Repower an 1872 with a CH18S
 

Hi all,

I have an 1872 with a very tired engine and I have decided to replace the M18 with a CH18S. I did some research here and picked up an 1863 for the engine and other parts. The 1863 has about 700 hours on the meter and seems to run great. Just looking for you folks to look over my shoulder to check my plan.

Use the 1863 engine mounting plate to locate the front PTO.
The 1863 engine will have the correct muffler and heat shield to use in the 1872.
Will need to add an air duct on the flywheel side to stop recirculating hot air for cooling.
Front PTO pulley on the CH18 is larger (6" I think) and I will need to use the PTO from the 1872 or get a new PTO with 4.5" pulley.
May need to modify the air cleaner cover to clear the firewall.

Parts I am not as sure on:
Driveshaft, use the 1863 shaft as it currently connects to the CH18 and upgrade the pump side to eliminate the rag joint style. To do this I would need an adapter and a user here, JeffinPA, sells those. Then I would need to lengthen the driveshaft. I am thinking a short piece of tube with the correct ID and cut/sleeve/weld the 1863 shaft to the needed length.

Wiring: current setup shuts off by grounding the coil, I still need to do some research to make sure that will work on the new ignition system.
Find a circuit that will energize the fuel valve on the carb. I have not figured this out yet but hoping there is a leg of the charging circuit that is hot in the run position only. What have others used?
I think there is an oil sentry system on the CH18, was wondering if that was worth retaining?
Need to look into how to hook up the oil pressure light currently in the 1872. Is there a pressure switch on the CH18 that will work?

Any other conversion issues to consider that I have missed? Any other parts from the 1863 that will swap over to the 1872 that I should consider such as the mule drive?

While the engine is out I am going to make sure all the fins are clean. I gave it a full tuneup and oil change and have been using the 1863 for a few hours now and don't see any leaks or other issues. Is there anything else I should do to it while it is out? Head gaskets, de-carbon, etc...?

Thanks, and sorry if some of this stuff has been covered. I feel like I have started to go round in circles with my searches here.

Hi bleoh,
I currently did the same swap in my 1872. I put in a ch 20 from a cub 2206 in the 1872. I can share some of the things I have done. I have only had it running for about an hour total. I still have to make a heat shield and get a xtreme pto for it.
Seth

I have not had a bunch of time to work on it, but I have got a little bit done. The wiring is not that hard, once I found good wiring diagrams for both it was fairly easy. I pulled the solenoid wire from the rear of the 1872 up to the front since the solenoid is on the CH18 starter vs in the rear by the battery on the 1872. I used the engine side harness from the M18 and the chassis harness from the 1863 to make a sort of patch harness to go from the new engine to the 1872 chassis.

For the "firewall" I am going to use the one from the 1863 and just trim it off where it meets up with the curved section of the 1872's firewall.

for the throttle cable I used the one from the 1863, it is on the opposite side of the dash between the two models, but the mounting holes lined up fine. I just had to mount the plastic handle upside down so it did not hit the steering column on the 1872. I moved the choke from the left side to the right so it would reach. I used an existing hole for a switch and just used washers to take up the gap in the bigger hole.

I will say it has been nice having the whole 1863 there to pull parts from.

Here are some pictures.

old engine getting ready to come out. I have re-attached that end cap on the muffler a couple of times, but the occasional backfire is hard on it!
https://i.imgur.com/XOOyqMEl.jpg

M18 is out
https://i.imgur.com/aiO80gVl.jpg

CH18s from the 1863 is out
https://i.imgur.com/xoH3Mecl.jpg

I make the CV adapters that you need. I can also lengthen the driveshaft for you. Although the "slip it into a piece a tube" would work, any runout will cause premature wear. I cut the driveshaft on my lathe and make a "pin and reamed hole" to minimize runout. I have plenty of driveshaft material drops from shortening other driveshaft to lengthen yours. After TIG welding the driveshaft, I verify it's still concentric ( straight )

Jeff

Jeff from PA, I also in need of a driveshaft to mate an 1863 engine to an 1872, how do I go about making this happen? New to forum…

You can contact Jeff by the link {banner} at the top of the home page.
Good guy to do business with.

Ken

PM sent......

A drive shaft from a 2084 or a 2284 will bolt in as long as you have a CV style pump adapter on the pump.