93 spi rotary valve damage

[rlw-SD-93spi]

The engine quit and the crankshaft would only turn 1/4 of a revolution. Upon disassembly I discovered that the leading edge of the rotary valve had a 1/8" long cut through the leading edge at 90 degrees from the leading edge. Also the cut edge had been bent in toward the engine block so that the bent/cut edge was hanging up in the front cylinder intake port behind the rotary valve. I can see where the cut edge of the rotary valve has put a small gouge the face of the block at the edge of the front port that I can file smooth, and there is a similar, but more minor scratch in the face of the rotary valve cover at the edge of the hole which abuts the front port which can also be filed smooth. After I removed the rotary valve, the engine rotated freely.

Does anyone know what could have caused this? What should I look for as a possible cause? Can I just reassemble the engine after installing a new rotary valve? This has me completely baffled.

Thanks, in advance, for your help.

[John Kubiak]

Re: 93 spi rotary valve damage

look for missing hardware from the intake silencer all the way to the rotary valve cover. something had to come loose and get in there!

[rlw-SD-93spi]

Re: 93 spi rotary valve damage

Thanks for your prompt reply, John. Believe me I have looked and nothing is apparent. I looked at the piston rods and crankshaft through the intake port last night and the MAG piston rod looks somewhat pinkish in color. The rear piston rod looked more brownish. Upon further rotation, it looks like the MAG piston rod is loose on the crankshaft and has play where the rear piston rod has none at the same point of rotation. It may be that the MAG piston rod and bearing overheated and failed. I think I will have to take the block apart to really see what is going on.

Thanks again,
Ron

[Craig_Canada]

Re: 93 spi rotary valve damage

This happened on the spare engine that came with the boat when I bought it...I was wondering what the heck could have happened there also. Please keep us posted with what you discover. (The engine was in pieces when I bought the boat).

[rlw-SD-93spi]

Re: 93 spi rotary valve damage

John and Craig:
Yes, something came loose. Upon closer inspection I noticed a small brass sleeve pressed into the front oil supply hole on the engine side face of the intake manifold where, on the hull side of the manifold, clear plastic oil lines connect the manifold to the oil pump. I do not know what the sleeves do. The rear sleeve (facing the starboard side) was missing. It looks like when the sleeve came out into the rotary valve space, it was sucked into the intake port and cut in two by the edge of the rotary valve, causing the split and the deformation in the edge of the valve.

Apparently the rear sleeve worked its way out over time because I noticed a small crease in the face of the rotary valve. This restricted oil flow to the front intake port, the front piston rod/crank bearing overheated and blew a 1/4" gap into the spacer that takes up the horizontal play between the rod and the crankshaft.

Questions for tech specialists:
1) Should I remove the brass sleeve from the front oil supply hole in the intake manifold when I overhaul the engine?
2) Can I buy a new rod/crank bearing and spacer and install them, or must I buy the crankshaft/piston rods/bearings as an assembly? My shop manual does not show how to remove the piston rods from the crankshaft, only how to remove the bearings and seals.

Any help you can provide will be greatly appreciated.

Kind Regards, Ron

[Craig_Canada]

Re: 93 spi rotary valve damage

Thanks for posting the result of what you found.

As for the crank shaft, I am about to take my spare crank shaft to a local machine shop and ask them if they can R/R the 1 rod. Something is seized in there, and it looks like everything is press fitted together.

Do you have any pictures of the internal of your engine?

[rlw-SD-93spi]

Re: 93 spi rotary valve damage

Currently no, but I will try to take some and post within the next few days.

[Craig_Canada]

Re: 93 spi rotary valve damage

Ok great, I will too. Were there a bunch of brass shaving in the bottom??? What did your rotary shaft look like? (When I got this one, there were shavings everywhere, but the guy must have threw the old rotary shaft in the garbage because it wasn't in the box of bolts and misc parts. (But there was a brand new one). :D

[rlw-SD-93spi]

Re: 93 spi rotary valve damage

I have not opened the crankcase yet, so there may be additional damage of which I am unaware. I will probably do this during the weekend, since I have a full time day job.

[dsolie]

Re: 93 spi rotary valve damage

That "sleeve" is your oil injection point... I have never seen one come out INTO the rotary area, always seen them fall out (into the hull).

Answers to your q's:

1) You need those sleeves and nipples if you plan on using oil injection. You can plug them or remove them (fill in the holes) if you want to go pre-mix.

2) No.. It takes a special JIG and spacer tools to properly take apart and re-index the crankshafts. Some "shops" can do it without, but not one that I would personally trust with the life of my motor. If you want to buy the parts yourself, you can go to www.wiseco.com and get the con rods and bearings... I would suggest an SBT crank... Core required, and comes with a warranty.

[rlw-SD-93spi]

Re: 93 spi rotary valve damage

Thanks, Dan. Your points are well taken.

I am curious about the relationship between the sleeve and the nipple. I assume that the nipple is used to attach the plastic oil line (I have not taken them off), but how can I get the sleeve back into the hole? Where would I find one? and Would I be able to trust it to not fall out again considering the original did?

Thanks again for your advice.

Ron

[dsolie]

Re: 93 spi rotary valve damage

The sleeve is a press in fit. It comes WITH the nipple attached. And to find one?? no clue. I would assume you would just need to buy a new/used rotary valve cover. How to keep it from happening again? Again.. No clue, as I have never seen these travel INTO the rotary area, and there isn't much room to get creative with JB Weld on the outside surface.

All of mine go pre-mix, as soon as they enter the garage lol.

[rlw-SD-93spi]

Re: 93 spi rotary valve damage

Dan:
If I do go pre-mix will I need to have the rotary valve cover "rebuilt" to re-install the missing brass nipple? Do the parts included in the SBT Oil Pump Block Off Kit allow me to leave the brass nipple missing from one of the oil entry holes without affecting engine function?

[dsolie]

Re: 93 spi rotary valve damage

Ron,

The parts from SBT include vacuum plugs that go over the nipples. Since you have a missing nipple, your best bet is a gob of JB-Weld in it's place and forget the nipple.

[rlw-SD-93spi]

Re: 93 spi rotary valve damage

10-4. Thanks, Dan.