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impeller clearences????

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navyman_98_99

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« on: July 12, 2008, 06:35:25 PM »
What are the clearences for the impeller and how do I go about measuring it? Its a berkeley je pump. Someone told me to measure it through the cleanout hole, but I forgot where to measure and the clearence. My boat since I put a new top loader grate feels like its slipping when romping on it, but then catches and goes! if I remember right, the person I talked to said I may need to shim the impeller, if thats the case where and how do I go about doing that? Thanks for any info



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« Reply #1 on: July 12, 2008, 11:31:00 PM »
If the pump wasn't slipping before u put the loader in then I'd say the loader is whats causing it. Does the loader have a blocker on it? A blocker will block water from reaching the impeller eye, causing it to cavitate on the holeshot.

But to answer your question, you check the thrust (axial) clearance between the thrust face of the impeller and the thrust lip in the housing on a non-shouldered wear ring, and between the shoulder and the impeller thrust face on a shouldered wear ring. For side (radial) clearance you would check with the impeller out of the pump and measure the wear ring with an I.D. micrometer and the impeller wear ring surface area with an O.D. micrometer.
« Last Edit: July 12, 2008, 11:35:46 PM by Jetaholic »
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« Reply #2 on: July 13, 2008, 12:47:41 AM »
thank you for the info, but what is the clearence like thirty thousands or ten thousands. I cant remember the exact clearence to be safe or not safe and have to shim. Thanks again
ohhh here is the loader scoop from cp performance, im not sure if it has a block on it or not???www.cpperformance.com/detail.aspx?ID=3283
« Last Edit: July 13, 2008, 12:56:27 AM by navyman_98_99 »

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« Reply #3 on: July 13, 2008, 02:11:47 AM »
.
1979 Sanger Superjet
BBC, 12JG

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« Reply #4 on: July 13, 2008, 01:28:20 PM »
thank you for the info, but what is the clearence like thirty thousands or ten thousands. I cant remember the exact clearence to be safe or not safe and have to shim. Thanks again
ohhh here is the loader scoop from cp performance, im not sure if it has a block on it or not???www.cpperformance.com/detail.aspx?ID=3283

Usually between .025" and .035". However, if your clearances are the cause of your pump slipping, that would mean you have too much front clearance, allowing the water to bypass the impeller. The recommended way to tighten up the front clearance if needed is to use a shouldered wear ring, then shim the impeller back to obtain a clearance of .025" - .035". Dont do what some do and move the impeller forward by machining the shaft or the impeller nose cone. This method tightens up the front, but loosens up the impeller to bowl distance, allowing a bigger space for water to cause turbulence behind the impeller. Using a shouldered wear ring usually requires the impeller to be shimmed, which tightens up the clearance around both the front and rear of the impeller because it moves the impeller back closer to the bowl, reducing the amount of water that can get back there and cause turbulence,all the while making for a tighter pump all the way around.

It doesn't look like that loader has a blocker in it from what I can see. Try putting the stock rock grate back in and see if your holeshot improves. If it does, try a different loader...it may be either your boat doesn't like that particular loader or your boat may not like a loader at all.

Hope this helps.
« Last Edit: July 13, 2008, 01:30:27 PM by Jetaholic »
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« Reply #5 on: July 13, 2008, 06:41:37 PM »
.025"-.035" is what i was looking for. my boat is a pretty big boat for a jet its a 23.5' glastron cv23 but has a real nice engine I just had built. is it possible to over power a jet? Here is a video of my boat....
[yt=425,350][/yt]http://www.youtube.com/my_videos_edit2?ns=1&video_id=Bbgv1CBOBvk&next=%2Fmy_videos2%3Fpi%3D0%26ps%3D20%26sf%3Dadded%26sa%3D0%26sq%3D%26dm%3D1
« Last Edit: July 13, 2008, 06:44:42 PM by navyman_98_99 »

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« Reply #6 on: July 13, 2008, 07:12:07 PM »
Never had much success using a loader in a larger boat, the only one that really seemed to make an improvement was a 10 to 2 o'clock (most simple of the loaders) which only loads the upper half of the impeller. The real exotic ramp loaders tend to blow out really easily. IMO.
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« Reply #7 on: July 13, 2008, 07:16:47 PM »
Would the wrong (too much) loader hurt your performance? I have no idea what loader is in my boat, but I do know that the last engine it had in it was roughly 2X the HP I am running.
"Don't you realize that there are already enough people in the world to hate without you putting so much effort into giving me another?"

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« Reply #8 on: July 13, 2008, 07:31:59 PM »
This is the only way I know how to explain it but...

Yes it is possible to overpower the pump out of the hole. This is why a lot of people with small impeller cuts run inducers...to keep from blowin' the pump dry out of the hole. On the hole shot the pump has no dynamic pressure in the intake (i.e. pressure obtained by forward movement of the boat and changes with the boats forward speed) to help load the impeller and the engine. A smaller impeller cut won't bite as hard on the hole shot as a larger one will. Because of these factors, a smaller impeller cut can't load as hard as a larger cut impeller out of the hole. Too small of a cut won't be able to provide a sufficient enough load on the engine out of the hole, which allows the engine to spin up too quickly, which blows the eye of the impeller dry, causing the pump to slip out of the hole. Some even run a launch controller on the holeshot to give the pump a chance to hook up without overpowering it.

The whole purpose of a loader is to keep the top of the impeller loaded at speed and help to increase dynamic pressure at the intake. Because of this a loader will increase midrange pull bigtime...but if the loader blocks the intake too much you will sacrifice some holeshot. The main thing is if the eye of the impeller cavitates, you will lose holeshot bigtime.

Here's a great article I found...was written by bp on Hot Boat...explaining what exactly goes on in a pump on the holeshot.

"when an engine is flatfooted off idle, from a dead stop, a significant amount of flow through the pump begins. without the boat being up to speed, restoration of the water to the suction piece is solely based on atmospheric pressure. during those first 2-3 seconds, suction pressure at eye of the vanes on the suction side of the impeller becomes very low, to some negative pressure value (how low the pressure goes is affected by a couple of variables - how much hp is being applied? what is the condition of the pump? what nozzle insert is installed? how heavy is the boat weight/drag effect on acceleration - a heavier boat won't achieve the same speed as a lighter boat; speed increases intake loading velocity, counteracting the low pressure).
pressure at the eye of the impeller can become so low that liquid changes to vapor, causing some degree of cavitation, which negatively affects thrust.
a "cavitation reducer" is a small, mini impeller that is mounted on the shaft, on the suction side of the impeller. the purpose is to increase pressure at the eye of the impeller, to prevent pressure from dropping so low that a change in phase can occur, thus preventing cavitation - consequently it's named cavitation reducer.

a cavitation reducer -might- help you, but then again it might not add what you could be looking for. mine was installed when i had a little over 400hp, and i could tell the difference in acceleration right away. in a heavier layup, with a good tight pump, it can be very helpful in preventing cavitation at the hit. but it's not a cure-all, and needs to be evaluated thoroughly with the rest of the hardware. i've seen guys change impellers, make 1 or 2 laps at the most, jerk it out saying they didn't gain anything. i've seen guys do the same thing with a cavitation reducer. 1 or 2 laps is not sufficient time to gather enough data to make an informed decision, one way or the other. i've seen enough to know they do what they're intended to do, and recently we installed one in my 23' hallett jet along with some other things.."
« Last Edit: July 13, 2008, 07:43:11 PM by Jetaholic »
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« Reply #9 on: July 13, 2008, 07:39:16 PM »
From everything I have learned about loaders, I can say they really are not simple to figure out.

If a pump gets overloaded it really does not change the performance of the jet drive, but it takes driveability away in one place or another, for example; you could have a loader that gets killer top end and keeps the pump loaded while turning but comes out of the hole like a turd (cavitation, blowout etc.) Possibly an inducer would be the answer.

Then again another one comes out of the hole like a rabbit, but blows out while turning or in a rough chop, so the right loader might not be obvious at first.

I think I posted it here before, I said that loaders are like hydroplane props, one boat, one prop. tons of trial and error. Performance parts are never guaranteed to do anything, its what you find that works.

We had an aluminum race boat that had a 10 to 2 loader on it and it worked pretty well, good holeshot and stayed loaded ok too, changed as an experiment to a plate type 12/10/2/6 type really exotic piece and the hull would not even plane, put the same loader on a freinds tunnel hull (also aluminum) and it made a different boat out of it, in fact he picked up almost 5 mph and dropped 100 RPM, wierd :screwy:

Anyway to answer your question, "maybe".
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

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« Reply #10 on: July 13, 2008, 07:41:07 PM »
Also too a loader typically does not do anything positive until around 40mph, so I've been told...
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

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« Reply #11 on: July 13, 2008, 07:46:25 PM »
From everything I have learned about loaders, I can say they really are not simple to figure out.

If a pump gets overloaded it really does not change the performance of the jet drive, but it takes driveability away in one place or another, for example; you could have a loader that gets killer top end and keeps the pump loaded while turning but comes out of the hole like a turd (cavitation, blowout etc.) Possibly an inducer would be the answer.

Then again another one comes out of the hole like a rabbit, but blows out while turning or in a rough chop, so the right loader might not be obvious at first.

I think I posted it here before, I said that loaders are like hydroplane props, one boat, one prop. tons of trial and error. Performance parts are never guaranteed to do anything, its what you find that works.

We had an aluminum race boat that had a 10 to 2 loader on it and it worked pretty well, good holeshot and stayed loaded ok too, changed as an experiment to a plate type 12/10/2/6 type really exotic piece and the hull would not even plane, put the same loader on a freinds tunnel hull (also aluminum) and it made a different boat out of it, in fact he picked up almost 5 mph and dropped 100 RPM, wierd :screwy:

Anyway to answer your question, "maybe".

Very well put. Every boat is different and every boat will respond differently to different parts. Parts that don't work on one boat may work wonders on another boat. One boat's junk is another boat's treasure.
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« Reply #12 on: July 13, 2008, 08:55:28 PM »
wow lots of info to intake!! thanks everyone!! i'll try to get it figured out. maybe a whole new pump, the je pumps intake looks crappy compared to the other pumps. but heare s a bit of info just incase I am running a ford, yea I know ford, but thats what it came with. but its a pretty nice ford, its bored and stroked to a 557 it will run 6500 rpm all day on the dyno but in the boat it runs 5800 rpms with like I said the je pump and an "A" cut impeller top speed is 66 mph gps with the lake flat. but like i said the hole shot is crappy until it catches then its like a rocket! not bad for a 78 glastron that i bought for $1000 and completly redone in a year including engine, paint, all wood, stringers and interior, everythings new! its nice family boat that hauls!! next project is going to be a cole tc2 vdrive strap in and hold on!! Thanks again!!

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« Reply #13 on: July 15, 2008, 09:40:53 AM »
wow lots of info to intake!! thanks everyone!! i'll try to get it figured out. maybe a whole new pump, the je pumps intake looks crappy compared to the other pumps. but heare s a bit of info just incase I am running a ford, yea I know ford, but thats what it came with. but its a pretty nice ford, its bored and stroked to a 557 it will run 6500 rpm all day on the dyno but in the boat it runs 5800 rpms with like I said the je pump and an "A" cut impeller top speed is 66 mph gps with the lake flat. but like i said the hole shot is crappy until it catches then its like a rocket! not bad for a 78 glastron that i bought for $1000 and completly redone in a year including engine, paint, all wood, stringers and interior, everythings new! its nice family boat that hauls!! next project is going to be a cole tc2 vdrive strap in and hold on!! Thanks again!!

Navey I will admit I didn't read this entire thread so I may have missed some things  but I have some questions right off with RPM vs Speed vs HP ,what do you estimate your HP to be at what RPM ,are you confident your tach is correct . I belive your hole shot can be improved but more info and "numbers" will help the diagnosis, re the loader have you checked the horizontal loader bladedepth vs the keel , do you have a pic of the installed loader maybe and also possibly your ride plate adjustment lastly where does this motor "make its power" (power band) according to the Dyno and what cam . Thanks Tom

BTW IMO its unlikley that specific loader really shouldn't hurt your performance  if trimmed and installed correctly, whether its really neccesary in a big boat like that is debatable

 


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