a purely mechanical distributer with spring advance the engine cannot "sense" knock like newer vehicles and automatically adjust timing for different octanes. Hopefully it is just a knock issue! Much less expensive than the alternatives.

nuckinfutz
04-04-2007, 09:20 PM
yes, I cant express how bad Knock can be over time. A little here and there not so bad. But putting alot of stress on rods, and mains.

Willski
04-04-2007, 09:29 PM
I'm just waiting for something major to happen to my engine! I have owned the boat for 10 years now, and have actually skied behind it since 1988! It has been very well maintained. The most serious engine fix has been new exhaust manifolds last year. I've been lucky.

zetalampi999
04-04-2007, 09:45 PM
Based on what you have said, "knock" and "hesitation" above 3500rpm,peridiocally, I'm thinking it could be just a minor timing problem. I assume you have a 351PCM, Holly 4B carb with points, or have you upgraded you ignition system? Do you have farily new plug wires too???

I had my 79 351 with 900 hrs gone thorough this winter by a very good engine guy, the only thing he saw worn and replaced was my timing chain. At the end of last summer, my boat would "knock" not "hammer" at higher rpms and this probably was my problem...Just a suggestion

Yes a 351PCM, Holly 4B carb no points though...previous owner upgraded the ignition system. My neighbor told me it looked like I was due for new plug wires. I am curious what new plugs and wires along with a timing chain would set me back and can a car mechanic do this type of work?

Slinkyredfoot
04-04-2007, 09:45 PM
I'm just waiting for something major to happen to my engine! I have owned the boat for 10 years now, and have actually skied behind it since 1988! It has been very well maintained. The most serious engine fix has been new exhaust manifolds last year. I've been lucky.

Willski, don't wish something to happen or it might. These older 351 are bullet proof, exhaust headers, hoses, and wear and tear items go bad after a while, enjoy your boat and don't think bad Karma. Take care of your boat as you obviously do and enjoy it......:D

Slinkyredfoot
04-04-2007, 09:49 PM
Yes a 351PCM, Holly 4B carb no points though...previous owner upgraded the ignition system. My neighbor told me it looked like I was due for new plug wires. I am curious what new plugs and wires along with a timing chain would set me back and can a car mechanic do this type of work?

Plug wires 20 bucks, timing chain 15 bucks plus labor, unless you do it by yourself.......Carefree enjoyment....Priceless:....love:

east tx skier
04-04-2007, 10:25 PM
I had my boat do something very similar on my first outing this past weekend. Check your spark plug wires to see if one of them has wiggled loose. I got a very disconcerting pop when I'd get into the middle rpm range. Found the culprit and reattached and problem solved. Changed the spark plug when I got home. Worth a look.

88 PS190
04-05-2007, 01:37 AM
just a question, does your oil look milky at all?

zetalampi999
04-05-2007, 11:56 AM
I checked a few things this morning...the spark plug wires definitely need replaced one even has electrical tape around it where it attaches to the plug. I also checked the tranny fluid it was just barely at the lower of the two lines on stick. Engine oil looks clear amber color no milky look at all I suppose it may only look milky if water were in it and after running engine though.

sbuell
04-05-2007, 02:13 PM
Where are you at in Missouri. Love to see people with the older Stars and Stripes.

zetalampi999
04-05-2007, 04:38 PM
Live year round on Lake Lotawana, been here for 1 year

Slinkyredfoot
04-05-2007, 08:42 PM
Where are you at in Missouri. Love to see people with the older Stars and Stripes.

Hey Zeta, what is your real name??? Post some pics of this boat that is knocking at 3500rpm, we will get it ironed out.....:D

zetalampi999
04-06-2007, 10:29 AM
20565

20566

20567

20568

Here are some pics I have of the boat. The previous owner repainted over the stars and stripes with a black with metallic red flakes.

zetalampi999
04-06-2007, 10:38 AM
Nothing like having a 700 acre private lake in your backyard. Too bad it is 28 degrees right now!
20569

zetalampi999
04-06-2007, 10:39 AM
My name is Steve

chevy08bud
04-06-2007, 10:50 AM
Zeta, it sounds like your problem is ignition related, and not a catestrophic engine problem. My father in law had this problem a year or two ago and we had a hard time figuring it out. I thought that it sounded like an ignition problem, he thought that it was a lower unit problem (I/O). It turned out that there were slight carbon traces inside the cap and the wires didn't look the best, but unless you looked and listened closely, you couldn't tell they were bad. I could hear one of the wires arching at high RPMs. Really weird sound when it happened, but at least it was an easy and cheap fix. I'd get a cap, rotor, plugs, and wires and just replace all of them. Your problem is either comming from the wire that has the tape on it,(it's arching through the tape or elsewhere), or just overall worn components. All of these parts are just pull and replace parts, but if you do need help on replacing any of these parts, just let us know, or shoot me a PM.

wesgardner
04-06-2007, 11:54 AM
If you're still getting knock, RETARD your timing a bit...at the very least, get a timing light and find out where it's set...

Other ignition problems can be solved by this...

http://www.performancedistributors.com/marinedui.htm

You'll still need to set your timing to get rid of the pinging...

M-Funf
04-11-2007, 04:48 PM
Did you solve the problem, Steve?

nice looking boat by the way...Do you have any other pic's of the back seat? I'd like to add one to my '76 soon and I'm still kicking around some ideas...

zetalampi999
04-11-2007, 06:40 PM
20781Haven't had any time or weather to play with boat for a few weeks now. Here is the only pic I could find that you can see the back seat. Fairly simple construction...two marine plywood planks covered with thick foam and vinyl, one sits on end against the transom, the other flat on floor pushed up against other one forming a rudimentary seat.

74stars
04-11-2007, 06:55 PM
Good to see another local S&S- I live in Olathe. Let us know how it runs after your tune-up- I had a heck of a time two summers ago similar thing- found the float was sticking in the secondary side and under load it would lean out and pop and lose power similar to what you are describing. would run great with light throttle on the primary side.

Hoosier Bob
04-11-2007, 09:43 PM
Nice ride Steve. All good advice here so far. I hate to be the one to tell you we already have too many Steve's! You will now have to go by Todd! We definately need more Todd's!8p

Take care Todd!

Slinkyredfoot
04-11-2007, 09:53 PM
Nice ride Steve. All good advice here so far. I hate to be the one to tell you we already have too many Steve's! You will now have to go by Todd! We definately need more Todd's!8p

Take care Todd!

Great idea HB, does this mean I am able to keep my given name "Steve" or will Leroy have to get out he pictures......:D

Hoosier Bob
04-11-2007, 09:57 PM
You are the final Steve my son! I have 24 Todds and then around 60 Gavins available. Not many Love Boat fans?:o Great idea HB, does this mean I am able to keep my given name "Steve" or will Leroy have to get out he pictures......:D