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Cushman Scooter Engine Rebuild

dkirk

Registered
Here's my wintertime project - freshening up this Cushman scooter engine. A good friend bought the scooter which he is restoring and I volunteered to do the engine. After pulling the flywheel and getting spark restored (points needed cleaning), it started right up and ran fairly well but quite a bit of blue smoke in the exhaust. After head removal I can see why...cylinder walls glazed and piston a bit loose in the bore. Valves have excessive play in the guides so this engine will get a total overhaul - next size overbore with new piston and rings, plus new valve guides and maybe new valves - we'll see how things look as project progresses.

These are really neat, well designed and heavy duty engines. With a 3.0" bore and 2.75" stroke, displacement is 19.4 cu in. Does anyone know the rated power on this model?
 

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Joseph Cissell

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Last Subscription Date
01/07/2017
Pretty sure you have a 8 HP Husky there. :brows:
Doug, You have a 7.95HP Husky Cushman Engine. They called them a 8 HP Engine. Cushman made their own engines and they were good engines. They could have used a better Carb, but that one worked, but not real good. Some states would not let you buy a Cushman Eagle Scooter with the 8 HP engine on them. You had to order a 5 HP Cushman Engine from the factory on your new Cushman Eagle if you lived in one of those states. Thanks, Joe
 

Marv in Minn

Subscriber
Last Subscription Date
02/05/2020
Doug, You have a 7.95HP Husky Cushman Engine. They called them a 8 HP Engine. Cushman made their own engines and they were good engines. They could have used a better Carb, but that one worked, but not real good. Some states would not let you buy a Cushman Eagle Scooter with the 8 HP engine on them. You had to order a 5 HP Cushman Engine from the factory on your new Cushman Eagle if you lived in one of those states. Thanks, Joe
also if the operator was under 16 yr old. that engine has a rounded cylinder.
i have both scooters, top speed of the 5hp is about 40 on level ground.
i have a dickens of a time keeping up on a Cushman group run with that one. :O
 

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Doug Oldenburg

Subscriber
Age
72
Last Subscription Date
07/02/2019
Doug, You have a 7.95HP Husky Cushman Engine. They called them a 8 HP Engine. Cushman made their own engines and they were good engines. They could have used a better Carb, but that one worked, but not real good. Some states would not let you buy a Cushman Eagle Scooter with the 8 HP engine on them. You had to order a 5 HP Cushman Engine from the factory on your new Cushman Eagle if you lived in one of those states. Thanks, Joe
I was responding to the question asked at the top. I do not own the engine in question here, though I do own several Cushman scooters. I am aware that the engine in question is not an actual full 8 HP, but it is commonly referred to as an 8 HP. I do agree on the carb. & in the past have replaced it with a Carter mod. N, with the round bottom float bowl & that worked somewhat better for me.
 

dkirk

Registered
Thank you gentlemen for your information and comments - much appreciated.

I'm progressing on the Cushman overhaul, working on it when time allows. Enjoying the fact that I have all winter to rebuild it so no pressure - I can enjoy all facets of the job.

Got the piston dome scraped and see that it's marked .002 as well as on the block deck. This must have been factory markings - a commonly done procedure when a bore turns out slightly oversize during manufacture.

Flywheel and stator were removed and all coils visually appear good - no sign of overheating on the lighting coils. As previously stated, I ran the engine thus confirming that the ignition coil, points and condenser are working.
 

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ramsay

Registered
also if the operator was under 16 yr old. that engine has a rounded cylinder.
i have both scooters, top speed of the 5hp is about 40 on level ground.
i have a dickens of a time keeping up on a Cushman group run with that one. :O
I had a 1958 Eagle with 3" bore when I was 15 I think.. That was many years ago.. I remember I had Pope's bore the cylinder and I overhauled the engine... I am 67 now... Mike in Louisiana
 

dkirk

Registered
Now that the holidays are over with, I'm back on the Cushman. Got the base plate removed and there was about 1/4" thick black sludge on the bottom. The previous owner was obviously not very good at changing the oil. Oil pump screen was still clear so engine was still being lubricated. The sludge was so viscous that I had to use a putty knife to remove it. Looking into the crankcase, other than a black coating on everything, all parts looked good. I'm impressed with the 4 stud/locknut rod cap on the forged steel rod...quite heavy duty. After removing the piston and rod assembly, I was happy to see that the piston skirt looked worn, but no score marks. Also the crankpin bearing, which is the removable shell-type, looked perfectly serviceable with no score marks or embedded metal. All of this indicates that the engine was never run low on oil. Will start measuring up parts when disassembly is complete.
 

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dkirk

Registered
Got the Cushman engine totally disassembled now. Only surprise was the wrist pin bushing in the connecting rod - it was loose and fell out of the rod when the pin was removed. I think oversize OD bushings are available from Carpenter. The bare block is now ready for ultrasonic cleaning and boring .010 over.
 

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dkirk

Registered
Ed,

Good thought but the overhaul manual states that it is a light press fit. I was able to obtain the .003 oversize OD bushing from Dennis Carpenter that should fix this. Pounding out of this bearing on Cushman engines is somewhat of a common problem I've heard.

My order of $225.00 in parts arrived from Carpenter. Most parts are labeled "Made In China" but seem to be of high quality. I'm replacing lifters, springs, valve guides, valves, crankshaft seals, both con rod bearings, along with a .010 over piston and rings. Gasket set is included, plus an oil pump rebuild kit.

First thing to get rebuilt was the oil pump. After washing away sludge, especially in the pick-up screen, pump was immaculately cleaned in mineral spirits and fitted with 2 new springs and check balls. Pumps very nicely now, as tested manually in a pan of light oil. Tomorrow the block goes to the machine shop for re-bore and hone, plus valve guide install and valve seats cut.
 

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BradH

Registered
Ed,

Good thought but the overhaul manual states that it is a light press fit. I was able to obtain the .003 oversize OD bushing from Dennis Carpenter that should fix this. Pounding out of this bearing on Cushman engines is somewhat of a common problem I've heard.

My order of $225.00 in parts arrived from Carpenter. Most parts are labeled "Made In China" but seem to be of high quality. I'm replacing lifters, springs, valve guides, valves, crankshaft seals, both con rod bearings, along with a .010 over piston and rings. Gasket set is included, plus an oil pump rebuild kit.

First thing to get rebuilt was the oil pump. After washing away sludge, especially in the pick-up screen, pump was immaculately cleaned in mineral spirits and fitted with 2 new springs and check balls. Pumps very nicely now, as tested manually in a pan of light oil. Tomorrow the block goes to the machine shop for re-bore and hone, plus valve guide install and valve seats cut.
I am also doing a rebuild on my oil pump on my 58 Cushman Husky 5hp..... How was you able to get the circlip off to remove the pump?.. I am not having any luck popping this off and wonder how you did this? I only have access thru the bottom plate.
 
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dkirk

Registered
I am also doing a rebuild on my oil pump on my 58 Cushman Husky 5hp..... How was you able to get the circlip off to remove the pump?.. I am not having any luck popping this off and wonder how you did this? I only have access thru the bottom plate.
Brad - The oil pump was the last thing I removed, after removing the side plate, crankshaft and camshaft. I also struggled with that retaining ring through the bottom and didn't have any luck. Going in through the side is easy - ring is totally accessible.
 

dkirk

Registered
My Cushman engine block is still at the automotive machine shop. Bore did not clean up at a .010 oversize from standard, so I had to order another piston and ring set at .020 over. This engine was really worn out! Should have the block back next week and start reassembly.
 

dkirk

Registered
Finally got parts back from the machine shop. Block was acid-dipped and is now immaculately clean - looks like a brand-new casting. The .020 bore is right to spec with a beautiful cross-hatch. New bronze guides installed and valve seats cut.
 

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dkirk

Registered
The crankpin was found to have a flat spot around the 12 o'clock position, probably due to pounding from the worn-out wrist pin bearing (see earlier post). As there are no undersize rod bearings available, I had the crankpin spray-welded and reground back to standard diameter. It turned out very nice and the wear surface is harder than the original nodular iron. The connecting rod is now fitted with the replacement wrist pin bronze bushing and was reamed to fit the pin perfectly. Now I can enjoy assembling this clean engine with all parts to spec.
 

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Dick DeBuse

Registered
Undersize rod bearings are available in .010 .020 .030 .040 .050, and maybe .060 from Carpenter. There are also a lot of NOS out there. NOS Cushman parts usually go for about 20% under Carpenter's prices. The new Carpenter online catalog lists the undersizes separately on another page.
 

dkirk

Registered
Dick,

Thank you for the information on rod bearings - I did not know that Carpenter offered undersized bearings as I ordered parts off of their website and there they only list the standard size bearing.

I measured up ring end gaps in the bore with the new .020 oversize rings and recorded the following:

Top compression ring - .012
Second compression ring - .016
Oil control ring - .010

The Cushman shop manual states a range for all ring end gaps....017 to .025. This sounds excessive to me. A comparable Kohler K-series engine (3.0 in bore) has a manual spec of .007 to .017, with a high limit of .027. Thus, I am going to fit rings right out of the box, without adjusting end gap clearance. The top ring gap of .012 seems well within the Kohler spec, and the .016 gap on the second ring is desirable as a larger clearance here (compared to the top ring) allows for better oil control. Piston is now fitted to rod and rings are installed. Making progress.IMG_1702.jpg
 

dkirk

Registered
Back on the Cushman - acid dipping the crankshaft for cleaning dissolved the aluminum oil slinger. Have a new one fitted up with rivets Loctited in place. Bought a new camshaft as the original was very worn.

First step in the assembly was getting the rebuilt oil pump fitted back into the block.
 

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dkirk

Registered
Cushman work being resumed on this rainy Sunday. I didn't like that felt seal on the PTO side of the engine, so I purchased this seal adapter from Dennis Carpenter. It allows the flywheel side lip seal to be used on the PTO side. Installation of the adapter and seal was straightforward.
 

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