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Low top end rpms

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River man
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Low top end rpms

Post by River man » Mon Aug 13, 2012 8:05 pm

I own a 1977 Lancer with 350k engine and run a 15 x 16 prop through a 1.5 reduction transmission, all original to original specs. My problem is that I top out at about 3300 rpms and 33 mph. The engine will rev to 4500 in neutral. I have been told that if the prop is off the most I would lose (or gain) would be around 200 to 300 rpms. The transmission lags slightly when shifted into gear and makes a fair amount of gear noise in both forward and reverse at idle speed. With no other alternatives I suspect the transmission. Anyone had similar problems and any solutions. I suspect a rebuild would be costly - what about replacement?

jfrprops
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Post by jfrprops » Mon Aug 13, 2012 10:21 pm

what transmission (acutally a shifting unit with some gear reduction) do you have? Paragon? Velvet Drive by Borg Warner?

Does not sound like that is the problem. Wrong prop or binding in cutlass bearing or stuffing box is a possibility too?????

John in Va.
1980 Fairchild Scout 30
19?? custom Argentine Runabout 16'
1954 Whirlwind deluxe dual ckpt 16'
1921 Old Town Charles River 17' (founding Captain, James River Batteau Festival)

River man
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Post by River man » Tue Aug 14, 2012 6:50 am

It runs through a Paragon drive. With engine off I can turn the shaft fairly easily so ruled out cutlass bearing. Stuffing box is fairly loose with some water dripping so ruled that out as well. Not sure there is anything else but transmission.

jamesm2733
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Post by jamesm2733 » Tue Aug 14, 2012 7:48 am

Before rebuilding or replacing the transmission I would check the health of the engine. Does it have good compression on all cylinders? Is the ignition system in proper working order and timing set properly? Is the fuel system and carb in good condition. Any engine will rev up higher with no load applied. As for the noise coming from the transmission, it could be the drive dampener that connects the engine to the transmission. Worn and loose springs will cause a rattle at idle, especially if the engine doesn't run smooth. Best of luck.

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mfine
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Post by mfine » Tue Aug 14, 2012 7:53 am

Engine problems are far more likely than transmission. Could be stuck weights in the distributor advance mechanism. No spark advance would keep you from getting to high rpm under load. Could also be a number of issues with the carb, probably on the secondary side. You may also not be running on all cylinders or have low compression or... Lots of potential issues.

Are there any other symptoms other than it simply won't go faster?

Also, is there any chance the boat is super heavy, like water logged foam?

Tom Gruenauer
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Post by Tom Gruenauer » Tue Aug 14, 2012 7:55 am

I would take it out with the flame arrester removed. Carefully look down the carb at WOT. I don't think your secondaries are opening.
Just my 2cents
Tom

jfrprops
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Post by jfrprops » Tue Aug 14, 2012 8:57 am

I agree with the three good advice comments above....and especially that the noise could be the damper plate. Forgot that.

John in Va.
1980 Fairchild Scout 30
19?? custom Argentine Runabout 16'
1954 Whirlwind deluxe dual ckpt 16'
1921 Old Town Charles River 17' (founding Captain, James River Batteau Festival)

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Paul P
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Post by Paul P » Tue Aug 14, 2012 11:10 am

The prop size and transmission ratio are the stock specification, as is the motor, and the speed noted is right on the money for this boat, but the rpm does not make sense.

I have been tracking the performance of the 23 inboard pretty closely and we have a friend who has a very healthy Chrysler 360 in his with upgraded ignition and everything in tip top condition, and he is reporting 33 mph at 4300 rpm. The speed you are getting sounds pretty good for the 23 hull, it is not a particularly fast hull due to the large wetted area of the deep-v (24-degree deadrise) and the resulting drag, along with the heft of the boat.

The stock prop I believe was 15c16 cupped. That would not make much difference in what you are reporting. Your rpm sounds low, and your speed sounds high...........

At 3300 rpm with that prop and gear, you should be turning 28 mph with 15% drag/slippage. This is not exact but it is close. That is why I think your reported speed is optimistic.

Assuming you are NOT reaching 33 mph, then it makes more sense and I would go after that distributor advance for sure. A new distributor cap won't fix this, but one day with a hot motor I could not get it to re-start at all. I ended up swapping carbs just to see if it was the carb, motor was still hot after the carb swap......still would not restart. Finally I popped on a new distributor cab and VAAAAAAAROOOooooooMMMMM instantly. Never underestimate the value of good ignition cap, wires, coil, condensor. I think Matt got it though, probably distributor advance.

best,

Paul
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

River man
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Post by River man » Tue Aug 14, 2012 3:17 pm

Thanks to all for advice - it gives me options I didn't consider and will try immediately.

The engine does seem to miss occasionally at certain rpms and idled low (I raised the idle). I will check the secondaries visually - assumed they were opening because of the 4bbl kick-in sound. Also assumed advance/distributor was satisfactory given the revs in neutral so thanks for the tip.

Paul, I believe the top speed is correct however as I am measuring via gps as the boat doesn't have a speedometer. That being said it could have been downwind, downriver and thus registering a bit faster. It is turning the stock prop (15x16 cupped).

Again, thanks all - I'm glad to hear these responses - they're more manageble (except the water logged foam issue, which I'll rule out for the moment).

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Capn Taz
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Post by Capn Taz » Wed Aug 15, 2012 8:01 am

How sure are you that your Tach is correct? Depending on if it is stock or not, some aftermarket tachs have a switch to go from 4, 6 or 8 cylinders.

If it is mechanical, the internals could be gummed up, rusted or worn.

If it is electronic some tachs have a calabration screw that could be off.

That could at least answer the correct speed but incorrect RPM issue.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming 'WOW What a Ride!'"

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River man
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Post by River man » Wed Aug 15, 2012 11:04 am

It's a good point except that when I rev it in neutral I get the proper top end - 4500+ rpms

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Paul P
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Post by Paul P » Fri Aug 17, 2012 11:20 am

I still think the culprit is the distributor advance. It would be worth pulling the plate where the ignition points are located, off to take a look down inside to see what you have down there!

Also, sometimes there are more than one issue working against us. Various ignition items come to mind.

On my Sea Skiff I discovered my throttle cable adaptation to the #1409 Edelbrock cab was not allowing the butterfly to open fully. That would still allow the motor to easily reach max rpm in neutral, but it would never develop the full power,

Be sure and set your timing to the dimple at 500 rpm under load if you can, as recommended by cc.


best,

P
1956 17' CC Sportsman, 300-hp
1957 17' CC Sportsman, 95-hp
1966 20' CC fiberglass Sea Skiff, 210-hp+
1973 23' CC Lancer inboard project, 427/375-hp.
1966 38' CC Commander Express, 427/300-hp(2)

So many boats.........so little time.....but what a way to go!!

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