# Briggs & Stratton Vanguard 23hp build

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#### bl_dg

##### Well-Known Member
Supporting Member
Hi friends,
I use a B&S 630 in my SD1 as direct drive and want to improve the power as my next project.
Current are the dates: max cruise speed is is about 100mph at 3600rpm
With the current prop, there is the max rpms at 4500 and this is my destination
with best regards
Juergen
Juergen,

Welcome to the forum and congratulations on your SD-1! How has the engine been running? How many hours on it?

What modifications are you planning? I like Tipi’s data-driven approach, so my initial focus will be on getting base-line info on the stock engine.

#### JuergenA

##### New Member
Hi ?bl_dg?,
the engine have about 220h current.First I want to increase the compression ratio, later new camshaft and roller vent arms to increase the vent opening...
with best regards
Juergen

#### mullacharjak

##### Well-Known Member
Roger mann of ragwings aircraft flew the Kohler 725cc 23 hp direct drive engine on the parasol and shoulder wing design.it flies very well as can be seen in video which is 27 years old.I read somewhere that a problem occured with the crankshaft.https://youtu.be/z38s0ZdqQ1ohttps://youtu.be/nh3RpyAaYwU

#### TiPi

##### Well-Known Member
Supporting Member
Hi ?bl_dg?,
the engine have about 220h current.First I want to increase the compression ratio, later new camshaft and roller vent arms to increase the vent opening...
with best regards
Juergen
Hallo Jürgen, increasing the valve lift on these engines doesn't give you much more power. The best bang-for-buck is doing a mild porting (remove/smooth the sharp corners, round the valve guide bosses) and a proper 3-angle valve job. Also look at the manifold to head and carburetor to manifold joints and align the port profiles (no steps/gaps). Another improvement depending on desired rpm is a larger carburetor (28mm instead of the 25mm).
For rpms over 4,000, strongly recommend the billet conrods. Also check out Kevin Armstrongs info on Youtube, he modded a 38 with a re-drive and flew it for a couple of hundred hours in a trike.

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#### bl_dg

##### Well-Known Member
Supporting Member
Hallo Jürgen, increasing the valve lift on these engines doesn't give you much more power. The best bang-for-buck is doing a mild porting (remove/smooth the sharp corners, round the valve guide bosses) and a proper 3-angle valve job. Also look at the manifold to head and carburetor to manifold joints and align the port profiles (no steps/gaps). Another improvement depending on desired rpm is a larger carburetor (28mm instead of the 25mm).
For rpms over 4,000, strongly recommend the billet conrods. Also check out Kevin Armstrongs info on Youtube, he modded a 38 with a re-drive and flew it for a couple of hundred hours in a trike.
Juergen - Whenever you are ready to work on your engine, it would be useful to measure the center-to-center length on your rods, to see if you are experiencing any stretch at those higher rpms.

Thomas - thanks for the tip on the carb size. I also found Kevin's youtube channel.

#### TiPi

##### Well-Known Member
Supporting Member
Juergen - Whenever you are ready to work on your engine, it would be useful to measure the center-to-center length on your rods, to see if you are experiencing any stretch at those higher rpms.

Thomas - thanks for the tip on the carb size. I also found Kevin's youtube channel.
The problem is not stretch of the rods, it is fatigue failure of the cast aluminium. Cast alu is quite brittle and any small imperfection in the surface (or internal) will start a minute fracture that will slowly progress until the remaning cross section can't hold the load. Increasing the rpm increases the stress (load) by the cube square eg twice the rpm = 4x the load. Plenty of examples in mowers & mower racing with increased rpm.

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#### bl_dg

##### Well-Known Member
Supporting Member
The problem is not stretch of the rods, it is fatigue failure of the cast aluminium. Cast alu is quite brittle and any small imperfection in the surface (or internal) will start a minute fracture that will slowly progress until the remaning cross section can't hold the load. Increasing the rpm increases the stress (load) by the cube eg twice the rpm = 4x the load. Plenty of examples in mowers & mower racing with increased rpm.
So maybe do penetrant dye testing on the rods and crankshaft. It won't catch everything (especially those internal flaws) but if one is taking things apart anyway, it might be worth the effort.

#### TiPi

##### Well-Known Member
Supporting Member
So maybe do penetrant dye testing on the rods and crankshaft. It won't catch everything (especially those internal flaws) but if one is taking things apart anyway, it might be worth the effort.
Yes, that is a way to check for surface defects. The other methods to reduce the likelihood of a crack developing is to smooth the surface (remove the cast mold lines) and polish the surfaces. Also remember that with the B&S engines, the bearing surface is also the casting, no bearing insert. So anytime you have a bearing defect or wear, you need to replace the rod(s).

#### TFF

##### Well-Known Member
When racing 5 hp Briggs stock but blueprinted in Karts, the best engines made around 10 hp at 6000 RPM. Fuel was methanol. Rods lasted three races including practice. Fourth, and it came out the bottom. Like clockwork.

Step out of the stock class allowed aftermarket rods. A friend had years on the modified engine rods. They also have bearing inserts.

RPM was a contributing factor. 6000 is a lot. They also were governor free, so you really got full throttle, not 3/4 throttle until it gets loaded up. Full manifold pressure, not partial part time.

If it was an option, I would want better rods than stock ones.

#### Ken Powell

##### Well-Known Member
Are billet rods with inserts a significant upgrade? Is a billet rod close to a forged rod for strength?

#### bl_dg

##### Well-Known Member
Supporting Member
Are billet rods with inserts a significant upgrade? Is a billet rod close to a forged rod for strength?
ARC makes billet rods, and they’re currently about $125 each. ( Anyone know of other makers? ) In general, a forged rod may be stronger than a billet rod, but I don’t know by how much. Either one is way better than a cast part. TFF (and Tipi) brings out a good point - some of the after-market rods include a main rod bearing. The Vanguard parts catalog does not show a rod bearing on the stock rod. Then again, these engines run all day at 3,600 rpm and seem to last quite well. #### TiPi ##### Well-Known Member Supporting Member ARC makes billet rods, and they’re currently about$125 each. ( Anyone know of other makers? )

In general, a forged rod may be stronger than a billet rod, but I don’t know by how much. Either one is way better than a cast part.

TFF (and Tipi) brings out a good point - some of the after-market rods include a main rod bearing. The Vanguard parts catalog does not show a rod bearing on the stock rod. Then again, these engines run all day at 3,600 rpm and seem to last quite well.
None of the current B&S or Vanguard engines have a separate bearing insert. The cast alu rod is a compromise between strength and suitable material for the bearing, so not ideal. The forged rod is still a compromise but to be able to forge the material, it needs to be a bit more dutile, with the forging process itself making it stronger as well. With a billet rod and bearing inserts, the material choice is simply for strength and durability. The bearing shell (surface) is then designed for low friction and durability (usually soft metals). ARC is using aircraft grade 7075 T-651 aluminum for their billet rods.

#### bl_dg

##### Well-Known Member
Supporting Member
Eiffel clubs: I’m still waiting for H-D to deliver my new jointer. The horses on the wagon train must be tired because it took 8 days to make it the 200 miles from the DC to the local store.

Engine: In the mean time, I picked up some stainless steel plate from a local salvage supply store to make some exhaust flanges. For the exhaust pipes, I got a 1-1/4” stainless steel grab rail at Lowes. (This will just be for testing, not for flight.)

I‘m going to the Dawn Patrol Rendezvous at WPAFB this weekend because, you know…. airplanes!

#### bl_dg

##### Well-Known Member
Supporting Member
Finally got my planer and jointer for making the Eiffel clubs. In the mean time, I stripped down the rear (or bottom) cover from the vertical shaft engine. Not much to it. The oil pump feeds the plain bearing on the PTO end and that's all. The suction side of the oil pump has a simple plastic screen to keep out any large scraps. To convert for horizontal use, I'll need to remove the ball bearing that is plugging the 'bottom' of the drill-through hole and then plug the 'top' where the suction screen is currently located.

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#### Hawk81A

##### Well-Known Member
You're using the base from a vertical instead of the stock rear cover? What's the reason? Longer bearing (vs Ball bearing)? Extra oil capacity? Dennis

#### bl_dg

##### Well-Known Member
Supporting Member
You're using the base from a vertical instead of the stock rear cover? What's the reason? Longer bearing (vs Ball bearing)? Extra oil capacity? Dennis
I’m attaching the prop on the flywheel end, so I don’t need anything on the PTO end. The idea is to use the stock flanges on the vertical pan for mounting the engine. I won’t know if it will work until after I run my base line on the engine and begin the tear down. The goal is to eliminate the weight and complexity of a bed-mount engine support and attach the engine directly to the firewall. (with small spacers or vibration isolators for air gap)

#### bl_dg

##### Well-Known Member
Supporting Member
With direct drive, you would have four cases:
1. Tractor/flywheel end - you're pulling the crankshaft against the engine case.
2. Tractor/PTO end - you're pulling the crank/cam gear against the rear cover. (mass on each end of crankshaft)
3. Pusher/flywheel end - you're pushing the crank/cam gear against the rear cover. (crank in compression)
4. Pusher/PTO end - you're pushing the crankshaft against the engine case. (crank in compression) + (mass on each end)

I'll know more once I have the engine apart, but I would like to add a thrust bearing if there is adequate material for machining. (and oil supply)

#### Vigilant1

##### Well-Known Member
Supporting Member
Thrust bearing:
1l Is it needed? Finding info on the SD-1s and Lucioles now using them could probably tell a lot. By all accounts, Colomban et al spent a lot of time working through all aspects of their B&S 627 conversion.
2) If there's a need, room, and enough oil splash, a shim or two with oil grooves might be all the "bearing" that's needed.
There are strong indications that the vertical engine case half won't work with the stock horiz case half, crank, and cam. It would be an amazing coincidence if by chance shims on one or both ends in combination with other parts solved two problems (thrust bearing and rotating part alignment).
My suspicion is that the use of the vertical shaft case half will likely be a dead end, but maybe not.

#### Hawk81A

##### Well-Known Member
I have built multiples of both vertical, and horizontal Vanguard engines. Most were the 18HP. IIRC, the gasket for both was the same, so the cases MIGHT be interchangeable. From my experience (mowers and industrial applications), the horizontal shafts had a ball bearing on the PTO end and aluminum on the flywheel, while the verticals had aluminum on each end. The verticals did have a longer bearing surface.
One thing I can tell you: the Vanguard engines DO NOT LIKE TO IDLE SLOW. I rebuilt / salvaged ta least three (all horizontal applications) that suddenly had connecting rod failures due to oil starvation - yet were full of oil. I only recently found out about the minimum idle of 1100 RPMs (there is a special governor spring to maintain this minimum speed - many idle at around 1700) The lower idle speed aparently doesn't provide adequate oil pressure for the connecting rods.
While there may not be enough "meat" on the flywheel end, I would think machining a little off the PTO end bushing (vertical application) and installing a roller thrust bearing with two washers. The ball bearing is not a press fit on the crankshaft. Dennis