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70sprint
Sailor
Canada
16 Posts |
 Posted - 10/30/2009 : 17:32:45
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I'm hoping someone here can help, I've spent the entire summer trying to fix this problem. I have a 1970 26' Pace Sprint open cruiser. I re-powered with a 350 mag MPI merc, since the re-power the boat loses grip at about 2500 rpm. At first this was seen as a transmission problem... however my mechanic insists it is not, he has pulled it apart and put back together, pressure guage indicates no pressure loss during the "slip". New prop purchased and cupped (several props tried) nothing is working to remedy.
Symptoms: engine revs, boat slows at 2500 rpm. It will "catch" and "release" if I stay on the throttle.
Any suggestions welcome.
thanks,
Jeff |
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32pacemaker
Buccaneer
USA
27 Posts |
Posted - 10/30/2009 : 18:51:42
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| do you mean that the prop is cavatating and then biting,or cavatating and then continuse to rev higher while still cavatating. if you have a 1:1 transmission and you hook up a timing light to a spark plug wire put a mark on the prop shaft and point the timing light at it and you can tell if the trans is slipping or the prop is cavatating |
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joebobb
Forum Admin
USA
444 Posts |
Posted - 10/30/2009 : 18:51:42
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Hello Jeff,
What do you mean by "catch and release"? Do you mean that it will alternately load up and accelerate on the one hand, and then rev freely without gaining (or perhaps losing) speed on the other?
Without information that leads me to believe the contrary, I would tend to agree that it's a transmission problem. Unless you've done something to the underside of the hull to change the hydrodynamics, I can't envision why this boat could be somehow cavitating so much as to behave in this fashion. It could be that your mechanic had assembled something incorrectly. If there is a problem with the clutch pack, for instance, then even if the line pressure in the trasmission is within specification, the transmission could still slip. You mention no pressure loss - but is the pressure within specification? A worn front pump might generate a constant pressure, but insufficient to engage the clutch fully.
Kind regards,
JoeBobb |
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joebobb
Forum Admin
USA
444 Posts |
Posted - 10/30/2009 : 18:54:42
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Ha! 32Pacemaker - we replied at the same time! I was writing my reply and I saw yours when I hit the "submit reply" button!
I think your suggestion is really sound. I had never thought of that technique before, but you are right - for a 1:1 transmission, that should reveal slipping pretty quickly...
Kind regards,
JoeBobb |
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Morning Wood
OLD SALT
USA
429 Posts |
Posted - 10/30/2009 : 18:55:25
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What about the key way on the prop? It could be worn and allows the prop to slip when the torque gets higher. Also check the linkage for your clutch. Make sure it is going all the way in gear forward. That too will cause it to slip at higher RPMs.
Good Luck. |
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changeofpace
OLD SALT
340 Posts |
Posted - 10/30/2009 : 20:42:29
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| Or maybe the flange on the shaft that connects to the tranny is slipping |
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32pacemaker
Buccaneer
USA
27 Posts |
Posted - 10/30/2009 : 22:34:47
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| another mark and the timing light,But I dont think it's the prop key the propeller has been changed numerious times |
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desperado2
Buccaneer
USA
36 Posts |
Posted - 10/31/2009 : 00:36:15
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70sprint
We ran a 28 pacemeker with twin CH270 350CI as a towing vessel for 14 years. We had a similar thing happen on one engine. When you brought the vessel up on plane the engine would surge in and out of gear (slipping) Once the vessel was up on plane the problem corrected itself. This was 72c B&W 1:1 trans. The soliution was simple after many hours of problem searching. The high angle the vessel prior to getting on plane was causing the Trans to starve for oil, we slightly over filled the trans and our problem was solved. Hope you solution maybe as easy. |
Capt Dennis C. Warwick
Desperado II 73' MY 40
Seneca Creek, Maryland |
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70sprint
Sailor
Canada
16 Posts |
Posted - 11/06/2009 : 14:58:44
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Hi all,
Thanks for your input. To answer a few questions. The shaft flange has been replaced, 3 different propellers have been tried. trans oil pressure within limits. Another 1:1 was tried in the boat with same result.
The slip occurs at about 2500 rpm, where the engine revs up.. but not as much as i have experienced with cavitation in the past. the boat with "grab" again with reduced throttle or an increase in throttle. more throttle = more slipping and catching.
The transmission is the original from 1970, and has been reworked many times i'm sure. I had the clutch packs recently replaced and the whole transmission was overhauled.
The hull has also been painted and painted over, would this uneven surface be enough to generate air pockets in the prop? should I bother with the old trans? or just grab a new 1:1? I'm already into the cost of a new one in repairs from this problem.
thanks,
Jeff |
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joebobb
Forum Admin
USA
444 Posts |
Posted - 11/06/2009 : 18:32:13
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Hmmm - so you've tried more than one transmission? Well, that would tend to eliminate the transmission as a problem. I thought for a moment that there could be another, transmission-related issue, such as a blockage in a cooler line or a blockage in the cooler itself, but you mentioned that the pressure is within acceptable limits. Could it be stumbling/missing of the engine itself? You do mention "more throttle = more slipping and catching". If the engine itself is stumbling or missing as the rpms increase, there could be a large number of potential causes: fuel-starvation due to clogged filters/jets, ignition problems due to maladjusted points, worn distributor shaft, etc. From your laundry list of changes - everything from the prop to the transmission - the only part of the driveline that has not been discussed has been the engine itself.
Kind regards,
JoeBobb |
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70sprint
Sailor
Canada
16 Posts |
Posted - 11/09/2009 : 11:34:44
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Hi Joebobb,
when the boat slips, the engine revs out (boat slows); but will catch again and more RPM can be applied until the next slip... if I pull off the throttle the boat will catch very quickly. The boat seems to be pretty reliable around 19mph. I don't know how fast these hulls are designed to go, my gut tells me a sand/repainted hull will lessen the chance of air getting into the prop. (if it's the prop).
Very Frustrating.
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70sprint
Sailor
Canada
16 Posts |
Posted - 11/09/2009 : 16:22:15
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Hi All,
I just spoke with my mechanic (not the one that re-manned the trans). He thinks the transmission has been put back together improperly and fwd is actually reverse??? this is why it is slipping with throttle. Can anyone verify this could be the case???
thanks,
Jeff |
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32pacemaker
Buccaneer
USA
27 Posts |
Posted - 11/09/2009 : 17:40:51
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| yes the trans shift lever will be in reverse at the transmission, again use your timing light and see if you really have slipping |
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joebobb
Forum Admin
USA
444 Posts |
Posted - 11/09/2009 : 19:35:17
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Jeff, I just sent you a Borg Warner Manual for these Velvet-Drive transmissions. It should help you do a little troubleshooting. I don't understand what the term "engine revs out" means. Do you mean that the engine rpms suddenly spike upwards? I don't think air getting to the prop has anything to do with this issue. If the transmission is somehow running in reverse during forward motion, you should be able to tell easily...the transmission output shaft will be turning the opposite direction as the engine. I would be pretty amazed if this is the case - mainly because the selector lever (thus the lever at the bridge too) will be in "reverse" - which should be pretty obvious. And then, of course, the propeller rotation would have to be the opposite as well...
Kind regards,
JoeBobb |
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70sprint
Sailor
Canada
16 Posts |
Posted - 11/27/2009 : 13:20:10
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Hi JoeBobb,
By revs out, I mean the RPM increases slightly until the "catch" when RPM decreases to the normal level for that boat speed. so not a complete blow out, like cavitation usually is.. more of a clutch slip and re-engagement kind of feel.
I'm having the trans pulled, checked for correct pump rotation and clutch pack and basket checked. Thanks to everyone for your input, I'm hoping to post a resolution soon.
thanks,
Jeff |
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jackel
First Mate
55 Posts |
Posted - 03/08/2010 : 17:22:45
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hi spirit70,
just so you know,
my 72 32' pacemaker w/ 350 crusaders, and velvet drives operate opposite to each others respected rotations.the velvet drives I have are 91:1 and if one engine is rotating (counter clock-wise), the output at the rear of the trans. is (clock-wise). therefore, the port engine turns clock-wise, and starboard turns count-clock-wise.
regards, Jackel |
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Topic |
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HELP! 2500 RPM blow out
