# GM 3.6L variants FYI

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#### Winginitt

##### Well-Known Member
Early top OH and cam changes in Lycomings are almost certainly a result of operator error. Treated properly, cooled adequately and flown often, a Lycoming will go WAY past TBO with nothing more than routine oil changes.

Reply: Agree . There is a whole industry built around supplying replacement cylinders. So early replacement is a major consideration to owners of aircraft engines. No real data check on my part, but would hazard a guess that 30/50% of owners do actually replace at least one cylinder prior to TBO no matter what type of airplane the engine is in. I think the biggest key is regular use.

[QUOTE="Toobuilder, post: 487108, member: 6803"
There is also nothing wrong with installing a good used cylinder (or a whole set) to replace bad ones. Just so long as it's documented as a"repair" and not an "overhaul".

Reply: Agree. My point, which I didn't make very well was that in order to save money, an individual might purchase a used cylinder and install it on a certified airplane himself and put no entry in the log book. Definitely illegal Maybe he just wants to sell the airplane and figures he can do an adequate job.........no harm/no foul as far as he is concerned. Big Trouble if anyone finds out though. I have seen things like that.

Going to the homebuilt/noncertified.Same guy, same engine, experimental airplane. Same guy does the same thing to same engine with same cylinder.......but does not tell the AP who performed the last inspection. He also doesn't record it in the non-required engine log book even though he uses that for documentation. Engine is running fine at yearly inspection and everything appears normal as it did when the AP performed last years inspection. The fly in the ointment here is that used cylinder was one that was replaced because of a factory defect. It sat on a shelf in a corner and was forgotten. The owner of the cylinder(s) passes away and his heir has an estate sale to get rid of all those old aircraft parts that were in the shop. Someone buys them and they look like they are good cylinders wear wise, so he sells them on Craigslist. No one is aware that this cylinder has a defect, and it gets installed on the experimental engine. Compression tests are normal.

In this case, no one did anything illegal, and money was saved.......tick...tick...tick
. Click above on "Toobuilder post " to see complete reply

What you said is correct, but with thousands of used engines in not just RVs, but other types of homebuilts as well, I'm reasonably confident that there are a lot of decisions made relative to engine maintenance where money causes less than optimal decisions to be made. Its true that it takes a lot more effort to adapt an alternative engine. A successful conversion places the owner/builder in a position where he can deal with any problems himself and usually at a very reasonable cost. What I would like to see here on this thread is a bunch of knowledgeable people discuss with the OP possible ways to make his project work for him rather than just tell him it won't work. When the variable cam timing was introduced, its purpose was to increase economy and help with emission control. Then the hot rod industry got involved and found ways to actually make it help produce more HP (or was it Torque). So maybe instead of saying it won't work well, and just attacking that....maybe we might encourage him to try and keep us posted on his results. Its not like he can't disable or remove it if it doesn't test out well for him.

#### BJC

##### Well-Known Member
HBA Supporter
Ron W:

Do you have data that could be used to compare engine failures in E-AB with similarly powered type certificated aircraft?

Thanks,

BJC

#### pictsidhe

##### Well-Known Member
The issue is not that VVT doesn't work, it is that is has zero benefit and several negatives when applied to aero engines. it will not give extra power, the extra economy only during taxi. I'd be surprised if the fuel saved per flight weighed more than the VVT bits. The 3.6 has a lot of inapplicable technology for aero use. That weighs it down and is more to go wrong.

Seriously, the best way forward is to switch from the DOHC VVT DI 3.6 to the bigger, lighter and torquier aluminium 4.3 OHV engine. The new 4.3 is 3/4 of an LT. It will weigh less and give more power at a piston speed that will give a decent life and reasonable economy. It's probably cheaper, too. If the success of the numerous LS conversions are anything to go by, a 4.3 is likely to work well. A LS redrive will bolt straight on, though it will likely need tweaking. That way the OP still gets to use a modern GM car engine for which redrives are nearly ready made. The 3.6 is just the wrong engine to convert.

#### rv7charlie

##### Well-Known Member
Problem with the typical GM 4.3 V-6 is it's a 90* V instead of 60*. Various monkey motion, depending on version, attempting to compensate for its imbalance, all of which add weight & don't fully cure the 90* problem. And things may have changed, but aluminum blocks for the 4.3 motors used to be hideously expensive and meant you couldn't affordably purchase a crate motor.

#### pictsidhe

##### Well-Known Member
Yes, the 90 V6s are offset crankpin with a balance shaft. The 60 degree engines just have offset pins. GM has been making aluminium 4.3s derived from the V8 LTs since 2014. They are 2 valve ohv, but do have VVT and DI. The VVT is fairly easy to remove, I don't know about the DI, but suspect that it is a bit more work. I bet that Ross could build a port injected 4.3 system, though.

#### Winginitt

##### Well-Known Member
The "old"4.3 was used successfully in many conversions with reduction drives. The newer version is actually a different engine with the same displacement.
The original 4.3 had 3 different crankshafts. There was an even-fire with 120 degree firing cycles. Next was a semi-evenfire with 132/108 degree cycles. Both used a crankshaft with offset journals on each throw. Last was an odd-fire crankshaft for racing that had 150/90 degree timing events. Some engines used a balance shaft to counter natural imbalance in the engine. Many were successfully used for conversions usually employing a reduction drive. Haven't seen any of the newer (but different) 4.3 engines used in conversions yet. Don't know what the crankshaft configuretion is in the new version, but suspect its not the stronger but odd fire with no offset on the journals.
Lots of considerations when adapting a V6 as an alternative engine.

#### pictsidhe

##### Well-Known Member
The 4.3s have been even fire in production vehicles since the 80s. People didn't like the 'broken' sound. They went even fire before they gained a balancer. My '92 truck has an even fire non balancer iron 4.3

#### Winginitt

##### Well-Known Member

Corvair engines had a problem with crankshaft breakage because of poorly ground (small) radii on crankshaft journals. Many 4.3s have been used successfully in aircraft conversions,most with reduction drives. I don't know how GM is handling the configuretion of their crankshafts on the new versions but suspect they may be employing this same technology. Anyone know for sure?
When this type of crank is employed, a narrower bearing is used to allow room for the separating surface. All these things contribute to a weaker crankshaft, but as I said....there were a lot of successful 4.3 conversions.

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#### pictsidhe

##### Well-Known Member
An even fire 4.3 crank has less offset between journals than a 60 degree engine crank. It will be stronger than the 60. The fact that neither cranks tend to break should be good enough for anyone wanting to use any of these engines. Yes, you could get an odd fire crank ground, but you better check with your redrive man first. He will scowl at you...

Incorrect fillet radii will kill any engine. It's why you need to be so careful having a factory crank reground or buying a custom crank. There are people who can grind them properly, and there are people who can't. Factory cranks are almost always good these days. They are affordable if made for cars, too. Many of them have rolled fillet radii to get their long lives, which is hard to do properly. 'Upgrading' from known reliable factory cranks seems silly to me. It's caused a lot of blown engines...

#### mm4440

##### Well-Known Member
The split throw cranks used to make even an firing 90 degree V-6 may be strong enough. A 60 degree V-6 has a crank designed for 6 throws not one improvised for production on V-8 tooling. If GM had made an aluminum version of their 60 degree pushrod V-6 it would have been great for conversion; light and compact. A Rover 4.6 l. Buick derived V-8 would be my choice over a V-6 if an LS based V-8 is too much engine for an airframe.

#### Winginitt

##### Well-Known Member
The split throw cranks used to make even an firing 90 degree V-6 may be strong enough. A 60 degree V-6 has a crank designed for 6 throws not one improvised for production on V-8 tooling. If GM had made an aluminum version of their 60 degree pushrod V-6 it would have been great for conversion; light and compact. A Rover 4.6 l. Buick derived V-8 would be my choice over a V-6 if an LS based V-8 is too much engine for an airframe.
That was my thought too. Had a Rover 4.2 and a 4.6 in the shop but sold them. There is a lot that can be done with them by mixing and matching parts from different versions. Even had 2 Buick 300 crankshafts. The problem with the 4.6 is that the aluminum between the liners is kinda thin and some of them develop a problem with a leak between the aluminum and the liner that some people mistake for a blown headgasket. It can be repaired with a new liner but its hard to find someone who can do it. Although the liners are produced in the US by a quality mfg, a company in England has some kind of control over their sale. I still think they make a great engine conversion for anyone willing to work it out.

#### mm4440

##### Well-Known Member
The replacement sleeves with a step on top are available from Darton, LA Sleeve and others. I do not know if Darton has a MIDI sleeve for the Rover, BOP v-8s. It is a wet sleeve conversion.

#### pfarber

##### Well-Known Member
HBA Supporter
The Lycontisaurs work. That's why they are the most common engine in GA. If they sucked, like some of their old competitors did, they would have died out to be replaced by something better. That something hasn't come along yet, though Rotax has gained a toehold. I say this as someone working on an alternative engine project.
Sorry, but nope.

You cannot simply bolt an motor X to a certified plane and go off with it. That's the reason why lyc' and cont's still exist. They have a build in monopoly backed by the FAA. GA motors SUCK. The parts are expensive because they WANT them to be. I can get a custom forged crankshaft built to spec for $2k. Yet a certified cranks is$8k simply because I can't stamp that Lycoming part number on the box.

Why a 7.5:1 compression motor is still running on 100LL is a mystery. Almost every one can get a paper STC for Mogas and run just as well. Hardened valve seats have been a thing for decades.

How many Billions has Ford/Chevy/Toyota vs Lyc/Cont put into engine development vs etc yet people think that the certified engine is more reliable... they never realize that they can literally drive their car every day for months and never touch it except for gas.

Sorry, but the tired old wifes tale of aviation motors being the shiznitz are just that... tired old wives tales.

#### Winginitt

##### Well-Known Member
I don't think anyone on HBA would characterize me as being a staunch supporter of certified airplane engines, but I do believe aero engines that are new or properly maintained are very reliable. As everyone knows, they require more service (as a fleet, not necessarily an individual engine) in order to insure that they do stay reliable. Nothing wrong with that because of the definitive nature of flight and the out come of any failure. I admire the simplicity of the complexity......hows that for an oxymoron. They really did encompass a lot of complex problems in a very simple package.

The real problem is the cost of buying and maintaining these engines. Much more complicated and refined automotive engines and parts are manufactured daily by small niche companies that have smaller bottom lines than Lycoming. It doesn't cost anywhere near $5-8K to manufacture a replacement crankshaft. Several hundred$ for ONE exhaust valve. A complete set of "quality" connecting rods can be purchased for well under $1k for a racing engine, yet the rods coming from Lyc are somewhat crudely made and from my observation, poorly balanced. No real new technology in manufacturing a replacement aviation camshaft yet far more expensive than better quality aftermarket or oem camshafts. Valve springs require very little technology due to low rpm operation when compared to automotive counterparts. There are just so many parts for aero engines that are excessively priced for the ancient technology they employ. If realistic prices were available, there would be little need for alternative engines. Sure there are certain components like Cylinders that may have justifiable prices, but then you look at the price of a few rubber motor mounts and just shrug...... The main problem with aero engines is "cost". Then "cost" affects continued reliability decisions. #### BJC ##### Well-Known Member HBA Supporter The real problem is the cost of buying and maintaining these engines. It would be informative to learn the actual FWF purchase and install costs for auto conversions in the 180 to 210 HP range, for comparison with experimental 4 cylinder Lycoming and clone engines. Anyone here willing to share some real been there done that numbers? Thanks, BJC #### Winginitt ##### Well-Known Member It would be informative to learn the actual FWF purchase and install costs for auto conversions in the 180 to 210 HP range, for comparison with experimental 4 cylinder Lycoming and clone engines. Anyone here willing to share some real been there done that numbers? Thanks, BJC That sounds like a good place for Ross Farnham to jump in and let us know the basic cost to buy and install a Sube conversion in an airplane. He has two examples of alternate engine conversions. But why cherry pick? You could compare the cost of an O200 or O235 to the Corvair conversions ? Then there are the Buick/Olds/Rover conversions and even V6 Chevy and Ford. Might even take a look at the V8 Ford that Ben Hass built. Lots of info on the internet if you want to look for it. Why not put some substantive information up and let us analyze what you found for a change? If you believe that used aero engine owners buy and operate more cheaply than conversion builders, tell us about the things you do and the costs you incurred over your last 10 years or so of owning and operating. Compare your actual costs to what Ross has spent for basic conversion and subsequent operation and maintainance. That way you have two intelligent and capable people who chose opposing paths to flying providing contrasting data. It would be interesting to see that comparison. Don't fudge though...... #### wsimpso1 ##### Super Moderator Staff member Log Member All this talk about compression ratio and engine rpm and specific output... In airplanes, WEIGHT IS THE ENEMY. Weight of the engine and weight of the fuel load to fly our missions are crucial. We have two really important metrics built around this issue that are more important than any others for engines: Pounds per HP Expressed and Specific Fuel Usage Pounds per HP Expressed - this is pounds of engine, coolers, duct work, induction, exhaust, gearboxes, fluids, and prop divided by horsepower expressed in air moving aft off the propellor. This takes into effect not only how much power the engine makes and how much weight we have to lift to altitude and control with wings and tail, but also how good we are at turning the power into thrust. This is important - the faster we turn the prop, the smaller it has to be to stay sub-sonic, the less static thrust it can generate per horsepower, and more inefficiencies you get from moving the air around the powerplant and fuselage. Specific Fuel Usage - This is the amount of fuel per hour per horsepower generated at cruise speed - because a huge fraction of our fuel burn is in cruise. It matters because the higher this is, the more fuel we have to lift to altitude and control with wings and tail to fly our mission. The combination of total engine weight and fuel load at takeoff have huge influence on everything in design of the airplane that uses the engine. When a VVT-DI automotive engine as installed for flight plus its fuel load for four hour missions is lighter at the same cruise horsepower and altitude as the equivalent airplane engine, we can talk about how you got there. There are some big reasons that so many homebuilts are running the traditional airplane engines: • We can install the traditional airplane engines and they function reliably as intended. Auto conversions with high compression ratios, direct injection, variable valve timing, etc being proposed are NOT available as turn key systems. Right now we are only promised firewall forward engine kits with fixed valve timing and port fuel injection in the 200+ horsepower range; • We can run them on reasonable fuel burns. With cylinder tunable port fuel injection and electronic ignition like SDS offers, you can get below 0.40 lb/hp/hr at cruise power levels in traditional airplane engines. Automotive conversions make similar fuel specifics at the fuel island (1800-2000 rpm), but see where you are on the specific fuel burn map at twice that engine speed (typical cruise power settings) - it is generally quite a bit higher fuel burn. To have one of these newer VVT-DI-HighCR engines, the individual has to develop the engine, installation, and systems, then debug and make it reliable. No companies are doing it yet. Now maybe the folks on here telling us better engines will come from these VVT-DI engines with high CR's can prove it to us by developing and marketing to us better engines than we can currently get... I would love to see it. I might even send a deposit to hold my place in the delivery sequence. But I am not holding my breath. Billski Last edited: #### rv6ejguy ##### Well-Known Member My entire FWF package including engine, prop, PSRU, EFI, turbo system, rads, engine mount etc. cost$9500US in 2003 dollars. So people who say it will always cost more than a certified engine- no. I have lots of other customers flying auto conversion for many years as well who've spent a fraction of the money (but maybe lots of their time) compared to a Lycoming.

IMO Russell Sherwood's EG33 Glasair is perhaps the most successful of all auto conversions on the basis of performance, weight, cost and demonstrated reliability and durability. You new folks and non-believers can search the threads for his name here. He's repeatedly kicked the butts of all other Lycomings and Continental powered aircraft in his SARL class over a number of years as proof of that power and reliability. I believe his has close to 700 flight hours on it now.

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#### rv7charlie

##### Well-Known Member
My numbers are skewed a bit, because I got the core engine, the reduction drive, and the controller at a significant discount from a friend who changed direction. But even with 'retail' parts in today's dollars, my total cost (Mazda Renesis, RWS reduction & controller) would be similar to Ross' numbers. I'd expect any decent conversion in the 150-200 HP range to total in the $10k-$15K range, depending on used vs crate engine. I'd consider a reasonable rule of thumb would be to add your core engine and reduction drive costs, and double it for your total installed cost. And take the typical 1st timer traditional engine installer time, and multiply by at least a factor of 10. Reason for both is that unless you're an absolute genius *and* have engineering chops, you're going to do most things around the engine at least twice, often 3 or 4 times, before it's 'done'.

Charlie

#### pictsidhe

##### Well-Known Member
I dunno, I'm pretty good at engineering stuff. But unless it's something I've already done, there's a good chance it will take me more than one go. Especially when I am trying to cram a quart into a pint pot. But, I have enougb practice to know what is probably going to give me headaches.

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