Briggs & Stratton 993cc "Big Block" engine conversation thread

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Lucky Dog

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I received my Briggs Big Block (993cc) last Friday. Here is the engine I ordered: 61E377-0027
This engine has a tapered Crank and is 37HP EFI. Delivered weight was 124.65 lbs. I then stripped it down to the long block (removed the EFI, flywheel and everything else except the oil cooler). Hold onto your seats - the long block weighed 68.05 lbs. I'll weight individual components later this week.
I also did some parts comparisons with the 61G 40HP Marine engine. The head, intake valve, retainers, keepers, valve springs (pink) and push rods are all the same part numbers. The rods and the rod bolts are the same. The exhaust valve is different. The camshaft and pistons are different. The EFI appears to be the same except for different mapping of the ECU.
Could you weigh the flywheel for us? The early ones were 21 pounds, but the later ones use a different casting. THX!
 

TiPi

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Hi Ken,

Good info. Looks like the 61 long block is not that much heavier than the 49 long block. I'll get my bits together and weigh the same configuration to compare (long block only +cooler).
If you open up the engine, could you please take a couple of photos of the crank shaft? I'm interested to see if the crank is cast (cast steel) or forged. The centrelines on the flanges tell the story.
 

Ken Powell

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My engine has a governor so it has to be opened for removal. I'll take pictures at that time.
Question: Do I need to replace the exhaust valve (of unknown construction) with a SS exhaust valve or the 61G Marine engine exhaust valve? I'm leaning toward the SS exhaust valve. The rest of the valvetrain components are the same as the Marine engine except for the cam.
 

TiPi

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EX valve: a bit hard to tell without some pics. I found a big difference in the 49 between the "Professional/Commercial" and the Vanguard valves The Vanguard is a bit heavier (41.1 vs 40g) & sturdier and has a much better finish (machined head). The other valve has a thinner and stamped head.
 

Vigilant1

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Good info. Looks like the 61 long block is not that much heavier than the 49 long block.
Out of the box, the carbureted versions of the 810cc and the 997cc engines weigh 92 lbs and 125 lbs respectively. If I recall correctly, the 49-series based Spacek SE33 weighs 77lbs ready to fly (including prop hub). The weight reduction effort wasn't extreme (e.g. use of slightly lightened OEM flywheel to allow the OEM starter, alternator ignition to be retained, etc).
If the same approach and 16% weight reduction is applied to the 61 series engine, it will weigh about 105lbs.
This comparison doesn't apply well to Ken's project, as he's planning to mount the prop to the PTO end, not mount a prop extension onto a modified, lightened OEM flywheel.
 
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blane.c

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The prop obviously can substitute for the flywheel, but what are you going to do with the original flywheel regards electronics and starter drive? Move everything over to the backside of the prop (lightened of course)? better mojo? Or leave it on the original side and have essentially flywheels on both ends of crank (even if one is lightened)? Flywheels on both ends is bad mojo?

I mean what is the best solution?
 

Lucky Dog

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My engine has a governor so it has to be opened for removal. I'll take pictures at that time.
Question: Do I need to replace the exhaust valve (of unknown construction) with a SS exhaust valve or the 61G Marine engine exhaust valve? I'm leaning toward the SS exhaust valve. The rest of the valvetrain components are the same as the Marine engine except for the cam.
Briggs stock valves are two piece (the shaft is welded to the valve). It is rare, but when used with high lift cams and dual valve springs at high rpm, two piece exhaust valves can separate and do bad things to the engine. We don't run them above 5000 rpm and use mild springs, so it's not a worry. That said, switching to stainless steel one piece valves will set aside that worry, and they are ground with a flatter curve at the root and a three-angle grind at the seat. Both treatments enhance flow and can deliver measurable horsepower gains. So, if you have the cash, you may consider the upgrade. If it were me, however, I'd spend my money on flat-top high compression pistons to boost torque.
 
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karmarepair

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The prop obviously can substitute for the flywheel, but what are you going to do with the original flywheel regards electronics and starter drive?
My plan (unrealized) is to drive an alternator using the prop hub, use a crank trigger ignition, and for the time being, punt on the electric starter. I'm trying to minimize parts I have to custom build. I have the prop hub (from Competition Propellers) and a belt drive PM alternator off a Kubota, and Midwest Super Cub has the crank trigger ignition.
 

WonderousMountain

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Question: Do I need to replace the exhaust valve (of unknown construction) with a SS exhaust valve or the 61G Marine engine exhaust valve?
Were it me I would go ahead & grab the Marine tappet.
SS is only really needed for Methanol race fuels, but it
is better than stock, has a solid track record. Stellite if
used with hard valve seat will have longevity. Not sure.
~C.K. LouPai
 

Ken Powell

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The prop obviously can substitute for the flywheel, but what are you going to do with the original flywheel regards electronics and starter drive? Move everything over to the backside of the prop (lightened of course)? better mojo? Or leave it on the original side and have essentially flywheels on both ends of crank (even if one is lightened)? Flywheels on both ends is bad mojo?

I mean what is the best solution?
I am removing the flywheel and will hand-prop the engine. Prop will be direct drive on the PTO end of the crank. Intake will be twin carb. Separate exhaust. Ignition will be separate for each cylinder with HEI for each. Each HEI will have 2 pickup coils - one at 10 degrees BTDC and one at 28 degrees BTDC with starting on the 10 degree BTDC pickup and running on the 28 degree pickup. Ignition will be probably be battery only (total loss) but I may design a charging system depending on total weight. I really do not want to go over 100 lbs for the entire FWF. I am basically treating all systems as 2 separate single cylinder engines.
 

rv7charlie

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Alternators /brackets/belts/bolts/pulleys etc. belong in a museum since we have solar panels and lithium-iron batteries.
OK, you've been making similarly bombastic posts for a while. Time to show your work. For this particular contention (replacing an alternator with solar panels), show us how you can generate enough current with solar panels on an a/c to replace the current from an alternator. To make it simpler for you, I'll let you ignore the condition of flight at night.
 

Stuffengineer

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About 12 pounds for solar panels and charge controller. Think I would rather have an 20 amp alternator. Is there any chance that a permanent magnet motor could be selectively powered by the battery and used as a starter/ alternator. Similar to the set up on a golf cart.
My understanding is that a flywheel one end and a prop the other is not a good idea, but could you have some weight say 5lbs and replace flywheel with flexplate and ring gear/ ignition trigger wheel?
 

Ken Powell

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I have seen some guys talking about a starter/alternator per golfcart. Someone weighed on and it weighed close to 20 lbs so some other source would be needed.
 

rv7charlie

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The 'traditional' golfcart starter-generators are brushed, DC systems. I think there may be a few production cars using multi-phase 'AC' systems (brushless DC motors) [edit]: as starter/generators, in cars designed to shut off the engine at stoplights. The controller drives the sequential coils in start mode, and rectifies/regulates the output in alternator mode. Trick seems to be getting enough rpm via a reduction system in motor mode to get enough torque to spin the engine. (Ken, Talk to Monty. ;-) )
 
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blane.c

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I am removing the flywheel and will hand-prop the engine. Prop will be direct drive on the PTO end of the crank. Intake will be twin carb. Separate exhaust. Ignition will be separate for each cylinder with HEI for each. Each HEI will have 2 pickup coils - one at 10 degrees BTDC and one at 28 degrees BTDC with starting on the 10 degree BTDC pickup and running on the 28 degree pickup. Ignition will be probably be battery only (total loss) but I may design a charging system depending on total weight. I really do not want to go over 100 lbs for the entire FWF. I am basically treating all systems as 2 separate single cylinder engines.

I really like this approach.
 

Lucky Dog

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Small, permanent magnet alternators used on popular lawn tractors are available with 16 and 20 amp outputs. They cost about 65 USD and weigh 3.0 to 3.4 pounds (from memory). Many are flying in experimental aircraft today. Ditching the 19 pound flywheel and stator for this remote alternator (assuming a pound for mounting hardware and an aluminum drive pulley) can save up to 14.4 pounds. It's a sound idea @Ken Powell. Finding a lightweight alternative to their monstrously heavy flywheels is the key to successfully repurposing industrial V twins for aviation.1643475287300.png
 
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