Rebuilding Power Head

[funpilot]

Re: Rebuilding Power Head

Brian, I used just a Clymer when I rebuilt my 90 in May. Some of the 'Use a Factory Manual' crowd can be pretty vocal, I always wonder if that's the case do they use just the manual or do they rely on Experience, Technical School Background, or other knowledge? I've seen and written both good and bad manuals in my day, and I certainly don't approach a project with just an empty head. If I don't think the manual is good, I'll improvise. Don't worry about the dental pick, your finger nail will tell you a lot, and the final test is how smoothly the crank and pistons rotated before assembling the crankcase halves.

By the way, were you surprised that I was correct? LOL!

With regard to your linkage, they won't really tell you how to adjust the shifting mechanism, but you do have to assure that your cable housing relative to the cable is the correct length, it should be adjustable, and often needs to be lengthened to make up for cable stretch. Just a thought regarding your shifting difficulty. The throttle linkage has 'looseness' built into it, and my approach was to remove as much of that looseness as possible by renewing the nylon bushings and the cam to cam follower bushing. Cheap insurance to start the link and synch with.

fp

 

[MASTER Brian]

Re: Rebuilding Power Head

No, I wasn't suprised you were right, I was just suprised to see it in the Clymer, when the OMC manual was so strict about that tool.

Everything should be the correct length, unless something shrunk or stretched out in the month or more it's been apart. Not being sarcastic, I'm really beginning to wonder.:^

Probably not a bad idea to replace those things. If things don't look up soon, I might do that.

 

[funpilot]

Re: Rebuilding Power Head

Brian, I didn't think you were being sarcastic and I admire your perseverence. I did adjust my cable housings slightly when I rebuilt my powerhead because they didn't seem to be located in neutral quite correctly. Adjusting them solved that problem.

Keep working... you'll get there.

fp

 

[MASTER Brian]

Re: Rebuilding Power Head

Well, I've torn into the carbs, not so bad, once you figure out what they want removed. Hopefully they go together smoothly.

One thing I did notice is in the kit, it includes a new valve seat, which is the large "plug" right under the float, that takes a large flat head screwdriver to remove. Anyway, the new one has a different size opening than the one that was on the carb. The manual says to replace the gasket, but not the seat. Since the new one is a different size, I'm assuming I shouldn't replace it, just the gasket. Am I correct?

There sure seems to be a lot of left-over parts in the kit, I hope this is normal. I'm sure it has to do with the fact the kit is for a V4 or a V6.

 

[MASTER Brian]

Re: Rebuilding Power Head

SHE LIVES!!!8)

I still think there may be some small kinks to work out, but all in all, she seems to run very well.

Shifting may need some tweaking, but there isn't any grinding and it goes foward, reverse and neutral. It just feels a tad off. Maybe it's just different??

I also want to run through the timing and idle once more to double check it all. It seems like it may be a little rough on idle, but the tach says right around 600-700. I believe the manual calls for 650.

We set the timing at 25 BTDC. The manual calls for 30, but the cover on the carbs says 28, so we split that and then took 4 off for Joe Reeves method.

I've gotten through the 2nd hour (per the manual) and am just about out of pre-mix fuel (12 gallons mixed at 50:1 in addition to the VRO). The VRO is working fine, do I need to pre-mix in the tank for the next 8 hours or not?

The boat seems a bit sluggish on take off, but after plain, it does great and has great acceleration. Not sure if this is the 3 blade prop, it seemed a bit better before. I'm guessing most of the things I noticed are due to double oil and the fact I'm sure I'm aware of every little thing now.

One more thing, worth noting, I did replace a few magnets and I saw something recently saying that if magnets are replaced the flywheel should be rebalanced. So I think I'll pull it and have it checked.

Thanks again for all the help, especially FP and KY, you guys are great!

 

[funpilot]

Re: Rebuilding Power Head

Brian, you're welcome. Sounds like things are looking up.

I go with 12-15 gallons of premix, and then I figure I'm good.

The change to straight fuel and the VRO will not make as great a difference as you are expecting. Cooler weather and denser air will make a difference.

One thing you should do is re-torque the heads (you should be able to just snug them down, you don't need to go through the entire proceedure) and retorque the exhaust cover bolts (the flat plate between the cylinder heads). And then I would just enjoy the boat!

Congratulations,
fp

 

[MASTER Brian]

Re: Rebuilding Power Head

Ok, I'll re-read the manual about the oil and such. I'm not expecting a huge diffence, but I think it'll keep the bottom end from bogging a bit.

I plan on re-torqueing stuff, cleaning the plugs and double checking fluids in LU and Tilt/Trim.

Thanks again!

 

[KYHunter2]

Re: Rebuilding Power Head

There really isn't going to be any / much difference.

As far as bogging , when you drop back to 50-1.

If the bogging is that noticeable, after breakin and WOT timing check.

You'll need to find the source.

I keep an eye on my plugs during the double oil stage of breakin, and clean them if they start to foul.

This is just MHO, but I use the double oil for the full 10 hours , regardless of fuel use.

Retorque after about 3 hours and 10.

A tip, alot of people , after awhile , when changing plugs , dont use a torque wrench.

Use it, there's alot of posts on here about a loose plug , or one falling out.

Or a stripped plug hole in the head.

Aluminum, can be finicky, one way or the other.

One other thing, your motor has the precision ground caps, the pick isn't alot of help.

The grind marks run horizontal to the break , cant really feel it , just run down the crack.

Hand sanded , are vertical to the break , where you can drag across the crack.

KYHunter

 

[MASTER Brian]

Re: Rebuilding Power Head

I've been using a plug cleaner to clean my plugs after each outing to keep them from being fouled. The 1st time out, there was like I mentioned earlier a lot of gunk built up on them. I'm sure it was from burning off the assembly lube, etc. The last time I checked they were all still a little rich looking, which I'd expect with double oil. The tips were black and wet looking.

I think my flywheel needs to be balanced, I just need to find a place to do it. My machinist said he might if it'll fit on the mandrel he uses for auto, but he didn't think it would. Any suggestions there?

My other thought is maybe the rectifier is going bad. I'm not sure if it would causing some bogging or not, but my tach doesn't seem to be reading 100% accurate all the time. It's been better since the rebuild, but there are times it drops off. I had a lot of wires in the hull of the boat that had been chewed up by something, I figured that was the issue, but it looks like the wire for it is just tied to the ignition key area. That's if some instructions I got were correct. If that's the case, then I don't think that's my problem. I need to find a test for the rectifier and see if it's good.

I plan on re-doing the sync and link 1 more time, to see if anything has changed, but I'd like to take care of that flywheel 1st, so I can cross it off the list. From what I read in Joe's article the low idle timing didn't need to be done, when his method was used, but I think next time I'll do it as well. Mid to high RPM's feel great and the motor sounds excellent at that range, it's the low RPM's that concern me. Idle is fine and if my tach reads it correct about 650 rpms. It just doesn't jump onto plane, like it should. Is there a way to tell if the impeller hub is slipping? Could that be the problem?

 

[KYHunter2]

Re: Rebuilding Power Head

If you mean the prop hub, yes mark the splined area where it goes on prop shaft.


And the area outside the rubber hub , on prop.

After running see if they line up .

If not, it slipping/ spun.

Have you verified timing , running under load?

Why do you think your flywheel needs to be balanced ??

If there's noticeable wobble, that wasn't there before the rebuild.

You need to be sure , something done during rebuild , isn't causing crankshaft movement.

If your rpm's are fluctuating, you need to find the cause NOW.

That with , ( if Im understanding) the flywheel wobble.

Are signs of a serious problem.

KYHunter

 

[MASTER Brian]

Re: Rebuilding Power Head

Do I need to pull the prop to do what you are saying with the prop?

I just wonder if it's not fully engaging at lower speeds and sometimes, when I am trimming the motor up or going through some chop. I checked the prop during the link and sync and the prop seems to lock, just before the carbs open. However, I want to rule any slippage out. I may need to play with shift rod adjustments a tad more, either at the rod or at the linkage and see if I can get it to kick in a little sooner.

I don't really know how to explain why I am wondering about the prop other than low speed seems sluggish, not horrid, just not as hard hitting as it felt before or as I remember it being. Someone has said double oil shouldn't do that, but I'm not so sure that isn't what it is. Maybe I need a new set of plugs. I've been cleaning the ones I have with a spark plug cleaner and figured I replace them after the break-in.

As the RPM's come up around 2000rpms, the boat seems to have great power. Then again when I start trimming the motor up it seems like the RPM's don't climb like they should. They actually do fine, until the motor is about 3/4 of the way trimmed up. Then the trim gauge seems to drop off, even though the motor stays trimmed. I don't think it's the PH, I think it's something else. It's like the boat doesn't want to be at full trim. At this point the PH is purring great and feels very responsive.

I verified timing via the Joe Reeves method and did the link and sync by the book, except inserting Joe's method in place of the RPM test at 5000RPM's minimum. I forget the name of that part.

Should I also run the boat with the tach hooked up? And just go lower speeds?

I think the flywheel needs to be balanced, mainly because I had 3 loose magnets that I re-epoxied down. I did some research on replacing them and saw several things saying to rebalance after replacing magnets or risk wearing out bearings in around 100 hours. I believe I found a shop that will do it for under $50, so I figure I'll have it done, so I'm not worried.

I'm not sure I'd classify it as a wobble, just a minor vibration. I am lacking the support brace bumpers, which came in today. That might even be what I feel. I also might just be imagining that I feel something, because my passangers haven't felt it.

My RPM's aren't fluctuating, my tach just isn't real consistant, meaning when it works, which is more often than not, it's steady according to speed. It's just that sometimes it seems to stop working for a few seconds. Normally at idle it says around 600, but sometimes it doesn't read at all, yet kicks in as I accelerate. Then, if I'm going, say 40mph, it doesn't jump from 4000rpm's to 1000rpm's or anything, it'll stay at 4000, but it doesn't seem to go much beyond maybe 4500, even though my speed increases. Maybe because of the limits of high speed during break-in, it hasn't had a chance to climb any higher. I'm going to test the rectifier to see if that's the issue, then if I don't find it, I may just replace the tach.

Like most boats the onboard speedo isn't real accurate and I keep forgetting to take my GPS out, so I can't get a good gauge on speed vs. RPM's like I'd like to do.

I don't think anything is causing crankshaft movement other than maybe the flywheel, which will be fixed before I take it back out.

Again, a lot of this might just be my imagination being overtly cautious. The more I can rule out the better.

 

[Dhadley]

Re: Rebuilding Power Head

As the RPM's come up around 2000rpms, the boat seems to have great power. Then again when I start trimming the motor up it seems like the RPM's don't climb like they should. They actually do fine, until the motor is about 3/4 of the way trimmed up. Then the trim gauge seems to drop off, even though the motor stays trimmed.

What do you mean by that? Can you elaborate on that?

 

[MASTER Brian]

Re: Rebuilding Power Head

I can try....

Basically, the boat takes a bit longer to get on plain than I would think it should. It seems to lack a bit of low end grunt, that I thought she had prior. It seems like it isn't clearing out as quick as it should at this point. Again, that might be the double oil. To get onto plain, I have the trim down and as it comes onto plain, I start to trim it up.

Again, it's not horrid, just not great. This motor on this boat, should plain out quicker.

Then after she plains out, the RPM's are around 2k, from that point on if I nail the throttle she responds great no noticeable vibration and the motor feels and sounds very strong.

However, if I start to trim up the motor more, to get more top speed out of it, the trim gauge goes to about 3/4 then drops to nothing. That might just be an old gauge, but I don't recall it doing this to this extent prior. At about the time the trim guage drops, it feels as if the boat cavitates a bit or like it's going through some rough water. However, the lakes been relatively calm, a little rough sunday, but nothing horrid, maybe some 1' chop. Saturday was almost glass. If I back off the trim a bit, she stays fine and accelerates.

Prior to the rebuild, I could trim it up to the top line on the gauge, the boat would continue to accelerate without adding throttle. Now it's not as noticeable at least at higher trim levels.

I have one of those hydrafoils on the boat, which was there when I bought it. There was actually a time, I thought, maybe that's coming loose, but it feels snug.

Is that any better? I plan on pulling that flywheel tonight, so maybe I can take her back out in a few days.

 

[KYHunter2]

Re: Rebuilding Power Head

Bryan , its going to be hard for anyone to help .

Unless you get a tach that works correctly and is verified.

When it starts feeling like its cavitating , or rough water.

You may be trimming too much, and starting to lose bite.

Don't depend on the trim guage .

You should be able to feel when the trim is about right.

If it starts to bounce, be hard to handle , and lose speed your over trimmed.

Keep an eye on pressure guage , if you get it trimmed too much , you can start to lose water pressure.


Dhadley, is the man , to help you with set-up.

KYHunter

 

[MASTER Brian]

Re: Rebuilding Power Head

I'm sure you are correct KY. I am going to try to run some electrical tests on it as soon as I can.

Tonight I hope to get the flywheel off so it can get to the shop to be balanced.

I will also crawl under the dash to look at the tach wires.

I don't have a pressure gauge would that be hard to hook up? I suppose I should do a search. I'm guessing they are helpful. It's easy to see the water by pass, so I've been keeping a close eye on it.

Maybe it is getting trimmed up higher than it shows. It used to be a fairly accurate gauge.

I do have a Tiny Tach, if anyone is familiar with those. It's for a 2 cylinder 2 stroke. Basically you ground it and then you wrap the other wire around a spark plug wire. I have used it for several years on a jetski. I wonder if I could hook it to my boat for testing my other tach? Or is it possible to test my tach out to see if it's good as well? I haven't seen any tests in the manual to cover this.

 

[KYHunter2]

Re: Rebuilding Power Head

I believe you can verify your tach, with the tiny tach.

A water pressure guage is one of the best investments you can make.

Its very easy to install.

And will let you monitor water pump operation, as well as condition.

Go to teleflex site , they have all the install info. you'd need.

You can probably buy the guage , right here at iboats.

KYHunter

 

[Dhadley]

Re: Rebuilding Power Head

Ok, it sounds like we have a couple of things happening at once. As you trim up the dial on the trim gauge drops to the bottom line but the motor stays trimmed, right? That's a faulty gauge or a loss of electric / ground. Maybe a bad sender. All of which you already suspect.

The prop starting to vent is a different issue. It just happens to start at the time you lose the gauge. I can't think of a connection between the prop losing bite and the gauge losing signal.

What's interesting is that you say this didn't happen before. And now you have a bad holeshot. Was anything, anything at all, changed about the prop or set up? Prop reconditioned? Motor mounted higher? Lower? Running without the fin now? Battery moved?

 

[funpilot]

Re: Rebuilding Power Head

The only other thing I can think of regarding hole shot is the heat that Wichita is experencing right now, compared to last spring.

I always trim (my much smaller 90) by listening to the engine, and feeling the way the boat (a much lighter aluminum) moves over the water. I may look at my trim gauge, it is pretty consistent. If you are getting a bunch of cavatation, it could be that you are actually trimming higher than you did previously, if something is goofed up with the T and T readout. Check the grounds especially. I'm not sure where that package T and T package mounts on your engine, but you probably removed it during the rebuild. I would remove it again, clean the grounds up, and reinstall.

You can mark the orientation between your hub and the prob blades as KYHunter sugested without removing the prop. Look for your hub, and then note the orientation of the blades. That will tell you if your hub is slipping.

fp

 

[MASTER Brian]

Re: Rebuilding Power Head

KY, I will look into the water pressure gauge. Thanks!

Dhadley, I'll also check the wiring on the Trim gauge. Maybe it got chewed like a lot of other wires and after setting it got worse. I have a wire diagram, so I'll check all fittings. Maybe like fp says, I'm over trimming. I don't think so, but maybe.

As for the prop/LU, the only thing that changed is I replaced the waterpump and have been fighting with the shift rod height. I thought I finally had it, but maybe it's still off a bit. Is that possible? I didn't raise or lower anything that I know of as far as height is concerned. The battery is in the same place and the fin is still on.

Is it possible that my shift height rod is off just a bit? Could this cause the prop issue? Is venting the same as cavitating?

I know some say it's in or it's not, but just before the prop locks in, which is just before the carbs open, the prop catches and releases. It's like it's right on the verge of catching, it just hasn't yet. In my mind it makes sense that if I hit the throttle to go, and the prop is isn't all the way locked in, it would take a minute to go and slip. However, it also makes sense that if there is no grinding and I'm moving forward at idle then it should go, when I hit the throttle.

FP, yeah, it's been hot, but the water temp is in the low 80's. I'll see if I can figure out the prop/hub thing as well.

As for the rest. The flywheel is being balanced, hopefully it's done soon, so I can get going on the link/sync again and see if anything is off. Besides the electrical connections is there anything else I should double check while I'm waiting?

 

[Dhadley]

Re: Rebuilding Power Head

The shift rod height is very straight forward. Been watching the problems you've ran into. Set the height as per the OE manual in neutral and button it up. Once it's set if you still have shifting issues then look at the entire shift system. Make sure the bushings are all in place and not worn. Make sure the cable isn't stretched. Make sure the control works properly.

I notice you keep saying the motor shifts as the carbs start to open, or just slightly before. It's supposed to shift first, fully into gear and then the throttle cable moves. When the throttle cable moves the timing advances slightly and then the carbs start to open. As you advance the throttle the timer base hits the stop and then the carbs continue to open.

It needs to happen in that sequence.

When you shift into gear the lugs on the clutch dog and the gear engage and stay that way. If it isn't completely in gear you'll hear the lugs hitting each other, grinding. If they are engaged but worn or rounded the motor will jump out of gear and then back in with a big bang. Like you hit a log underwater. There won't be any "slipping" like a hydraulic transmission.