Engine high speed RPM problem

[fzandome]

Ok, have the cylinders off the eng and the piston was shot... Wondered why it still turned over. Anyway what does the pressure check involve and if the seal is leaking, do I need to split the case.... Getting interesting now. Glad it's fall to be digging into it this far.


Read up on the leak down check and now that the cylinders are off there is no way I can do this now. So the question remains do I have to crack the case to replace this front seal. If so, I might as well get a new engine than to fix this 20 year old motor.... FOR SALE, slightly used boat... needs new engine.... LOL

 

[Mekanix]

Nah "just needs a starter"

The pto seal has a ring holding the seal in and the mag side is just squished in place but could be replaced with persistence. But if your going that far might as well split the case.

 

[Sportster-2001-951C-Stock]

Was there any oil in the bottom of the crankcase? The oil puddle should at least touch the crank wheels

Also, check the MAG oil injection nozzle and see if it's clogged.

If that roasted piston spread shrapnel in your crank bearings then you'll have to split the case. Did you find aluminum particle contamination in the lower crankcase? If so, the bearings are contaminated.

 

[fzandome]

There was oil in the bottom cases. when I spin crankshaft they come up wet.
There are particles in the bottom case. so the case have to be split to clean, If I decide to do this, other that cleaning out the oil and the case what do I do about the main bearings.. clean or replace. Also, while it's that far apart what else should I focus on...

I did an analysis of the piston damage based on photos I found on the internet.. Damage was primarily on the exhaust side with piston scuffing on that side. Photos indicate a lean condition and one of the "causes" was crankcase seal leak. So I am not going to put in a top end and have this problem again in the near future. So a definite case split or eng replacement in the works.

Off topic. saw some, not a lot, of very small gravel in the water chamber on the PTO cylinder. Can this clog anything down stream on the discharge side??? Should I check the water jacket on the other eng???

 

[Upallnight]

Oh no, that's not good... My first thought was the crankshaft might be twisted and caused the cylinder to fire too early before top dead center, or perhaps the flywheel key is sheared, but this would also be the case for the PTO as well (firing the fuel charge out of time, ie: too early).

Now I'm thinking you must have a leaking outer crankshaft seal causing a lean cylinder, specifically the crank seal under the MAG flywheel.

So best case the motor should be leak checked to confirm the seal is leaking, replace the crankshaft seal and repair the cylinder or perhaps go with a reman engine exchange with no fault warranty.

I dunno why earlier we didn't consider your crank seals might be damaged.....

EDIT: As far as confirming lubrication goes, you can confirm the oil injection nozzle is not clogged on the MAG cylinder.

Also, if there's ever any question about cylinder/crankcase lubrication then oil can be added manually either by mixing with the fuel or even temporarily by squirting some into the carburetor.

Is there any problem with using the oil injection system and premixing a little oil with the gas?

Previous owner(s) installed a SBT engine in the boat and went with premix, however they never disconnected any of the lines and just empty out the oil tank. SBT didn't inform them that they need to keep oil in the lower case for the rotary gear and bearings.

I rebuilt the engine when I was having problem with the engine (was a broken woodruff key on the flywheel) that was messing up the timing. I checked the oil pump when I had the engine apart and replace the oil lines. I ran premix 40:1 with the first 5 gal. of gas but have been running straight gas with no premix once I saw that the oil lines were filled with oil.

I might go with a 60:1 premix mixture just to be safe.

 

[Sportster-2001-951C-Stock]

Is there any problem with using the oil injection system and premixing a little oil with the gas?

Previous owner(s) installed a SBT engine in the boat and went with premix, however they never disconnected any of the lines and just empty out the oil tank. SBT didn't inform them that they need to keep oil in the lower case for the rotary gear and bearings.

I rebuilt the engine when I was having problem with the engine (was a broken woodruff key on the flywheel) that was messing up the timing. I checked the oil pump when I had the engine apart and replace the oil lines. I ran premix 40:1 with the first 5 gal. of gas but have been running straight gas with no premix once I saw that the oil lines were filled with oil.

I might go with a 60:1 premix mixture just to be safe.

In the case of a carbed motor such as this one, the fuel can be pre-mixed in addition to using the oil injection system but to go off injection completely the carb really should be rejetted richer by the percentage of the oil ratio. Does anyone ever do that? Well, not many do, they just mix and go.

The rotary valve motors need to have and oil bath maintained in the RV drive gear box, so at least make sure if your motor uses an rotary valve industion that gear box always has oil in it while the engine is running or else the gears that drive the valve will be damaged.

Adding some amount of oil to the fuel in addition to using the oil injection system adds expense to operating costs and is unnecessary if the oil injection system is properly maintained, such as adjusting the control cable properly and checking it, also the oil lines tend to rot and crack over a decade of use along with the oil can congeal inside the nozzles, the oil strainer should be replaced probably every few seasons as well.

So my feeling is, the variable ratio oil injection system is quite robust and it's worth the trouble of keeping it maintained b/c it will save you money over pre-mixing due to lower operating costs.

It's quite common to dump some oil mixed with fuel into the fuel tank if there's a reason to believe the oil injection system might be malfunctioning, such as for instance it was just serviced and may not have been purged of all air bubbles or the control cable was accidentally broken somehow, or for whatever other reasons it's okay to add some oil to the fuel temporarily until the oil injection system is repaired and proven functional.

If for instance I had just replaced my motor and of course this means the oil injection system was also just reassembled thus might not function properly, then I wouldn't hesitate to add oil to my fuel until I had the opportunity to test the oil injection system for proper function and make sure all of the air bubbles had been completely purged from the system.

One way to test the system is by with engine running on pre-mix pulling the cable to open the injection pump valve about 60% of normal travel while fast-idling and watch to confirm the system delivers a ton of oil (smoke in the exhaust).

 

[Sportster-2001-951C-Stock]

There was oil in the bottom cases. when I spin crankshaft they come up wet.
There are particles in the bottom case. so the case have to be split to clean, If I decide to do this, other that cleaning out the oil and the case what do I do about the main bearings.. clean or replace. Also, while it's that far apart what else should I focus on...

I did an analysis of the piston damage based on photos I found on the internet.. Damage was primarily on the exhaust side with piston scuffing on that side. Photos indicate a lean condition and one of the "causes" was crankcase seal leak. So I am not going to put in a top end and have this problem again in the near future. So a definite case split or eng replacement in the works.

Off topic. saw some, not a lot, of very small gravel in the water chamber on the PTO cylinder. Can this clog anything down stream on the discharge side??? Should I check the water jacket on the other eng???

I agree, IMO this engine needs to come out of the boat if the repair is going to last any period of time.

If there was aluminum from the piston flying around in the crankcase with the crankshaft, this has probably caused damage to the crankshaft and rod bearings, I'd be hard-pressed to trust this rebuild if it excluded a replacement crankshaft and depending on the motor if it has a balance shaft I'd want new bearings there too.

As far as the gravel goes, a small amount is not likely to have a dramatic impact as long as the water flow isn't being blocked but I've seen several ski engines just full of sand that would overheat in a matter of minutes, reverse flushing some of these didn't help as they were just too full, tried flipping them upside down and flushing that way even and still couldn't get enough out. I'm quite sure these were victims of abuse, it must've been fun for someone to watch as the jet pumps sucked up a sand bar and spit it up into the air?

 

[fzandome]

The engine is now out of the boat and packaged for overhaul. Will post again when it's in and running. Thanks for all the information and discussion. I learned a lot. Now if the other engine stays up for another year, I'll be happy.

 

[Sportster-2001-951C-Stock]

Good job. This one fooled me from the beginning I think b/c leaky crank seals usually cause an unstable idle.

 

[Bonmotwang]

Ok, have the cylinders off the eng and the piston was shot... Wondered why it still turned over. Anyway what does the pressure check involve and if the seal is leaking, do I need to split the case.... Getting interesting now. Glad it's fall to be digging into it this far.
View attachment 27637View attachment 27638

Read up on the leak down check and now that the cylinders are off there is no way I can do this now. So the question remains do I have to crack the case to replace this front seal. If so, I might as well get a new engine than to fix this 20 year old motor.... FOR SALE, slightly used boat... needs new engine.... LOL

Wow. Engine was able to run before piston reached this stage?


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[fzandome]

The new engine was installed and I did about 2 hours on the lake yesterday. Still have to do some fine tuning on the carbs but will get to that next run. Water is coming in while I'm at speed but could not look into the eng compartment while driving to find out where. Need a second person to drive and EAR PROTECTORS before I can do that. Almost ready for the summer. It was quite a learning experience.