Overheating and detonation

Aircraft powered airboat discussion.
FlounderPounder
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Posts: 18
Joined: Fri Feb 09, 2018 5:03 pm

Re: Overheating and detonation

Postby FlounderPounder » Tue Feb 13, 2018 4:01 pm

Slidin Gator wrote:Flounder,
I was in the same boat as you a couple years ago, with my first AV motor. So I have been through this (and other) learning curves. I am attaching some documents that were useful to me. The timing box is useful to check the timing by yourself, otherwise you need 2 feeler gauges and a helper to move the prop.

Before doing anything on the motor, I still recommend finding a tank of 100 LL to run through the motor. If that solves the problem you will know you are on the right track here. In any case it will give you a comparison point to consider the change in performance once you get the motor tuned for pump gas.

Lycoming used 7.2 and 8.5 compression ratio pistons in the straight valve engines. Angle valve engines had 8.5 or 8.7. Higher compression ratio after market pistons are available. Lycoming rates the 7.2 for use on 80-87 octane fuel. The 8.5 is rated for 91-96 Octane and the higher compression ratio’s require 100 LL fuel. Keep in mind that Automotive fuel burns faster than Aviation fuel, backing off the timing from 25 to 20 roughly compensates for the quicker burn of auto fuel. Since Airboat engines in the South tend to run hot, I would err on the safe side of these ratings.

If the engine still has issues on 100 LL fuel, you need to check the timing and confirm that both mags are firing at the same time. If the mag timing is staggered the engine would have issues such as you describe. The mags fire when the points open. You can check this with a set of thin feeler gauges (or a business card etc.) under each point. Have someone turn the prop slowly (pull plugs to release compression first). When the points open the feeler gauges will pull free. The Timing box information attached is for a unit you can buy from aviation supply houses for about $50. With this box you can check and adjust the timing by yourself.

I suspect that the FWC boats are running low compression 540 engines to run on pump fuel. Perhaps this is why the FWC officer that gave me a safety inspection last month was stuck in his new Diamondback afterwards. He had to make the trainee get off and wiggle the grass rake to get going on dry ground.

Look at this link for details on timing, as well as Youtube for video's:
https://www.avweb.com/news/maint/184370-1.html

Great thanks


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FlounderPounder
Southern Airboat Member
Posts: 18
Joined: Fri Feb 09, 2018 5:03 pm

Re: Overheating and detonation

Postby FlounderPounder » Tue Feb 13, 2018 4:02 pm

Slidin Gator wrote:Flounder,
I was in the same boat as you a couple years ago, with my first AV motor. So I have been through this (and other) learning curves. I am attaching some documents that were useful to me. The timing box is useful to check the timing by yourself, otherwise you need 2 feeler gauges and a helper to move the prop.

Before doing anything on the motor, I still recommend finding a tank of 100 LL to run through the motor. If that solves the problem you will know you are on the right track here. In any case it will give you a comparison point to consider the change in performance once you get the motor tuned for pump gas.

Lycoming used 7.2 and 8.5 compression ratio pistons in the straight valve engines. Angle valve engines had 8.5 or 8.7. Higher compression ratio after market pistons are available. Lycoming rates the 7.2 for use on 80-87 octane fuel. The 8.5 is rated for 91-96 Octane and the higher compression ratio’s require 100 LL fuel. Keep in mind that Automotive fuel burns faster than Aviation fuel, backing off the timing from 25 to 20 roughly compensates for the quicker burn of auto fuel. Since Airboat engines in the South tend to run hot, I would err on the safe side of these ratings.

If the engine still has issues on 100 LL fuel, you need to check the timing and confirm that both mags are firing at the same time. If the mag timing is staggered the engine would have issues such as you describe. The mags fire when the points open. You can check this with a set of thin feeler gauges (or a business card etc.) under each point. Have someone turn the prop slowly (pull plugs to release compression first). When the points open the feeler gauges will pull free. The Timing box information attached is for a unit you can buy from aviation supply houses for about $50. With this box you can check and adjust the timing by yourself.

I suspect that the FWC boats are running low compression 540 engines to run on pump fuel. Perhaps this is why the FWC officer that gave me a safety inspection last month was stuck in his new Diamondback afterwards. He had to make the trainee get off and wiggle the grass rake to get going on dry ground.

Look at this link for details on timing, as well as Youtube for video's:
https://www.avweb.com/news/maint/184370-1.html

Great thanks


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FlounderPounder
Southern Airboat Member
Posts: 18
Joined: Fri Feb 09, 2018 5:03 pm

Re: Overheating and detonation

Postby FlounderPounder » Tue Feb 13, 2018 4:15 pm

FlounderPounder wrote:
Slidin Gator wrote:Flounder,
I was in the same boat as you a couple years ago, with my first AV motor. So I have been through this (and other) learning curves. I am attaching some documents that were useful to me. The timing box is useful to check the timing by yourself, otherwise you need 2 feeler gauges and a helper to move the prop.

Before doing anything on the motor, I still recommend finding a tank of 100 LL to run through the motor. If that solves the problem you will know you are on the right track here. In any case it will give you a comparison point to consider the change in performance once you get the motor tuned for pump gas.

Lycoming used 7.2 and 8.5 compression ratio pistons in the straight valve engines. Angle valve engines had 8.5 or 8.7. Higher compression ratio after market pistons are available. Lycoming rates the 7.2 for use on 80-87 octane fuel. The 8.5 is rated for 91-96 Octane and the higher compression ratio’s require 100 LL fuel. Keep in mind that Automotive fuel burns faster than Aviation fuel, backing off the timing from 25 to 20 roughly compensates for the quicker burn of auto fuel. Since Airboat engines in the South tend to run hot, I would err on the safe side of these ratings.

If the engine still has issues on 100 LL fuel, you need to check the timing and confirm that both mags are firing at the same time. If the mag timing is staggered the engine would have issues such as you describe. The mags fire when the points open. You can check this with a set of thin feeler gauges (or a business card etc.) under each point. Have someone turn the prop slowly (pull plugs to release compression first). When the points open the feeler gauges will pull free. The Timing box information attached is for a unit you can buy from aviation supply houses for about $50. With this box you can check and adjust the timing by yourself.

I suspect that the FWC boats are running low compression 540 engines to run on pump fuel. Perhaps this is why the FWC officer that gave me a safety inspection last month was stuck in his new Diamondback afterwards. He had to make the trainee get off and wiggle the grass rake to get going on dry ground.

Look at this link for details on timing, as well as Youtube for video's:
https://www.avweb.com/news/maint/184370-1.html

Great thanks


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Well found out some more info, visited with my buddy I got it from, he had the same issue on his boat so he timed the mags by “ear” so pretty sure they are not synchronized. Then got home and started it up and found #1 bottom and # 4 top plugs are not firing. Before I make any changes I’m going too change plugs and oil and clean the points in the mags and reset the timing to 25deg. Another friend of mine is also allowing me to use his tale numb to get AV fuel at the airport. I’ll post more when I find more out... and was told that the numbers on the block are not corresponding with the angle valve heads and cylinder and piston size that’s on it. So more research, but the damn thing pushes the **** out of boat.


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digginfool
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Re: Overheating and detonation

Postby digginfool » Tue Feb 13, 2018 5:06 pm

FlounderPounder wrote:Not running av gas, can’t buy it down here without a tail number of a plane is what I was told by the local airport. My timing light won’t be in for a couple of days and it is to cold too pittle with for a couple of days


Nothing for nothing but you could just pick an N number from a plane sitting on the ramp. Make one up. Look up pictures on the internet and pick one. Pretty simple solution. One of the self-serve pumps at our airport requires an N number. I give it a partial, made-up number. N182
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

Uhairball
Southern Airboat Member
Posts: 285
Joined: Mon Aug 15, 2011 6:31 am
Location: Inverness, FL

Re: Overheating and detonation

Postby Uhairball » Tue Feb 13, 2018 5:39 pm

try using A1.

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mojoe
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Joined: Thu Jul 23, 2009 8:55 pm
Location: Catfish Motel

Re: Overheating and detonation

Postby mojoe » Tue Feb 13, 2018 7:44 pm

OU812

Classic
Airboating is like marriage: There are unlimited ways a person can be right, and somehow still be wrong at the same time!!

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Slidin Gator
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Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: Overheating and detonation

Postby Slidin Gator » Tue Feb 13, 2018 8:03 pm

Flounder,
I agree with that plan, particularly using a buddies tail number (or a made up one as suggested). At $500+ per cylinder, AV gas is pretty cheap in my book! Getting it is the hassle. I do keep a couple of bottles of Octane boost and lead substitute in the boat, just in case I need to bum fuel from someone, but I have never used it. Did the previous owner run AV gas or pump gas and did it run good for him at some time before acting up?

I have timed many engines by ear, but I have no idea how you could synchronize two ignition systems by ear. Assuming your engine is wired to aviation specs, the #1 Bottom and #4 Top (and vice versa) are on the same mag. That should be the mag on the STBD side of the boat and it should also be your impulse/starting mag. There are lot's of other ways to wire them, but that is matches aviation specs. My guess at this point is a bad mag or harness (and probably poor synchronization, and wrong fuel...).

The interesting thing about this subject is that anything to do with mags is off limits to pilots in FAA certified applications. Any work or adjustments have to be done by a certified mechanic. So the pilots don't talk about mags or timing on the aviation websites, either because they don't know anything or they don't want to talk about what they have done.

Most of what I have learned about mags has come from this website (in particular the posts from GMAC76), plus some hot rod aviation sites and hands on.

What type of a harness do you have (automotive or aviation plugs and wires?). Are the wires solid copper core or resistance type? They should be solid copper but it is possible/likely that they are carbon core, resistor type. Pull the wire harnesses off and check them with an ohm meter, they should read very low ohms, just length dependent. Figure out what type of mags you have (or post a picture) and download the manual from the previously posted links for details of other mag checks you can make with an ohm meter to confirm the distributor has good continuity. Also, do not take a file to the points without reading and understanding the mag manual.

There is also the possibility that the spark is leaking and jumping to ground through the wires or in the Mag. Look for bad wires and insulator parts in the mag etc...
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540. A Bob Stossel original, still running strong.

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Planeguy
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Re: Overheating and detonation

Postby Planeguy » Tue Feb 13, 2018 11:19 pm

If the O-360 is stock it should run fine on premium unleaded. Aircraft have been doing it for years and the day is coming when we won't have a choice. Avoid alcohol ruined fuels if possible. Alcohol absorbs moisture and as a result can cause severe corrosion issues with aluminum.

If you want to buy avgas, go to an airport with a self service pump and enter a bogus registration number (N1234 for example) when it asks for it. I do it all the time to get fuel for my airplane and no one has ever asked what I am doing. Talking to airport personnel who don't know you will almost never get you avgas to put in a container even if you have a legitimate "N" number.

If both mags have impulse couplers then they can be timed pretty close without a light. The impulse coupler should make the mag fire real close to top dead center. Otherwise, it is better to use a light and do it correctly. If using automotive ignition leads an automotive light should work okay if you can see the timing marks with the prop spinning. I believe the shielding on an aircraft harness may cause problems when using an induction light. If using an aircraft timing light the impulse coupler needs to "snap" before timing can be checked or set and the mags need to be "hot" so pull the plugs before you do it. Not all aircraft engines installed on boats will have impulse couplers.

FlounderPounder
Southern Airboat Member
Posts: 18
Joined: Fri Feb 09, 2018 5:03 pm

Re: Overheating and detonation

Postby FlounderPounder » Wed Feb 14, 2018 10:06 am

Slidin Gator wrote:Flounder,
I agree with that plan, particularly using a buddies tail number (or a made up one as suggested). At $500+ per cylinder, AV gas is pretty cheap in my book! Getting it is the hassle. I do keep a couple of bottles of Octane boost and lead substitute in the boat, just in case I need to bum fuel from someone, but I have never used it. Did the previous owner run AV gas or pump gas and did it run good for him at some time before acting up?

I have timed many engines by ear, but I have no idea how you could synchronize two ignition systems by ear. Assuming your engine is wired to aviation specs, the #1 Bottom and #4 Top (and vice versa) are on the same mag. That should be the mag on the STBD side of the boat and it should also be your impulse/starting mag. There are lot's of other ways to wire them, but that is matches aviation specs. My guess at this point is a bad mag or harness (and probably poor synchronization, and wrong fuel...).

The interesting thing about this subject is that anything to do with mags is off limits to pilots in FAA certified applications. Any work or adjustments have to be done by a certified mechanic. So the pilots don't talk about mags or timing on the aviation websites, either because they don't know anything or they don't want to talk about what they have done.

Most of what I have learned about mags has come from this website (in particular the posts from GMAC76), plus some hot rod aviation sites and hands on.

What type of a harness do you have (automotive or aviation plugs and wires?). Are the wires solid copper core or resistance type? They should be solid copper but it is possible/likely that they are carbon core, resistor type. Pull the wire harnesses off and check them with an ohm meter, they should read very low ohms, just length dependent. Figure out what type of mags you have (or post a picture) and download the manual from the previously posted links for details of other mag checks you can make with an ohm meter to confirm the distributor has good continuity. Also, do not take a file to the points without reading and understanding the mag manual.

There is also the possibility that the spark is leaking and jumping to ground through the wires or in the Mag. Look for bad wires and insulator parts in the mag etc...

Oil and plug preferred?


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