predator hemi mudmotor build - break in hot case?

[cobob]

First, thanks for all the great info. This forum has been my no. 1 source for info for this project, and i had minimal experience in 4-stroke small motos before this.

I have built a hemi 212 for use on a mudmotor and have a few questions i can't seem to find answered in searches, and I am open to any suggestions for this project. The goals are low-RPM, high torque, reliability.

Currently installed:
bored .625 honda carb
NR open intake filter & cheep-o breather filter
Robertson torque tube loop header with RVL muffler
NR 280-211 cam :devil2:
MILDLY ported and hand-polished head - DIY
.010 stainless head gasket
removed governor and low oil sensor
4 deg. timing key
18lb springs


waiting for tuning:
140 emulsion tube
various jets
fancy sparkplug
???


initial questions are:
- How hot is this crank case supposed to get? It seemed to get real hot in the fort 20 min break-in run, but i'm not sure if its just in my head. Seemed hotter then the dirtbike crank cases i'm used to dealing with (over 10 years ago). Checked plug; does not look lean.

- How can i quiet down this RLV muffler? all searches lead to steelwool, and i'm over the water so sparks are not a concern. Just wondering if there is a better option.

- I know my weak point in the rod and flywheel; will the honda GX flyweel work on the predator 60363? i need to keep a high mass flywheel for chewing through stuff on the river. Max RPM should not go over 5K - as soon as i see 5K i am at least replacing the rod.


any other recommendations for low rpm torque? break-in? I have a break in additive in the oil and will switch to synthetic after the first change

thanks all.

 

[cobob]

Paint cooked off the header during the second run. Is this normal? Case is hot to the touch

 

[cobob]

3rd run went well, not as hot, drained the oil and it smelt a little burnt. Plug still looks good, checked flywheel and timing key and the key looked warn weird, flywheel may have slipped some.

Going to order a new 4 degree key and gaskets, will send a 8 degree key and a used plug to anyone who can tell me if the honda flywheel will fit this motor. Thanks

 

[65ShelbyClone]

If the flywheel slips, the timing will retard and make the exhaust temp go WAY up....enough to burn off header paint. Since your engine is in a boat and will see high load conditions a lot, I would be conservative with an advanced key.

As for case/oil temps, can't really tell anything without an actual number or symptoms of it being too high. A photo of the plug coloring would help.

And no, a GX200 flywheel will not fit a hemi Predator. They use one interchangeable with a Kohler CH270 for some strange, yet distinctly Chinese reason.