KAD root charger conundrum

[BruceK]

At the end of last season one roots charger was beginning to leak oil past the bearing. I lost 30ml of the 100 in over the season. Thought I may get another season out of it before replacing. After dropping in on Weds I went for a sea trial. I was horrified to find the other roots charger had seized solid and the leaky one dumped a good portion of its oil into the intake tubing.
So thats two roots needing replacing. With nothing to lose I set about stripping them to see if I could salvage 1 good from the two.

How bizzare. The super charger that had seized I stripped down to see if the back plate holding the bearings could be removed and placed on the one that was leaking through. It was seized solid enough that I could undo the nuts holding the front shafts to the respective bearings. Flipping it over to access the back plate I removed the oil housing cover and started on the two bolts that hold the back plate on its dowels. When I removed the first bolt shown in the pic it hissed, frothed as it was being loosened. Suddenly everything came loose. Now what? Is it safe to use or a time bomb? It was absolutely fine last season and I was at a complete loss as to it seizing up. Is there even anything behind the back plate that can hydraulic lock? Nothing shown in the exploded diagrams.

https://imgur.com/ykjTG6r

 

[kashurst]

The fizzing/frothing could just be trapped oil. re the leaking oil is it possible to replace the oil seals and bearings.
The rotors are a very close running fit so it might not take much to jam one. Corrosion or dirt. If it all runs free now I would take it completely to bits and check it for damage/scoring. If its all OK new bearings and seals should be good to go again. How much shaft end float is there in each charger and is it the same in both chargers?

 

[BruceK]

The fizzing/frothing could just be trapped oil. re the leaking oil is it possible to replace the oil seals and bearings.
The rotors are a very close running fit so it might not take much to jam one. Corrosion or dirt. If it all runs free now I would take it completely to bits and check it for damage/scoring. If its all OK new bearings and seals should be good to go again. How much shaft end float is there in each charger and is it the same in both chargers?

The rear bearings in the oil housing are not changeable. If they are gone the whole unit is FUBAR as they get resined in. Front bearings can be readily replaced. I havent checked end float but the whole ensemble now spins freely twisting the shaft by finger tip with just the expected marginal stiffening on compression.
I didn't have time to pull the second one apart. I'm loosing my marbles. It's oil reservoir was still full when I started to take it apart. (after the above post) I'm struggling to determine where all the oil in the intake tubing came from. Current presumption is last year's oil settled and pooled and when it started up it blew it all out. So, it still needs replacing but I will monitor it for one trip and make a judgement call on whether that replacement is now or for the start of next season given this season is almost over.
It's been one of those weekends and I'm wondering if I'm scared of shadows, have a problem, is it fixed, broken, or time bomb.

I think I'll just go and work on tomorrow's hang over

 

[kashurst]

The oil in the inlet pipes could have found its way in over many years or previous owners spilled some etc etc. I would clean it all up, put it all back together now it's free and see how it goes. Even if the 'charger is loosing a bit of oil over a season into the engine it will just get burnt up.

 

[BruceK]

The seized one is separate to the leaking one. Yeah, both went. Mind you on my boat they have a hard life as they cut in and out with the wave crests at 2600 rpm which just so happens to be the same speed I need to take the local waters when they kick up and still plane.

 

[Portofino]

There was a thread a while back about the SC s with the KAD series.
Think from memory I was swimming against the consensus of owners on here saying they were not designed for constant running .Only meant to be for a minute or so until the turbos took over .
Reason for them is to improve acceleration getting up on the plane .
The range ( Kad 300 + DPH legs ) 1400 to 2600 rpm ......this I interpreted as a no go area for the boat.Which for the boat I had at the time was 8 to 22 knots a real PITA tbh .

Think from memory Bruce posted a vid and all we could here was the whine .Explanation ( obvious on the vid btw ) was the heavy head seas , having the throttle back .
A few exchanges later most on here with them seemed oblivious of the 1 min rule .
Quoting Merc SLK ....a completely different blower to the VP one , and PeteM requesting I show the page in the manual to back up my assertions.Concluding because the manual was silent it was thus ok to run constantly within the SC range of revs .
I read it somewhere on a American sport fisher forum re KAD 300 , for trolling etc they fit a switch off switch to kill the SC so they rev them between 1400 and 2600 without the thing whining away wearing out .Remember theses are pros ramping up 1000, s of hrs fishing with fee payers .
They were destroying SC running them high hrs in the range .

So the bearings blow and oil leaks as they overheat with constant running .
Wether a 30 to 80 hrs recreational boater who’s flips his boats every 3/4 years is bothered ....that’s a different question .

 

[BruceK]

Ogura claim their TX range are designed to run constantly at sub 11k rpm IIRC. I dont know what the pulley reduction is but I'd guess the only time one gets to damage these units would be on prolonged kickdown at engine revs roughly 3k if the turbos are worn and kicking in late. However I am in the camp to avoid prolonged SC running and constant kick in and out from the top range. Snatching at those speeds must create a lot of stress. Its not always avoidable though. Its becomes a choice of that or heavy slamming or falling off the plane and having a nasty wallow.

 

[BruceK]

At the end of the day Porto these SCs are now 28 years old. I think given the background they have delivered an excellent service life. Especially when compared to turbos for example

 

[Portofino]

At the end of the day Porto these SCs are now 28 years old. I think given the background they have delivered an excellent service life. Especially when compared to turbos for example

Agree , nothing mechanical lasts for ever , but i am believer where possible offering some sympathy to machinery especially when it’s aged .
eg I never really see N of 1850 rpm ( WOT specced @2200 ) with my “ aged “ 17 y old lumps .
But a lot do need to go near or above 2000 ....because the book / brochure / mag article when new said so .
With the KADs called it a day @3200/3300 tops , 9 years 850 hrs new oil annually etc .As mentioned stayed out of the SC range .
Interestingly never had a SC clutch replaced in that ownership.......a few belts only .
So with all the threads about SC clutches I wonder if my 1 min max running time rule played a part in my KAD reliability experience? Dunno , will never know as only 1 of 1 anecdotal .

 

[tico]

Bruce... check the big O-ring/seal between the airbox and intake pipe. If youve had the airbox off this seal can drop unseen into the pipe and get sucked into the blower. Results in rubber spread over the lobes causing them to stick - or at least thats what happened with mine. Needed careful cleaning of the lobes with solvent before they would rotate freely.