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Modification of 160 HP Wide Deck

99C5Pilot

99C5Pilot

SPONSOR
Wasilla Alaska
Looking at purchasing a Super Cub. It has a Wide Deck 0-320 that is legally upgraded to 160HP. When doing it they also pumped up the compression to 10:1. Any concerns on 10:1 compression on a legal 160HP 0-320 wide Deck? Has low hours, under 300 on motor SMOH.
 
Don't know of an STC for 10 to 1 pistons. 8.5 to 1 is standard for the 160.

Posted Using the Free SuperCub.Org Android App!
 
Interesting, but I would second Steve. Check the paperwork because it does not seem very likely to be legal.
Also I would not recommend auto fuel at that compression ratio.
If you are thinking about buying it, find out how much a new top end would cost to make it legal. Deduct that from the asking price. Then ask, what else they have done that is not up to snuff.

My opinion, without knowing anything about this

Bill
 
Agree, I know it is not legal but wondering what the ramifications are of purchasing a super cub with 10:1 pistons knowing this? Insurance going to be an issue? Has anyone heard of any known issues with engine life due to the 10:1 pistons? I was told you have to run AV Fuel in it due to the 10:1. Thanks everyone for your thoughts and opinions. Learning a lot from being on this forum. Any other opinions welcomed.
 
Long as you run avgas I have not heard anything bad about 10 to 1. In fact, what I have heard is pretty much all good.

Bill
 
Know of several with 10 to 1 that are experimental with no issues, all fairly new though. I would guess more pressure means more heat and less longevity.

Have not seen an insurance adjuster tear and engine down but if they had a reason...
 
Thanks again everyone and appreciate the feedback. This is helpful and just wanted to read if there were any known issues other than not being legal and having to run AV Fuel. Planning to put it on floats in the summer.
 
Steve Tubbs Performance Air in Caldwell ID has lots of experience with 0-320's and mods and making TBO.
All for exp. engines.
 
Last edited:
99C5Pilot said:
Looking at purchasing a Super Cub. It has a Wide Deck 0-320 that is legally upgraded to 160HP. When doing it they also pumped up the compression to 10:1. Any concerns on 10:1 compression on a legal 160HP 0-320 wide Deck? Has low hours, under 300 on motor SMOH.
Click to expand...


Perhaps you have already done so but have your mechanic do a pre-buy inspection and let him know about the 10:1 pistons. Unless this is experimental, he should be telling you to walk / run away from it. If he doesn’t tell you this, then ask him if he is willing to do your annuals for you.... from now on.

If I were to knowingly annual an airplane with a unapproved modification (especially one of this nature) I would be pretty much be kissing my license goodbye. Not to mention assuming a huge amount of liability.

How did you find out that it had 10:1 pistons in it?

A "legal" 160 hp O-320 does not have these installed..... They use the 75089 piston @ 8.5:1
 
I 2nd cubpilot2, the 160hp does fine with 8.5:1. Now that you spilled the beans, you should walk away. The ANC FSDO will be tracking your every move.....
 
dalec said:
And he is a very reputable character :lol:
Click to expand...

As far as cousins go, he's alright.:lol:

As far as walking away from this plane?? Unless you have black helicopters hovering overhead, I would think it simple enough to put a set of certified pitons in and use a bowl the next time you have beans.;-)

Jerry
 
the insurance company won't check.... but the NTSB will if you have any kind incident that might involve the engine... read some accident reports. then the insurance company will know
 
Buy it and put legal pistons in it! A friend of mine tried this then got cold feet when he realized the liability concern. Don't give your insurance company a good reason to walk away just when you need them most.
 
Call Loren at Ly-con. They ship cylinders with 10:1 everyday! Not legal on certified, but no issues with them. They also ceramic coat the top of the pistons to kill the heat. In fact you will run a lower CHT and oil temps with a 10:1 ceramic coated over a standard non coated 8.5:1. They will tell you the same and I have seen it 1st hand. I know a "guy" that has 10:1's with a ton of hours, no issues!
 
My opinion. Once non-approved parts were installed that engine became experimental by default. To return it to airworthiness on a certificated airplane will require more than replacing the pistons. It'll require a complete tear-down and reassembly with inspected/re certified parts using Lycoming assembly procedures and standards. It isn't any different from any other engine that crossed the line into the experimental category, whether using certified parts or not. Once experimental it's not simple to return it to certificated service. In my opinion, while the Supercub in question may be the nicest airplane on the market, if it does not have a specific FAA approval for the high compression pistons? The airplane does not have a legal engine and will require a major overhaul to restore that engine to airworthy condition. I'd seek an opinion from Joe Norris to confirm my interpretation but I'm not the one buying the airplane. If I'm mistaken I welcome others to correct me. Good luck with your search.

For the record, I have no issue with high compression engines. That really isn't the issue here. Know the rules. Buy smart.

SB the Lurker.
 
Last edited:
sierra bravo said:
My opinion. Once non-approved parts were installed that engine became experimental by default. To return it to airworthiness on a certificated airplane will require more than replacing the pistons. It'll require a complete tear-down and reassembly with inspected/re certified parts using Lycoming assembly procedures and standards. It isn't any different from any other engine that crossed the line into the experimental category, whether using certified parts or not. Once experimental it's not simple to return it to certificated service. In my opinion, while the Supercub in question may be the nicest airplane on the market, if it does not have a specific FAA approval for the high compression pistons? The airplane does not have a legal engine and will require a major overhaul to restore that engine to airworthy condition. I'd seek an opinion from Joe Norris to confirm my interpretation but I'm not the one buying the airplane. If I'm mistaken I welcome others to correct me. Good luck with your search.

For the record, I have no issue with high compression engines. That really isn't the issue here. Know the rules. Buy smart.

SB the Lurker.
Click to expand...

Agreed. The guy trashed it. All for nothing. Opinion (I did not write the law)
 
beezerboy said:
the insurance company won't check.... but the NTSB will if you have any kind incident that might involve the engine... read some accident reports. then the insurance company will know
Click to expand...

Threw a rod and landed in a field around a tree on upside down, no one came, FAA or NTSB. Not long ago.

As far as the pistons go let your concience be your guide. ;)
 
Steve Pierce said:
Threw a rod and landed in a field around a tree on upside down, no one came, FAA or NTSB. Not long ago.

As far as the pistons go let your concience be your guide. ;)
Click to expand...
Yea but my guess is when they looked your name up "run away, run away" was heard throughout regulatory land, me I drew and audience?
 
A C206 seaplane lost power on take-off, nothing happened, plenty of water. Tower at PHNL called it in, AD was missing in logs, IA suspended. Nobody hurt and nothing bent.
 
Great thoughts and this is what I was wanting. I wanted to know what I was getting myself into with this type of a modification. Owner told me that they put the 10:1 pistons in it and was upfront about it. I won't give a tail number or names!! Based on this thread I am glad I did not give more information as I would not want the seller to have an issue. I am sure for some it is not an issue but I want to make sure that when spending this kind of money I am not going to have issues if I ever decide to re-sell. Appears that I would need to find the right buyer and have them with a mechanic that would turn a blind eye on the 10:1 mod if I decided to re-sell it. Could end up being a loss for me.... I believe that to be too big of a risk for me to take. It is a low time beautiful cub with great performance..... But.....
 
99C5Pilot said:
Great thoughts and this is what I was wanting. I wanted to know what I was getting myself into with this type of a modification. Owner told me that they put the 10:1 pistons in it and was upfront about it. I won't give a tail number or names!! Based on this thread I am glad I did not give more information as I would not want the seller to have an issue. I am sure for some it is not an issue but I want to make sure that when spending this kind of money I am not going to have issues if I ever decide to re-sell. Appears that I would need to find the right buyer and have them with a mechanic that would turn a blind eye on the 10:1 mod if I decided to re-sell it. Could end up being a loss for me.... I believe that to be too big of a risk for me to take. It is a low time beautiful cub with great performance..... But.....
Click to expand...

See if the seller will put new legal cylinders on it ? I would think that would solve the problem
 
My oh my! What drama. While you are all technically correct and giving good advice, there are so many 10:1 piston jobs running around up here that you would think it was legal! Guaranteed to put a smile on your face and no real problems I know of except for a little more oil burn.
 
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