I have a newer 110 Viking and have been running a 50% avgas, 50% high test. I am using avgas because I found 8 barrels of it for free. I know it's terrible crap but it was FREE. It works fine in my Lycoming. 

After 100 or so hours on it I lost compression on the center two cylinders. 

Jan suggested Marvel Mystery Oil but it is running too badly to fly so I pulled the engine and the head off and will get the valves lapped. 

Lead deposits on the valve seats caused the leak. The cylinders are perfect, still can see some honing marks so the engine isn't even properly run in yet?

So, my question is when you travel do you use avgas and how do you keep the lead off?

Did I use too much of the avgas too continuously?

As I'm pulling the engine off and apart I am impressed with the detail used in assembling this power package. 


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Viking Engines, UL Engine, Rotax and others and so forth DO NOT handle lead well at all. IF you have to use it, it should be used with Decalin. This was a question we asked you when you called and we tried to help troubleshoot your issue, you did not state what you are saying above, as in, running 50% leaded fuel rather was said that you mostly run car gas and occasionally avgas, it is very difficult to troubleshoot with the wrong information. A couple years ago as well you mentioned the use of aviation oil in your engine. It is very important to run as we recommend (as goes with all engines) or this will be a reoccurring theme. This should no means be taken as a limitation in regard to operating the engine, you just use car gas at home and bring the additive when you travel as is true with most aircraft engines. 

As far as your issues, we have not seen that lead on the valve seats is the issue, rather the lead gets up into the exhaust valve guides - this is why it was told to add a large amount of Marvel Mystery oil to the oil and the gas, try to get the engine started, and run for half an hour. This will not fix the issue, but it will lubricate the valves and create an illusion that the problem went away. By doing this, we can specify where the problem is rather than guessing. Now, it is difficult to know for sure, but a complete cylinder head rebuild should alleviate the problem. 


Thanks for the reply.

That is good advice about the valve guides. 

I removed the engine and head as I felt that was going to be the end result. 

This is the first I have heard of Decalin. I have ordered a bottle from AS. 

I am instinctively skeptical of chemical cures for mechanical faults but will take your advice.

From what you describe the valves are sticking and not closing properly.




If I may...

It's not really a mechanical fault that these engines don't react well with lead; they were designed with unleaded gas in mind

While I never had the pleasure of owning a Viking engine, I also didn't use Decalin for the first 150 or so hours in my engine (Corvair) and needed my heads rebuilt.  Since then I've used Decalin religiously and haven't experienced the same issue

The gentleman that created was friends with both Jan and WW if I recall. We spent many hours testing Marvel Mystery oil and Decalin and can tell you that Decalin DOES work - Marvel not so much for that purpose, Zenith uses it as well in their setups. Good stuff!

I have a Viking 110 engine in my 701.  

I run nothing but Ethanol free gas in my engine with 1oz of MMO/10 gal.  

Engine runs great. 

Hello John...

How many hours do you have on your Viking 110?   This question comes up from time to time on other forum sites.

I have run it about 270 hours. no problems yet.

From your comments are you using Avgas?

I have 160 hours on my Viking 110 and replaced all the valves in my engine. 

Not cheap, as an auto mechanic I used to tell customers Honda's don't break but when they do they cost the same as airplane parts. 

$550 cdn for 8 tiny little new valves. 

4 of them were so badly pitted they couldn't be re ground.

Lesson learned, don't use avgas and when I must, use Decalin.

Anybody have any thoughts or info on the new unleaded aviation fuels and Honda Viking engines?


We were early testers of a lot of those fuels, especially the SWIFT fuel. All are good to use with the Viking engine.


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