SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: dat1dsm on July 31, 2014, 01:34:13 PM
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Well sad news today =( I took my oil pan off and all that good stuff off to replace my rear main seal and my thrust washer/bearing came off. Went to machine shop get new ones and they told me they never in their 40 years seen this. What I thought was just get new one and replace, it's not so simple. I thought the bearings that came off where like that just worn out but when I went to machine shop they told me that my thrust thrust washer wasn't supposed to be like that, it's supposed to be like this. I have the worst luck ever
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Anyone have a good crank? 69-71 BBC 4 bolt main 2 piece rear main
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Anyone have a good crank? 69-71 BBC 4 bolt main 2 piece rear main
I might. I'll check when I get home tonight.
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Thanks
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Bummer, well when you go through your engine and freshin it all up, make sure you check and adjust your crank end play correctly, and find out if your pump or anything else is loading the back of your crank too much, then you will be faced with that same problem again in the near future. I like to set crank end play in a jet boat engine someware between .006-.009.
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You need a minimum of 1/8" clearance between your driveline yoke and the snap ring on the front of pump shaft & thrust bearing.
Try Castillos Crankshaft Specialist14654 1/2 Firestone Blvd, La Mirada, CA 90638, they might be able to repair your crank.
Good luck,
Joe
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Been down this road before. Check out RPM cranks....even though it's Chinese shit, it was the sexiest crank I ever saw...made my scat crank look like scrap. Like has been said, give up some spline engagement for clearance....the boat will flex. Leave 1/8-1/4" slop
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Bummer, well when you go through your engine and freshin it all up, make sure you check and adjust your crank end play correctly, and find out if your pump or anything else is loading the back of your crank too much, then you will be faced with that same problem again in the near future. I like to set crank end play in a jet boat engine someware between .006-.009.
What do you mean as in pump? oil pump?
You need a minimum of 1/8" clearance between your driveline yoke and the snap ring on the front of pump shaft & thrust bearing.
Try Castillos Crankshaft Specialist14654 1/2 Firestone Blvd, La Mirada, CA 90638, they might be able to repair your crank.
Good luck,
Joe
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I think what it was, before I rebuilt my jg jet, reason for being rebuilt, my shaft was worn to shit, the a-pellar was missing half the blades and it had at least half an inch of play. In n out. Hence why I rebuilt the jet. Could that caused the problem to my crank?
Also, the jet was Makin a loud knocking noise before I built it. Crazy thing is , motor ran fine and strong. only reason I found this problem was because I was replacing my leaking rear main seal
Been down this road before. Check out RPM cranks....even though it's Chinese shit, it was the sexiest crank I ever saw...made my scat crank look like scrap. Like has been said, give up some spline engagement for clearance....the boat will flex. Leave 1/8-1/4" slop
How do I go or check about that clearance. Sorry. I'm a newb. My first jet boat. I'm used to my turbo cars and not these big blocks
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Wow, sounds like you have/had a lot going on. If you didn’t replace your jet pump shaft, the splines on the shaft could be twisted. It is also possible that the splines in your driveline yoke could be twisted as well. Both of these conditions will cause your “slip yoke” to lock up on the jet pump shaft and will apply extreme pressure to your crankshaft thrust bearing. The driveline yoke should easily slide all the way back to the snap ring without binding.
Some other concerns, if the jet pump thrust bearing failed or the bearing cap had come loose, either could have let the pump shaft push forward, loading the driveline and therefore loading the crankshaft thrust bearing.
Something to think about, drag boats can have bowl pressures in the neighborhood of 400PSI with spikes to over 450PSI. Pressure generated will affect all surfaces inside the pump including the discharge (bowl) side of the impeller, forcing the impeller forward. This forward force is resisted by the jet pump thrust bearing and the bearing cap. Using the formula, Force = Pressure * Area (F=P*A) for a boat with an A impeller (9”diameter) producing 200PSI bowl pressure, the force on the thrust bearing and cap would be:
A = pi(R)^2 = (4.5)^2 * 3.14 = 63.6 square inches
F = 200 PSI * 63.6 sq/in = 12,723.5 lbs
Even if we just consider the area of the 7.270” diameter hub of the impeller:
A = pi(R)^2 = (3.635)^2 * 3.14 = 41.5 square inches
F = 200 PSI * 41.5 sq/in = 8,302.1 lbs
Let’s compare that to the crankshaft thrust bearing which has an annular area of 3.127 square inches. With an oil pressure of (an exaggerated) 100 PSI, the theoretical thrust forces that would not overcome the oil flowing (at this pressure) between the crankshaft and thrust bearing would be:
F = 100 PSI * 3.127 sq/in = 312.7 lbs
There is not enough oil pressure and surface area to generate a hydrostatic lubrication film and the hydrodynamic lubrication film is quickly dissipated. Flowing oil will take the path of least resistance and with .006-.009 of endplay, that clearance is already greater and will flow more oil than the clearance between the main bearing and crank journal. When the driveline yoke locks up on the jet pump shaft, all of the crankshaft thrust clearance is taken up. All of the oil takes the path of least resistance and escapes out of the front of the thrust bearing. The end result is what you now see.
You can check the yoke clearance in a 4-point mount easier than in a 3-point mount. You can unbolt the driveline from the PTO and slide it back on the pump shaft. This will indicate your end clearance. On a 3-point mount, this will have to be done through the access hole.
Don’t forget to check for binding in the splines and that the bearing cap is tight.
Good luck,
Joe
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Thanks
Sorry late night! I'll check today.
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Wow, sounds like you have/had a lot going on. If you didn’t replace your jet pump shaft, the splines on the shaft could be twisted. It is also possible that the splines in your driveline yoke could be twisted as well. Both of these conditions will cause your “slip yoke” to lock up on the jet pump shaft and will apply extreme pressure to your crankshaft thrust bearing. The driveline yoke should easily slide all the way back to the snap ring without binding.
Some other concerns, if the jet pump thrust bearing failed or the bearing cap had come loose, either could have let the pump shaft push forward, loading the driveline and therefore loading the crankshaft thrust bearing.
Something to think about, drag boats can have bowl pressures in the neighborhood of 400PSI with spikes to over 450PSI. Pressure generated will affect all surfaces inside the pump including the discharge (bowl) side of the impeller, forcing the impeller forward. This forward force is resisted by the jet pump thrust bearing and the bearing cap. Using the formula, Force = Pressure * Area (F=P*A) for a boat with an A impeller (9”diameter) producing 200PSI bowl pressure, the force on the thrust bearing and cap would be:
A = pi(R)^2 = (4.5)^2 * 3.14 = 63.6 square inches
F = 200 PSI * 63.6 sq/in = 12,723.5 lbs
Even if we just consider the area of the 7.270” diameter hub of the impeller:
A = pi(R)^2 = (3.635)^2 * 3.14 = 41.5 square inches
F = 200 PSI * 41.5 sq/in = 8,302.1 lbs
Let’s compare that to the crankshaft thrust bearing which has an annular area of 3.127 square inches. With an oil pressure of (an exaggerated) 100 PSI, the theoretical thrust forces that would not overcome the oil flowing (at this pressure) between the crankshaft and thrust bearing would be:
F = 100 PSI * 3.127 sq/in = 312.7 lbs
There is not enough oil pressure and surface area to generate a hydrostatic lubrication film and the hydrodynamic lubrication film is quickly dissipated. Flowing oil will take the path of least resistance and with .006-.009 of endplay, that clearance is already greater and will flow more oil than the clearance between the main bearing and crank journal. When the driveline yoke locks up on the jet pump shaft, all of the crankshaft thrust clearance is taken up. All of the oil takes the path of least resistance and escapes out of the front of the thrust bearing. The end result is what you now see.
You can check the yoke clearance in a 4-point mount easier than in a 3-point mount. You can unbolt the driveline from the PTO and slide it back on the pump shaft. This will indicate your end clearance. On a 3-point mount, this will have to be done through the access hole.
Don’t forget to check for binding in the splines and that the bearing cap is tight.
Good luck,
Joe
Yeah. I think it was the previous jet that was in the hull when I bought it. The jet ended up being so thrashed it wasn't rebuildable. Has to much thrust play that it kept scraping back and forth till it cracked the jet housing. But now I got a fresh blue printed jg back in there. Like I said, didn't have any symptoms of bearings being out or anything. No knocking or anything like that. Reason I found that bearing like that was because I was replacing rear main seal.
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Any pics of the damaged area on the crank? Unless you can find a scorching deal on a crank, talk to castillos to see if you's is repairable.
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Any pics of the damaged area on the crank? Unless you can find a scorching deal on a crank, talk to castillos to see if you's is repairable.
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No pics. Was little to upset. I just cleaned up and went inside lol. But here's a pic of what is going on. The bearing itself made its on grove and cracked here
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I missed that it was cracked. I'm sorry, I was hoping for the best.
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My crank is from a newer block, 90-91 Mark IV.
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I agree with Flusher, send that pic to Castillo and see what he say's. If he check's it out,can fix it and polish it for you, you'd be ahead of the game.
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Any pics of the damaged area on the crank? Unless you can find a scorching deal on a crank, talk to castillos to see if you's is repairable.
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Once my local machine shops has a crank already cut to " 10 10" $175.. going to take my block to machine shop first to have further inspection and make sure nothing else got ruined. Anything I should tell machine shop to do since their in there already? I might as well get new rings , and bearings all that. Anything in particular I should tell them to do? Not sure on jet boat motors. Don't know too much on specs and clearances and all that. I heard that they take less of compression on rings? Or something like that