Rotax 787 - 1996 Challenger - 2nd Rebuild Questions

[wernerml]

I am in the process of rebuilding a 787 from my 1996 Challenger. It got put away wet 5 years ago (for a number of sad reasons). It was running ok at that time except stopping engine while in the lake would result in water ingress and hydro locking. I think the water ingress is due to exhaust side issues that will be dealt with as I put it all back together.

My question for the forum has to do with the rotary valve shaft and cylinder bore.

- How easily should the rotary shaft rotate? There is no sign of rust on the rotary like the crank and counter shafts. It turns easy, but doesn't free wheel. The seals on the crank seem to have kept this area water free and there was plenty of injector oil.

- This is the second rebuild, the cylinders are +0.5mm oversize. The SeaDoo shop manual doesn't recommend a second oversize, but some vendors offer up to 2.0mm oversize pistons. I think I could get away with just honing the cylinders and a new set of pistons. Does anyone have any thoughts on boring this again for a +1.0mm over size pistons? These are original OEM cylinders. Planning on new pistons.

I am also in the process of rebuilding the carburetors, replacing fuel lines, changing filters, etc.

Over all this engine probably has fewer than 100 hours of runtime on it, certainly less than 200 and 100% fresh water (Lakes Huron and Michigan mostly)

Unfortunately my mentor, who worked for Kohler, Arctic Cat, and Evenrude for 40 years is no longer available to help me. RIP

Pictures of disassembled crankcase and shaft here - Rotax 787 Seadoo Challenger 1996 - 2nd Rebuild

 

[mikidymac]

The rotary shaft should spin by hand but will not just free spin because of the bearings and seal. If it is apart I would replace the bearings and seal if it was me.

For pistons WSM makes .25, .5, .75 and 1.0 over so I would do 0.75 on yours and bore it to the next size.

 

[wernerml]

Thanks, I am going to get 0.75 mm oversize top end kit from WSM. On further inspection I am going to not do anything with the rotary shaft at this point. Time to start adding up the $$

Now looking for a machine shop here in SW Michigan. I have a lead on one that I need to go visit. Anyone have any recommendations?

 

[wernerml]

Thanks for all the help here and all around this great forum! I learned a lot of things even without asking new questions.

I started my engine today idled fine for 10 seconds then I shut it down as I didn't have any water connected. I had pulled fuel into the carbs using a siphon pump on the return line. Only had to crank for about 20 seconds and pull the choke a bit.

The machine shop talked me into going up to 1.0mm oversize. He was concerned that an 0.25mm increase wouldn't give him enough elbow room to do a good job. Looked good when I got them back. I also didn't rebuild the rotary shaft. I did a thorough inspection and it looked good. Being submerged in oil seems to have kept any water out. It has been about 8 years since it was rebuilt, but it probably only has about 30~40 running hours on it.

Time to re-install the jet pump hook up the last water line and head to the lake before the water gets hard.

Weather forecast says 79 degrees Monday! Being retired has its advantages.