Episode 54 What I think about this Yamaha APEX engine? 

I think your theory of the head gasket is correct Brian. Thanks for your honest and very detailed way of sharing your progress. Keep it going, we will be here.

Combustion pressure leaking into the cooling system causes all kinds of problems. Glad you didn't severely overheat that first engine while testing. It will be interesting to see what the mechanic finds inside. See if he will take some photos of the damage as he tears it down. We'd love to see.

Very rare these days to finds someone who is as honest and open as you are Bryan, keep up the great work

Great breakdown of engine choices!Thanks for keeping the information objective. Sorry to see your engine having problems, but you’ve saved the next guy many many headaches. Loved every minute of this video. Thanks Bryan!

Just came across my feed with this video. Vary impressed. Went through some of the same issues many years ago with a Subaru engine on a Kolb Mark IV. After a little work and time , it ended up being a fantastic flyer, for many years. Good luck to you, I really enjoyed watching your video and I will go back and catch the others.

Just watching this again and enjoying it as much as the last time. Solid gold Bryan!

Thank you for being transparent with your issues. I think you are correct in your assessment of your engine problem that it was an unknown issue from the beginning. I think you are sincerely giving the Yamaha engine an honest review. I am a fan on this engine. Keep going with the videos we are all enjoying your journey. I hope to be there one day with my own plane with a Yamaha.

Absolutely awesome awesome awesome episode. I like how you dissect every aspect of your decisions and thoroughly explain why.

as a non flyer I totally enjoyed your description in an easy to understand way. Loved it. Look forward to the follow up on the engine "autopsy"

Thanks for sharing, and especially the head gasket issues on a used sled engine. It goes with what I posted on the FB yamaha page. Best of luck with the new engine. Love your videos. Very detailed. You are very thorough!

Thanks for sharing. Love the video. The head gasket makes so much sense. I think it is smart to have two engines. You are crossing new grounds with that engine and learning so much. Love it.

Very useful film, and glad you were able to bounce back so quickly! Re: two channels or not, my understanding is the more people not clicking on a thumbnail the less the algorithm likes you, therefore anyone not interested in bikes is going to have negative impact on your flying channel, which would be a shame.

Excellent discussion. Thanks for sharing your experience and thoughts.

Nice video. I hope we get to see some photos and measurements of anything out of specs from the repair shop.

Good update. I have used a product called Mend Tite by Zecol and Bars Leak with some success on older vehicles. I haven't seen any detrimental effects from either other than sometimes they don't stop the leak. I have it in an old truck that had a slight head gasket leak that it worked pretty well on, but I had to add more stop leak from time to time. All stop leaks are temporary at best in my opinion. Ultimately if you have a leak it's best to fix it correctly. I don't think I would put any of them in an airplane.

I think the Yamaha is a great solution. Being an early adopter is always going to be extra work. Thank you for sharing, your experiences will help the next guy. I’m planning a super light Yamaha Phazer build in the near future, also great power to weight.

I really appreciate the effort you put into being thorough in both your analysis and explanation of the airplane and the issue with the engine. I agree with your take on what happened with engine #1 It might be worth the $ and effort to send a few oil samples from this engine and the freshened one to Blackstone Labs for a workup on the oil. I've done it with several engines over the years and was always happy with the peace of mind the numbers give me, and, once a pattern is established if a change happens the odds are you'll see it in the oil before it goes south on ya. Just a thought...

Sorry you’ve had this problem with your engine. I really appreciate your analytical approach to discovering the issue and being able to fix it. I sure hope the new engine will give you the results you are looking for.

Great video! Thanks for sharing.

Great video Brian will consider the Yamaha in my Dakota Hawk.

One of your best videos ever

👍🔥Awesome review, appreciate your unbiased honesty and objective approach to the compromises, thank you. Recently took notice of UL Power Aero engines. My initial impression so far is it’s a top contender with little compromises, especially in the direct drive segment. Very interested in a head head to head comparison with the Yamaha in this exact mission and aircraft type. 😉🔥❤️😎

Sorry for the troubles but thank you for thiscsuperb, detailed, well thought out and articulate video.

Interesting to say the least. I'm really wanting to know what the TBO numbers will look like. And the bright side is, you can get the rebuild done at your local sled & bike shop.

Thanks Brian, be sure to share what you think of your engine rebuilder. What is your thoughts on ECM or battery redundancy? Definitely will go with Brian D's ACM ECM/harness setup. Thanks as always for sharing your experiences.

Thanks for that video. It's good info for any experimental aircraft

Hi Brian as usual great videos so much useful information thank you very much

This was a great episode, and I as well appreciate all of your honesty. I think the Yam is a contender..

Great info, appreciate the honesty and time.

Thank you for the update!

Pretty cool stuff actually; Like the way you just calmly work through it

Great episode and outcome. I learned about coolant additives as a poor college student. No way would I try it again. Also, I've had a car with a tiny head gasket leak which was not visible on the outside of the engine, but it was pumping combustion gases into the cooling system - which caused the cap to vent. It was a broken head bolt in my situation but that is unlikely with the Yamaha. Thanks for sharing your experiences.

I put 1300 trouble free hours on a EA-81 Soob conversion in my first RANS S-7, and loved rubbing that number (as it grew to the total) in the noses of people who would at first diss such a relatively unusual engine choice! More recently, after reaching TBO and beyond on my current 912S, with zero issues, when talking to a die hard legacy engine pilot the numbers kind of put an end to any dissing of the Rotax. Point being, build those hours big time, nothing succeeds like success, 10 hours is a blip, 500+ hours and up will really prove the concept. Looking good!

Very nice piece, It shows that you are a talented "Engineer" "root cause comes to mind

Very nice video appreciate all the info and thanks for sharing.

I appreciate such an objective and in depth review of this particular option. The power/weight/cost certainly seems like a no brainer! What is the TBO that guys recommend with these engines? What is it like cruising at 7900-8800 rpm compared to 200-2200? Keep the videos coming whether it's fly or bike adventures, it's all great content!

Thanks for all the engine info !

This was an epic episode! Feel like viewers should receive technical education credit fot watching.

Fantastic video Brian, very entertaining and educational. There are another couple of Apex options you did not discuss, although I’m certain you must have at least a ‘view’ on. An ‘Edge’ modified Yamaha and a ‘turbo’ Apex. Would appreciate any thoughts you have on these, yes I appreciate that either/both are expensive. Cheers.

Based on my experiences with rebuilding motorcycle engines I suspect that anyone with the mechanical aptitude to build an ENTIRE AIRPLANE can easily overhaul their own Yamaha engine. Granted you would need to pay a machine shop for any needed reconditioning (bore/hone cylinders....resurface head) but the assembly part isn't rocket surgery. I'm also amazed that even one single person is willing to install an engine that was run in a snowmobile without rebuilding it and then bet their life that it will probably run alright.

Great videos, so informative…. and (for what it’s worth) I think you made the right choice on engine. Good decision to get a second Yammy motor for a spare: there’s little worse than a sunny day at the airport with your aircraft grounded / in bits! Several people have commented on getting the oil analysed regularly: I spent 20+ year racing old cars, mostly early 911s, and we found that you often got early warning of problems from the oil check. In fact we ended up using the oil check & compression check to decide when to do a rebuild - if the race engine passed both tests, keep going & save the money for later! It might be interesting to try a flight-adjustable prop on that motor: if it has a sweet-spot around 8k you might be able to optimise cruise performance with higher throttle setting & ‘pulling it down’ to 8k with the prop setting (of course I might be missing something…). I believe that someone will soon try to put an adjustable prop with ‘beta’ reverse thrust setting as a way of shortening the STOL Comp landing phase ( rather like Mike Patey’s Draco ) Anyhow, many thanks for your videos: great to see someone ready to share so much detail. Fly safe! Peter / England

Love the overhead view from the cockpit.

Loving your content. Big fan of Trent as well but your stuff makes me want to grab a kitfox and do an apex build. Thank you.

I've had coolant additive completely ruin a heater core. It flowed coolant, but inlet and outlet temps were almost identical after the client added the additive. There was little or no heat transfer any longer. Not sure how much damage it did inside the radiator. Any film on the interior surfaces of the passages in a heat exchanger, severely lessens the heat conductivity of that component. We found the leak, repaired it properly, flushed the system with a chemical that would dissolve the additive, then with distilled water before filling with coolant and returning the machine to service.

Great explanation thank you.

Thanks, Bryan. I really appreciate the time you put into this video series, and I'm sure I'll be referring back to your videos as I work through the rest of my build (a Series 5). I too considered a lot of alternative engines, but in the end I wanted a reliable, proven package so I could just fly and not be faced with problems I don't know how to solve. I spoke to John at Kitfox and learned that their firewall forward kit for the Rotax 912iS is extremely complete, since that's the engine they use on their S-LSA product. So, I've got that engine on order and my prop is arriving any day now. Maybe by the time I wear out the Rotax, the Apex will be a mature option and I can make the upgrade!

Awesome video, I’m a new subscriber, Thanks for the detailed information. I am interested in your opinion about why naturally aspirated and not turbo?

Great channel and conent! Viking has the 1.5L Honda 130 Hp (no turbo) and they also have a 1.8L Honda 150 Hp (no turbo)... some Rans S-21s are now running the 1.8L 150 Hp engine. The Viking 1.5L Turbo at 195 Hp is probably not a good choice for the Kitfox but matches up exceptionally well for the CH750 SD or a Rans S-21 Outbound.

Best airplane/engine option video ever! Thank you! Mike Fitzgerald Calgary Canada 🇨🇦

Very good presentation 👍

Dam that’s a beautiful plane. I live in Boise can’t wait to build mine

It sounds to me like you most likely had a slight head gasket leak in the first place that over pressured the cooling system and caused the weeping leak at the radiator weak spot.When you added the stop leak, it did plug the weeping leak but wouldn't stop the head gasket leak which injects compressed air into the cooling system. Unlike the radiator leak which released excess pressure out of the cooling system. That's how stop leak products are designed to work from the inside out not outside in, as was head gasket leak. In the end the water system failed because of over pressure. I write this as you have discovered. Any how I see that problem all the time with high performance diesel engines in my fleet. Beautiful plane b y the way! Thoroughly enjoyed watching your vids of your building of it. Keep it going!

your instincts are right with the additives. I have only used it on vehicles that were not worth repairing or customers did not have the funds and wanted to roll the dice. If leaks were tiny like 12-8 oz over the course of a 4 or 5 hours it seems to work and only for head gaskets or cracked heads. Another thing i learned over the years is if you have a bad head gasket/cracked head . The time it takes for the engine to heat up and for the silicate to glass up in the additive it usually makes it way to the oil and your oil analysis will show extra silicate which is not advantageous for engine wear. which Im sure you know.

Looks like you recently posted a follow-up video so need to watch that now.

Awesome video, ty so much!

I am looking at engine choices for my S-21 since the Titan 340 is basically Chinese unobtainium now. I am leaning 915, but the cost is nosebleed territory for sure, but then so is the Titan now … if you can get one. One thing about the Yamaha is that you mention it is designed for 200 HP and you are derating it to 160. Well, very few auto or Motorsport engines are designed to run at a significant percentage of their max HP for extended periods. They will make high HP for short times, but many won’t last long when running at high outputs for long periods of time as in aircraft or marine use. So, while the motorcycle and sled engines may be rated for 200 peak HP, but will seldom make more than 50% of that for more than a few seconds or minutes at time. Most of their life will be spent making 20-40% of their peak output. So, if you run at even 100 HP for long periods, you are running the engine far harder than it is typically run in a bike or sled. It will be interesting to see how the engine does after 2,000 hours in an airplane. Do you know of any that have run even close to that long?

Great!! I was loving the 915 just based on reputation but the cost is ridiculous. This Yamaha conversion might be the best option. Thank you

Great video! You are likely correct that the leaking head gasket issue was there from the beginning. Most likely cause is lack of proper/timely coolant changes by the previous owner. As a professional mechanic, I can definitely say, that a large part of the motoring public are totally lame when it comes to maintenance. Oil changes are about all a lot of them do. Any time work is done that opens the cooling system, after the first engine run up to operating temperature, let the engine cool down completely. Then open the system and add coolant as needed. Often, you have an air pocket in the system. This air pocket will work itself out after a good run. Failure to do this, may lead you to later think that you have a leak.

Thank you for being honest you don't have to share this info and you do I've had Yamaha street bikes with similar engines and never had a problem they've always been great I used head gasket sealer in the coolant 1time to get me home and I regretted it bad what a mess it seems the Yamaha is the best choice after listening to you break it down I heard Yamaha is now going to start making aircraft engines for lightsport probably going to be expensive lol great vlog as always thanks brother

We have data logging on our liquid cooled drag cars and I run a water pressure channel in the system. It clearly shows pressure events (if/when they occur)... spike from cylinder pressure is super clear (I was fighting a problem when I decided this would be a good channel to add). I would be tempted to do the same on a liquid cooled kitfox .... which I hope to build one day.

Agree. On our car, I had bad experience with those bottled head gasket repair. Damaged the water pump seals. Only sealed the combustion leak for a month. It's negative utility, it is not a fix.

Great video I really like your honest opinion yeah that is some ridiculous prices

Thanks for telling the whole story as usual! Where is the design engineer when you need one? Also, I wonder if the head can be modified for better cooling since it was designed for cold climates.

hi ive thoroughly enjoyed your content from start to finish. I am at the very beginning and plan on doing the same as you. could you please answer the following question. what is the overall length and height of the plane? i am trying to determine if my garage will work as the spot as to where to build it. thanks

Rotax four cycle engines where and are WAY expensive compared to any experimental versions in the market. the reduction gear mechanism is a piece of concern. No Rotax for me. I am really happy about what aí hear from Yamaha users. Thanks for your feedback.

Would you be able to bypass the air to oil cooler to see if the water to oil cooler is adequate now? Keep up the great testing and diagnostics, youre helping a lot of people!!!

Great info

The newer coolants can have problems even with other coolants, gelling, etc.. Worth looking into.

I have a hunch that original engine possibly got pretty hot at some point when it was still in the sled chassis.

Did you consider the Yamaha 988T at all when you were deciding on engines? I saw the @Project 2 Aero guy who's putting one in his rans 21. Very cool looking project. Skytrax built him a gearbox for it. Would love to do something like this just not sure if I'll want to do it on my first build.

I’m really drooling over the potential of the Higgs Diesel engine line. Their Falcon engine would be a totally awesome option for the Kitfox, and a great option for bigger aircraft in the nominal 180 to 200 hp range (the Cozy MkIV, for example). Nothing but promises and pamphlets right now; hopefully they don’t go the way of the Gemini.

in 2003 I was riding an R1 at around 130mph on the freeway on a long straight 5 hr 550km journey late afternoon around 22oC. It had 8,000kms on the clock. Bought it new. My baby. I was lying down as one does chin on tank. I smelt coolant and a split second later as i was thinking is that coolant smell I saw green spots of it hit the screen. I hit the engine kill switch immediately, pulled the clutch and coasted to a stop. Called for a tow. The temp gauge was definitely on the normal mark. Yamaha dealer found the tiny stone hole with stone embedded in radiator and repaired the radiator. They started the bike and test drove it and same symptom as yours. Was blowing coolant out. No water oil mix etc. They had to do head gasket. They explained that in that split second in a 1-2mm section in that part of the gasket the lack of coolant had caused the heat to melt and damaged the gasket. They checked the head. No need for a skim. Known issue... I'm non mechanical and didn't see gasket. Dealer mechanic is trusted old mate and used him for years. At cooler "speed" running temp you loose coolant it'll do head gasket in 3 secs or less it seems.... Hope that helps in the future bro. Love yr videos

Did your rebuild on the first engine go good? I have an Apex I just bought and I am thinking about getting it rebuilt before I install it. Thanks

Great great video and yes chemicals never fix a problem.

Thank you for the update. Where are you sourcing the engines?

I've been riding motorcycle for 40 yrs and I'm quite accustomed to hi-revving engines. However, I don't know if I could ever get used to seeing a constant 8000+ RPM as my "cruise" setting. I have no doubt the Yam engine can handle it but it would just feel "busy" to me!!!

I think you should try and Make it go fast. Be interesting to see the envelop and what it takes to go to both extremes.

Looking forward to a longevity report. Sending oil out for contamination tests?

a quick fix coolant is a really bad idea, a CO2 test in the coolant tank is an assurance test, but ya they get beat up by the snowmobile guy that's why I wanted to go true mine before installation. that would be the right time to get the crack welded and balance and to put the 10/1 ratio GP piston for eventual turbo boost.

Awesome!

Great video, What is your opinion on the desser tires compared to the Alaska bush tires in performance only. Not weight or ware. Also how much psi are in the desser tires. Thanks

Just wondering, what’s the weight of your Kitfox 7 with the Yamaha engine? It’s the “STI” package correct? Thanks

Love all the commentary and info on Yamaha Apex. Need to do more homework.

Leak checking - one can get (or fabricate - that's what I ended up doing for my Rotax) an adapter to replace the radiator cap and pressure test the cooling system without draining / removing anything. In my case, I ended up finding that the water pump was weeping, but I ended up leaving it pressurized overnight before I found it since the leak was very slow with the engine not turning. Leak stop stuff - no thank you...

I wonder if a turbo would reduce RPM for Cruise an adjustable prop would be handy typically boost will bring power curve to lower RPM.

Old japanese bike guy here. Having used Yamaha, Honda, Kawasaki, Suzuki, here is my thought. If you ever use a Suzuki, especially tear one down and look at it from a durability standpoint.....ohh, I see now. That Slime tubeless tire sealer, disguised as coolant stop-leak is clever...and useless. Horse manure was in the old pellet style Bar's stop leak. It's a no-no in anything you care about. Sir, your learning curve is quick. Let me know if you fit a Suzuki in there. Not only will you win, you'll do it again next year on the same engine.

Was it not feasible to move the lighter engine forward for balance considerations? I'm not getting this for some reason.

I’m 12 mins in. Who needs an interviewer when you are answering all the good questions. Thanks mate. 22 mins in, do these engines get stripped and rebuilt before putting it in?

I suspect swapping engines was probably more work than pulling the head off would have been. If the head was warped there was likely a local machine shop that could have decked it too. Even if you were interested in a major rebuild, I can tell by your videos (as if just being able to build a kitplane with significant mods wasn't enough) that you could likely teardown and reassemble the engine with fresh parts too. As with everything though, there is obviously a tradeoff between paying an expert to do a job versus taking the time to do it yourself. Not to mention if you are more comfortable trusting the work of an expert, versus perhaps another person thinking nobody will take more care with an aircraft's engine than they would themselves.

The succes and adoption on the Apex is based on one proprietary PSRU. Suzuki would be my choice , Arctic Cat has used them for years, but no PSRU available for them.

Watched this series. As we say in England. This was ACE.

love your videos and desire to build. One of these days ill run into you . keep up the great work. Oh and bummer about benton. super lame.

Get a borescope and leak down compression tester. Can look at pistons, cylinder walls, valves with cheap borescope for any used engine (and for tge engine u fly to see if overhaul is due). With leakdown compression set up can blow air into cylinder and listen to oil pan, exhaust and intake to see where engine is losing compression (foe used

it's possible the green gunk is what is supposed to stop leaks, and it may have worked too well. if there was an exhaust leak into the block from a bad head gasket the green gunk may well have blocked the overflow valve too causing an enormous coolant system pressure problem resulting in, among other things, the blown water pump gasket. i wouldn't be surprised if that coolant leak company defends their product in such a way. like you, i don't like the stuff... it's just a wrong-headed way to approach a fix. it may be useful for diagnosing a problem. which may have been, ironically, what happened it your case. IDK. good luck on the new engine, and like many others, i'm anxious to see what was up with the old one.

Regardless of engine choice, everyone should be able to open their engine and do a complete inspection. Including all seals and gaskets. Maybe not rebuilding the bottom end but everything else is a must for home builders. You will be a lot safer when you fully understand how your engine works. Corvair engines are definitely an excellent engine option. Leak stop of any kind is a no go. The only way that thing developed a head leak is from an air pocket causing a hot spot. Purchase a hand vacuum setup for your coolant fill and system bleeding.

So can the engine be equipped with a constant speed or even a ground adjustable prop that could give you that cross country performance. Seems like a ground adjustable would be the simplest and most economical option.

Still being able to get a factory new engine so you don’t have to guess about the condition would certainly be a benefit of the sidewinder…

What kind of back electrical power do you have for the ECU.

oh by the way, the engine has some very very small cooling passages between the exhaust valves which are now likely plugged .

Almost all new engines come from the factory with sealant in the coolant, only a problem when a head gasket fails, exposes the chemical to air and it congeales the coolant inside rather than on the outside.