Cam, Timing, and Rocker Ratio for Low RPM torque build HEMI mud motor
More work...
Got some go fast parts from Small Engine Cams.
Got the governor out, the oil sensor out, plugged the governor hole (1/4-20) and the oil sensor cable hole (7/16-20). Replaced the rod with the ARC billet, and the cam with the Black Mamba Jr. Buttoned up the case with a new gasket.
Waiting on a timing light so I can verify the timing, but right now my dial wheel says 34° BTDC. I'm going to run without a key and try a range from 26° to 32° to see where I get the best power at lower RPM.
Starting making an adaptor for the Mikuni Clone VM22 carb.
I matched the motor side port to the intake port. I need to assemble it to the engine to line up the VM22 to make sure it sits level before I cut the flange for the Mikuni.
I also started on a custom header. Tube bending is not my forte.
Time is my enemy....
BWL - sorry to hear about your tragedy. That would suck if you were far from the ramp. Furthest I'll be is about 2 miles, but that would be a hell of a paddle!
Got some go fast parts from Small Engine Cams.
Got the governor out, the oil sensor out, plugged the governor hole (1/4-20) and the oil sensor cable hole (7/16-20). Replaced the rod with the ARC billet, and the cam with the Black Mamba Jr. Buttoned up the case with a new gasket.
Waiting on a timing light so I can verify the timing, but right now my dial wheel says 34° BTDC. I'm going to run without a key and try a range from 26° to 32° to see where I get the best power at lower RPM.
Starting making an adaptor for the Mikuni Clone VM22 carb.
I matched the motor side port to the intake port. I need to assemble it to the engine to line up the VM22 to make sure it sits level before I cut the flange for the Mikuni.
I also started on a custom header. Tube bending is not my forte.
Time is my enemy....
BWL - sorry to hear about your tragedy. That would suck if you were far from the ramp. Furthest I'll be is about 2 miles, but that would be a hell of a paddle!
Yup, that's why I have oars, and a paddle to back that up. I'd recommend not holding at high rpm for very long. 6k - 7k for maybe a mile at a time, then let the motor cool down. Think like a drag racer or a standing mile racer. Do a quick run, let it cool down then go for another run.
Hey, let me know what you end up doing for a header. Mud motor guys are always looking for new header designs since we need more torque than anything. I had a guy on Ebay make mine.
See i never got my timing perfect either. I was trying to get better rockers and valve train, then I was going to get the timing perfectly over the weekend or something. The hemi has better rocker anyway right?
Hey, let me know what you end up doing for a header. Mud motor guys are always looking for new header designs since we need more torque than anything. I had a guy on Ebay make mine.
See i never got my timing perfect either. I was trying to get better rockers and valve train, then I was going to get the timing perfectly over the weekend or something. The hemi has better rocker anyway right?
Timing
Well my eBay timing light arrived. Hooked it up and spun the motor with a cordless drill.....nothing. Dead. Ugh. So I bought another one through Craigslist. Guy demonstrated that it worked on his car. (my car is a Subaru with no access to the plug wires). Anyway get it home and no dice. Light would not strobe. Hmm... Then I replaced stock flywheel with the ARC wheel thinking it might have hotter spark. Nope. Then I hooked up my spark plug gap tester and tried grounding the lead. Nope. Set it for max opening that spark could jump. Nope. Then started dialing it back, and what do ya know? A gap of about .25" is just right for the timing light to pick up....OK, back in action.
I found TDC with a dial gage directly on the piston center (head is still off), and set a timing wheel to TDC using a piece of wire for the indicator. Then checked where on the rotation the flywheel was when it sparked. 33°BTDC for the ARC wheel when using the key. These pics are with the motor cranking at around 1200rpm, and are actual timing light reads.
I measured the stock flywheel timing as 25°BTDC.
Wanting more low end power, and not in need of over 6k rpm, I set it to 28°BTDC without a key. Took a few tries while tightening the nut to get it just right...
So then I needed a way to torque the flywheel nut. Here is my locking bar.
Just some mild steel with a 3/4" hole drilled in and some welded tabs. Works great. No marks left on shaft.
OK, still have to finish carb adaptor and header then we can fire this puppy up and see what we get....hopefully not a broken case! To that end, my mud motor does not direct drive the shaft with the housing attached to the motor. The motor is mounted to a frame and is coupled to the prop shaft with a CV joint (from a Polaris ATV) so the long shaft should not stress the motor casing (much).
Well my eBay timing light arrived. Hooked it up and spun the motor with a cordless drill.....nothing. Dead. Ugh. So I bought another one through Craigslist. Guy demonstrated that it worked on his car. (my car is a Subaru with no access to the plug wires). Anyway get it home and no dice. Light would not strobe. Hmm... Then I replaced stock flywheel with the ARC wheel thinking it might have hotter spark. Nope. Then I hooked up my spark plug gap tester and tried grounding the lead. Nope. Set it for max opening that spark could jump. Nope. Then started dialing it back, and what do ya know? A gap of about .25" is just right for the timing light to pick up....OK, back in action.
I found TDC with a dial gage directly on the piston center (head is still off), and set a timing wheel to TDC using a piece of wire for the indicator. Then checked where on the rotation the flywheel was when it sparked. 33°BTDC for the ARC wheel when using the key. These pics are with the motor cranking at around 1200rpm, and are actual timing light reads.
I measured the stock flywheel timing as 25°BTDC.
Wanting more low end power, and not in need of over 6k rpm, I set it to 28°BTDC without a key. Took a few tries while tightening the nut to get it just right...
So then I needed a way to torque the flywheel nut. Here is my locking bar.
Just some mild steel with a 3/4" hole drilled in and some welded tabs. Works great. No marks left on shaft.
OK, still have to finish carb adaptor and header then we can fire this puppy up and see what we get....hopefully not a broken case! To that end, my mud motor does not direct drive the shaft with the housing attached to the motor. The motor is mounted to a frame and is coupled to the prop shaft with a CV joint (from a Polaris ATV) so the long shaft should not stress the motor casing (much).
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Actually my long shaft doesn't stress the casing much either. Only 10 - 12 lbs/ft on the bolts and the water supports the weight of the shaft while running because the propeller generates lift., and the design has been around for about 50 year. There's an entire country of people who make a living fishing with these motors everyday. The casing never failed for the two years I near it stock/stage1. If the main stress was on the side plate, that's where the failure should have happened. The long shaft on the side plate wasn't the problem.
My motor mounts on a frame and has a coupling as well.
Thin casing is thin casing. I'm done with HF.
I prefer the long shaft because fewer transmission losses, but I've never run anything else. Also the direct shaft has fewer moving, and the longer shaft gives a better angle to the water compared to the beaver tails.
My motor mounts on a frame and has a coupling as well.
Thin casing is thin casing. I'm done with HF.
I prefer the long shaft because fewer transmission losses, but I've never run anything else. Also the direct shaft has fewer moving, and the longer shaft gives a better angle to the water compared to the beaver tails.
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School me on valves
I picked up split keepers intending to install them with the stock valves. These will not work together. So either I run with the stock retainers and eat the $20 cost of the split keepers and aluminum retainers, or I buy aftermarket stainless valves for an additional $40.
What are the advantages of the stainless valves, other than the split keepers?
If I buy the stainless valves, do I need to cut the seats? Or can I just lap them into place?
The valves available from NRRacing are +.050" valves. Why would I want +.050" length?
OldMiniBikes does not list individual valves for the hemi (27mm/25mm)
Smallenginecams.com does not say anything about the length...
Thanks
I picked up split keepers intending to install them with the stock valves. These will not work together. So either I run with the stock retainers and eat the $20 cost of the split keepers and aluminum retainers, or I buy aftermarket stainless valves for an additional $40.
What are the advantages of the stainless valves, other than the split keepers?
If I buy the stainless valves, do I need to cut the seats? Or can I just lap them into place?
The valves available from NRRacing are +.050" valves. Why would I want +.050" length?
OldMiniBikes does not list individual valves for the hemi (27mm/25mm)
Smallenginecams.com does not say anything about the length...
Thanks
Valves...
New stainless valves are on order.
Supposed to flow better, be lighter, and use the split keepers and aluminum retainer.
Figured out the + 0.050" does not "open more" but rather allows the valve to open more before the spring reaches full stack height IF you have a very large cam.
Valve only opens as far as the cam and rocker ratio force it to regardless of the valve length. The extra 0.050" just allows you to run a larger cam without binding.
My Mamba Jr is .275", so still pretty conservative. The extra .050" will just be taken out with the lash adjusters.
New stainless valves are on order.
Supposed to flow better, be lighter, and use the split keepers and aluminum retainer.
Figured out the + 0.050" does not "open more" but rather allows the valve to open more before the spring reaches full stack height IF you have a very large cam.
Valve only opens as far as the cam and rocker ratio force it to regardless of the valve length. The extra 0.050" just allows you to run a larger cam without binding.
My Mamba Jr is .275", so still pretty conservative. The extra .050" will just be taken out with the lash adjusters.
More progress...
I finished the Mikuni VM22 carb adaptor. I wanted to keep it short to keep the carb out of my way and I read (believe everything on internet?) that a longer runner promotes velocity which in turn is good for high RPM. So shorter logically would be better for lower RPM? Anyway... The intake side is matched to the head opening, while the carb side is matched to the 25mm opening of the VM22. The transition is smooth between the two, like a porting job I left it at 80grit.
I also added electric start to my Predator 212 Hemi. I bought a billet ring gear ($70) from ARC Racing they make for the GX200. I had to trim the thickness to fit in the offset between my ARC billet flywheel and the motor. Even after trimming, I still had to relieve about .020" off the casing to give adequate clearance. I clamped the ring to the flywheel and used a dial indicator to make sure they were concentric (to within .003", but ring gear was not perfectly round...). I then match drilled the ring to the flywheel, tapped the holes, c'sinked the mounting holes and used flat head screws with red Loctite. The starter is a GX200 Chinese knockoff bought on eBay for $23. No charge coils, but that's fine, I have a large marine battery in my boat.
In my conversations with ARC, they let me know they make an electric start flywheel for the HEMI. P/N 6686 and cost is $220. Not listed on their site, and is a special order.
I finished the Mikuni VM22 carb adaptor. I wanted to keep it short to keep the carb out of my way and I read (believe everything on internet?) that a longer runner promotes velocity which in turn is good for high RPM. So shorter logically would be better for lower RPM? Anyway... The intake side is matched to the head opening, while the carb side is matched to the 25mm opening of the VM22. The transition is smooth between the two, like a porting job I left it at 80grit.
I also added electric start to my Predator 212 Hemi. I bought a billet ring gear ($70) from ARC Racing they make for the GX200. I had to trim the thickness to fit in the offset between my ARC billet flywheel and the motor. Even after trimming, I still had to relieve about .020" off the casing to give adequate clearance. I clamped the ring to the flywheel and used a dial indicator to make sure they were concentric (to within .003", but ring gear was not perfectly round...). I then match drilled the ring to the flywheel, tapped the holes, c'sinked the mounting holes and used flat head screws with red Loctite. The starter is a GX200 Chinese knockoff bought on eBay for $23. No charge coils, but that's fine, I have a large marine battery in my boat.
In my conversations with ARC, they let me know they make an electric start flywheel for the HEMI. P/N 6686 and cost is $220. Not listed on their site, and is a special order.
Gonna try and keep it around 6k rpm cruising speed. My build is prob gonna be good for 8k. I wish there were an electronic governor for these motors. Something that monitors rpm and cuts spark above a certain pre-setable rpm. I've looked at rev limiters but they don't work for our magneto coil engines.
I have an outboard for when the water is deep enough, but when I know I'm going to be caught at low tide in the marsh I need the MM. Most of what I run is soupy black saltwater tidal marsh mud. Like thick ketchup. No weeds. I only need about 3" of water above the mud to keep moving, but if I stop and the hull is dragging, then I can't start again with the 6.5hp. Have to push pole or row. With the higher HP I'm hoping to be able to plow through the soupy stuff.
I have an outboard for when the water is deep enough, but when I know I'm going to be caught at low tide in the marsh I need the MM. Most of what I run is soupy black saltwater tidal marsh mud. Like thick ketchup. No weeds. I only need about 3" of water above the mud to keep moving, but if I stop and the hull is dragging, then I can't start again with the 6.5hp. Have to push pole or row. With the higher HP I'm hoping to be able to plow through the soupy stuff.
Yeah, sounds like you should be fine. An increase in power, the torque is sure to follow. This is why so many mud motors guy are opting for the 400cc or even v-twin motors because of the massive torque and displacement.
[video=youtube;LhAJw_EsUKs]https://www.youtube.com/watch?v=LhAJw_EsUKs[/video]
Man, an electronic limiter would be the bee's knees. That's why the Briggs LO206 caught my eye before I settled on the Champ.
[video=youtube;LhAJw_EsUKs]https://www.youtube.com/watch?v=LhAJw_EsUKs[/video]
Man, an electronic limiter would be the bee's knees. That's why the Briggs LO206 caught my eye before I settled on the Champ.
Almost ready to fire it up!
Got the flange on the header cut, shaped and welded. My TIG welder is a scratch start, no foot pedal so welds suck.
I made the header tubing from 3/4 EMT conduit. Took three attempts to get the bends correct. From what I read, long and skinny will help low end torque. I also wanted to try to get the open end far away from me when running.
I plan to run it straight open and if it is too loud, will make a 'glass pack' in the middle using that 2 1/2" tube you see on the floor behind the mud motor. (pics show my non-hemi stock motor that this build is replacing)
Flange has been 'ported' to match the exhaust port opening on the head.
The conduit is glavanised so I removed the zinc with acid. Takes about 30 minutes with 50% muriatic/water mix. Then rinse with baking soda solution to neutralize the acid. You shouldn't weld zinc as the released gases are poisonous.
Also found a GX200 elec start flywheel cover since the HEMI cover does not have the cover for the starter motor. Perfect fit, but red will be painted camo in the end...
I'll be trying to get it running this week if I can find the time...
Got the flange on the header cut, shaped and welded. My TIG welder is a scratch start, no foot pedal so welds suck.
I made the header tubing from 3/4 EMT conduit. Took three attempts to get the bends correct. From what I read, long and skinny will help low end torque. I also wanted to try to get the open end far away from me when running.
I plan to run it straight open and if it is too loud, will make a 'glass pack' in the middle using that 2 1/2" tube you see on the floor behind the mud motor. (pics show my non-hemi stock motor that this build is replacing)
Flange has been 'ported' to match the exhaust port opening on the head.
The conduit is glavanised so I removed the zinc with acid. Takes about 30 minutes with 50% muriatic/water mix. Then rinse with baking soda solution to neutralize the acid. You shouldn't weld zinc as the released gases are poisonous.
Also found a GX200 elec start flywheel cover since the HEMI cover does not have the cover for the starter motor. Perfect fit, but red will be painted camo in the end...
I'll be trying to get it running this week if I can find the time...