B&S 49-series (810cm3/49ci) for aircraft use - TiPi's Q&A thread

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Vigilant1

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It's a bit hard to tell from this image, but it looks like the 49- series Vanguard combustion chamber geometry might be a little different from the one on your head.

This is a screen capture from a teardown/marketing video on the Vanguard (video at:
). The engine has been run, so the dark deposits show the limits where the cylinder mates.
1589372820108.png

Here's a picture from your build log:
1589373072741.png

It would be a lot better to compare the actual heads in person, but it appears, to me, from these images some difference might be:
- On the Vanguard, it looks like the valve seats might project slightly into the combustion chamber. Is that perhaps a built-up area that both valve seats are on (dogbone shaped "platform" in the head? Or, maybe it's recessed and not raised at all). If the valve seats are actually projecting a bit from the roof of the chamber, then it would seem possible it has been done to allow the porting in the heads to be better (room for more gradual turn into the valves). Also, if the valve seats do project down, there would need to be other changes to keep the CR the same.
- The squish-area appears to be of a slightly different shape.

All for whatever it is worth. It's hard to make much of this based on the quality of the image of the Vanguard head, but to my eye there are some hints of a different layout that might bear further investigation.1589372820108.png1589373072741.png
 
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TiPi

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I think there are a couple of casting moulds. I found a picture from an engine that was built in 2014 (same as above) and it has the same heads as mine (built 2012). Later photos show a slightly different shape with a second step near the spark plug and both not reaching the machined head face. They could be a later version. The diameter of the combustion chamber still looks the same (gasket imprint is very faded).
NEW engine SE-33 XP 35hp
 

Vigilant1

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With the change of production location (and maybe tooling, parts sourcing) in 2018-2019, getting the current production bits in hand would be useful.
 

Vigilant1

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TiPi,
I re-read your write-ups of your engine runs. You mentioned that you advanced the ignition timing (from 21 BTDC to 29 BTDC), but I missed seeing how you did this. Did you move the magnetrons, re-clock the flywheel, or something else? (I'd guess the former). Also, based on what you've seen, do you have ideas on ways to achieve your goal of a sub-1000 RPM idle? I suppose the test club would have to have inertia similar to the prop you'll use to start working on that challenge.
Thanks again.
 

Vigilant1

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Wouldn't it make sense to just throw a simple EFI system on? Rather than continuing to fight with the carb?
;) "Wrestle with a carb" vs.
- buy and fit a new fuel pump
- buy and fit several sensors
- buy and fit injector(s)
- assure electrical power (it is now critical to flight)
- buy and fit the ECU
- explore and address the failure/limp home modes of every sensor/circuit/wire/connector. Enough power for flight in every limp home scenario?
Hmmm. :)
It is, but it's also been done before with acceptable results on the Briggs motors... My old lawn tractor for one.

Really you're adding a fuel pump and testing points of failure.
I've spent about 10 hours over the last 3 days trying to get the fuel system on a lawn tractor working. It is a very simple setup (gravity flow to a single-barrel Nikki carb feeding a single cylinder B&S 39 series Intek). It's still not running, nor do I know why it quit running.
Based on this very recent experience, I would like to apologize for retract my previous hasty dismissal of the EFI proposal put forward by Hephaestus.
 
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Hephaestus

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I feel your pain, there's a reason mine got converted :) there's a reason me and my group of friends have hoards of gm TBI systems squirreled away in our toolboxes. A little blinky check engine light doesn't say much but it sure says a lot more than a no-start :D
 

TiPi

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Ignition timing was advanced by removing the flywheel key and advancing the flywheel, then retorquing the flywheel nut. Not recommended for in-service but good enough for testing (the flywheel did move once).
To get a reasonable idle speed, the mixture on both throats needs to be adjustable. I have a larger carby on order that does have the idle mixture screws. The other challenge is to get even flow, it is a fixed shaft with 2 throttle plates and no air flow control. Not as important as mixture control, though.
Another option would be 2 decent single carburetors (Mikuni, Keihin, even Bing).
EFI is not off the table but last resort. Even with EFI, you would most likely need a 2-throat throttle body to get even cylinder charges (air) due to the uneven firing (and pulsing). Or trim the injectors slightly different for #1 and #2 for your normal operating range (75-100% power).
Single TBI would be nice but I'm not sure how the vibrations would be in an aircraft application.
 

Urquiola

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I was delighted thinking B&S meant the Barr&Stroud Sleeve-valve, Burt-McCollum type, not Knight, motorcycle engine, but it was not. One of it was offered in eBay in around $2600, or $3600, not long ago. Blessings +
 

Vigilant1

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From the latest post from your build log:
I have also found another assembly error! The flywheel end main bearing is slightly off-set from the oil supply hole. It is about 1/3 covered and at this stage, I'll leave it. If I can find a small enough Dremel burr, I might open it up a bit.

CIMG2324.JPG


That's the "flywheel end bearing" on a mower--it is potentially the hard-working and stressed "propeller bearing" to me!

This assembly issue, together with the absent valve stem seal you discovered earlier, are cause for concern. Until/unless we know that things have tightened up a lot now that B&S moved all production to the US, it seems prudent to pull a new engine apart and give it a good look before putting it in an airplane. And if doing that, it is natural to wonder if the engine can be bought as a basket of parts--a kit. Kinda like building a VW Type 1 for an airplane, expect virtually all the parts would have to come from the OEM.

A kit is unlikely. B&S sells parts through their distributors, and there's quite a markup. And it is very unlikely B&S would sell unassembled engines to be used in airplanes, they'd eventually become aware of the end use.
 
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Victor Bravo

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TiPi I want to sincerely thank you for your work on converting the Briggs engines for experimental aircraft use, and for making that work available to the public. Most of us don't have the level of expertise or understanding on this stuff that you (and a small handful of others) do, and sharing that knowledge with the rest of us is quite a gift. I for one am very thankful for that.
 

TiPi

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The best starting point would be a shortblock engine. Due to the work required for the conversion from vertical to horizontal, the engine needs to be opened up anyway, so taking the last few bits out is not much extra work. The heads need to be ported so again, complete strip-down.
I would strip any engine that is sourced from a "cheap" supply before putting it in a plane. Honda/Suzuki/Toyota engines out of near new cars maybe exempted, but industrial engines are mass-produced to a price and some variations in the assembly quality are to be expected. Just look at the different power ratings of the engines, and every single part is the same part number! It is a bit like solar panels, they use the same cell and get graded into the different output levels. The same panel varied by as much as 10-15%.
 

TiPi

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TiPi I want to sincerely thank you for your work on converting the Briggs engines for experimental aircraft use, and for making that work available to the public. Most of us don't have the level of expertise or understanding on this stuff that you (and a small handful of others) do, and sharing that knowledge with the rest of us is quite a gift. I for one am very thankful for that.
Thanks Victor Bravo, I would like to see a viable alternative for the smaller 2-stroke engines (Rotax 377/447 and Kawasaki 440) that are affordable and reliable. This is where the cheap flying is. The only way of getting an affordable engine is to use a mass-produced product that is nearly fit-for-purpose and just add/change the remaining few items.
 
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Vigilant1

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Tipi, thanks for your latest installment of your engine conversion thread.
- Flow improvements: As you pointed out, it looks like your efforts brought a significant improvement in the intake flow, but only a modest improvement in exhaust flow. I suppose the impact on overall engine performance would depend on whether the OEM engine's peak HP is limited by intake or by exhaust. Or, by something else.
I've got to find one of those heads and look at it up close. It would be interesting to do some HP/head-and-fin surface area comparisons with other air cooled engines. Any comparisons would be very rough (e.g. a sq. in. of aluminum at 400F right at the surface near the exhaust valve will transfer more heat than a sq in. of 200F aluminum at the perimeter of thin fins).
Those cast-in fin supports/blockages surely hurt airflow/heat exchange parallel to the fins, I'd think the holes you drilled should help somewhat. If getting rid of heat proves to be the next bottleneck to HP and reliability in the conversion process, I can see maybe removing the blockages entirely with an angle grinder and brazing on some new supports and fat fins, ala Bob Hoover's efforts with the VW Type 1.
Thanks again.
Mark
 
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TiPi

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Hi Mark,
The holes drilled are just to get some airflow at the root of the fin gap. There are probably 30 SE33s now flying without problems, but Igor did invest quite some time in getting the baffles right. As our climate is a tad warmer (5-10degC), I just thought it might help a bit.
I'm still trying to figure out what material to use for the baffles and which way to flow the air. I need to build a mockup firewall and approx cowling outline to visualise and place things.

The EX flow is difficult to assess as it is mainly turbulent. The actual exhaust gasses are hot and under much greater pressure than the flow bench. I think what counts more is the period of the overlap, where the exhaust helps scavenge the cylinder and the flow is better at very low valve lift.
 

Vigilant1

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It was encouraging to see the heads-down engine and the SD-1 firewall mock-up in your latest post. Looks like it will fit great, and give the higher prop hub and improved pilot sightlines you are after. Having the exhaust side of the heads up front should aid cooling considerably, and the carb at the bottom is (IMO) a big advantage. Just super. It's a pitty that B&S put the engine mount pads on the wrong side. :)
Exhaust headers from SS shower grab rails: A great idea strikes again. I know Pops used them for some of his VW exhaust runners.

I'll be interested to see how you join the AL intake flange to the SS intake runners. For a test rig (and knowing nothing), I'd be very tempted to weld a couple of L-tabs to the pipe, screw em into the AL flange, and just glob on a generous fillet of JB Weld to seal things up and call it a day, especially if the carb has its own support/mounting independent of the pipes.
For now, will you try to use the Nikki from the OEM 49-series engine, or will you try the larger one from the 54 series engine (that has adjustable mixture control)? You've invested a lot of effort in the present carb to make it as suitable as it can be, so giving it a try probably makes a lot of sense, but your data makes it appear that maybe it has reached its capacity. As you said--testing will show.
Thanks again.
 
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Victor Bravo

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Is it possible or advisable to remove all of the webbing or casting between the cylinder fins, then weld thin flat "straps" across the outer perimeter of the fins?

The idea is that the straps would prevent vibration cracking, but not create any resistance to airflow between the fins. The air would be flowing throujgh a mostly square channel, and you could grind out all of the "clog" or "blob" at the base of the fins.
 

Vigilant1

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Is it possible or advisable to remove all of the webbing or casting between the cylinder fins, then weld thin flat "straps" across the outer perimeter of the fins?
Grinding them out would be quick, which is nice.
Bob Hoover was a big fan of a new (at the time) welding rod that worked well for attaching "fat fins" to VW heads.
Welded-on straps would provide additional convective heat exchange area. OTOH, they would also intercept some radiative heat from the hot head itself (which otherwise would have left the head entirely and gone to the baffling).
 
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rmeyers

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Is it possible or advisable to remove all of the webbing or casting between the cylinder fins, then weld thin flat "straps" across the outer perimeter of the fins?

The idea is that the straps would prevent vibration cracking, but not create any resistance to airflow between the fins. The air would be flowing throujgh a mostly square channel, and you could grind out all of the "clog" or "blob" at the base of the fins.
Even better than welding is to do like the motorcycle manufacturers do and use a rubber strip. For example; a rubber strip of fairly stiff durometer, only slightly softer than the tread of most tires, .625 wide, .375 thick and as long as the finned height of the cylinder. Sliced cross-ways about a.250 deep and spaced at the actual cylinder fin spacing. Since you only sliced the rubber and didn't remove any material you can see that there will be considerable compression required to fit the rubber to the fins. The times that I have done this required a press and a little fixturing to get the rubber to insert all at once.

Depending on how thick your fins are you may want a little more than .375 thick and .250 deep slice.
 
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