At about 45 hours I installed the upgraded gearbox in my Viking 130 powered Zenith 750 Cruzer. Jan had told me that the new gearbox would run cooler and had a new bearing to handle the turbo power levels, and since I was contemplating getting a constant speed prop, I thought the extra headroom would be worth the investment since constant speed props run higher RPMS.

I have about 15 hours on the new gearbox and I have to tell you I am surprised how cool in runs, how much cleaner the new setup is to deal with the oil changes and the elimination of the Gear Box Oil overflow and the new sight glass makes it far easier to get just the right amount of oil in and check on the color and quantity easily. 

The major differences:

1. New bearing design.

2. New filler port. Wider and with a large cap.

3. Self contained vent.

4. No overflow bottle or external tubes.

5. Sight glass to see oil level and oil color. 

6. Relocation of temperature probe to top of case.

6. My new drain plug did not have magnet on it. Not sure if that is intentional or not.

I really never perceived any problem with cooling in the original gearbox and the only issues I had had before was I had once inadvertently overfilled the GB with oil once because I was worried about not getting enough and had added extra to the overflow, that flowed to the gearbox on a hot day while sitting between flights. I then had high oil temps on takeoff return to the airport and changed the oil and found I had put 12 ounces instead of the 6.The temps returned to normal on the next takeoff. With the new gearbox, this situation would have been entirely avoided since I could see the levels, and I have no prospect of overflow oil coming back in, or oil migrating to the overflow.

The one thing I really notice is the gearbox oil temperatures are so well controlled on the new box that during the oil changes the oil looks almost as good as when I put it in. On the old gearbox it would always come out darker.

I have no regrets springing for the new upgrade. It was well worth the time and effort and has given me even more confidence int what I already considered an excellent power plant. 

Jonathan Fay


New larger fill cap.

Sight glass.

No overflow!

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Great write up thanks.   I upgraded to the HD gearbox too.  I am very happy with it  but ... full disclosure, I don't have a lot of hours on it, may be only 5 hours on ground run ups.    I have it on my RV6A Honda project (engine not viking) and I am still in the building process.   I really like the site glass in the new gearbox and the venting system is a real improvement. 


At about 15 hours I posted a review of the updated gearbox and I was very happy with the purchase. I knew I was purchasing an updated product that had not had the same level of flight experience as the original 130 gearbox but had desirable design changes. On of the changes, the removal of the oil overflow and 5 oz oil level may have had unintended consequence that Viking has now decided to reverse due to an issue I experienced last week.
While on a short flight at nearly full power I was in the 45 for my home airport at pattern altitude when the the engine suddenly began to run rough, there was a reduction in power and the gear box temperature shot up past the max limit. I though it might be fuel and switched to both tanks without any effect. Hal pointed out the gearbox temperature and we both smelled a oil burning smell at that time. I reduced power to where it seemed sustainable and running less rough and asked aircraft in the pattern to give me priority to make a short base and final. I was able to land safely without further incident. 
After landing I was able to taxi under my own power to the hangar and I put the airplane away and took off the cowling and inspected the situation. I contacted Jan who was on vacation and he got back with me and told me to overnight the gearbox at his expense, and they would overnight a new one when they returned to Florida. I emptied the gearbox and found metal soup. There was so much metal I could hardly drain the oil.
I tested the engine without the gearbox and it ran smooth and appeared to have no ill effects, so the issue was isolated to the gearbox. When Jan got the gearbox he sent me snapshots as he disassembled and analyzed the bearings and found that with the 5 Oz oil level the bearing appeared to not getting adequate lubrication. While he could not rule out a frozen ball, or a manufacturing defect in the bearing, for safety sake he believed it was best to back to the oil overflow and 8oz. 
There are a couple of thinks that really amazed me about this whole situation. This first is that the gearbox was still producing power even with huge chunks of metal being ground down in the gears. The photos of the gearbox showed the teeth did not seem to have been effected or broken. If I had been in cruse over the mountains, while it still would have been constituted an emergency, I was making enough power to limp into a airfield and make a landing.
The second thing that really impressed me was that my Thursday my plane was ready to fly again with a fresh gearbox and while we revered back to 8oz and a overflow reservoir. Viking and Jan really stood behind the product. 
One of the things that had concerned me about flying any engine with a gearbox or reduction unit, Rotax, Viking or whatever, was what happens if the gearbox fails? Having experienced a complete internal disassembly or a bearing cage and seeing the propeller still put out enough power to limp home with has given me a lot more confidence in the design. This is one bad-ass gearbox.
The true measure of a company or person is not how well they do when the going is good, but how well they stick with out when it really costs them. This is the kind of customer support that I would love to see in all the products I buy. I am truly impressed by the how well Viking stands behind its customers and products. 
I would not intentionally put myself thru a situation like this, but having gone thru this I have no regrets. When you buy a product you have not used it's based on faith. When you have a near worst case scenario, and still end up having a good outcome your confidences is no longer based on faith but on experience with the product and the company. I have confidence I am working with a company that tries to do the right thing, constantly improves their products and is willing to learn from their mistakes.
I will continue to report on my experiences as I build more time in the replacement gearbox. I certainly recommend using the overflow and the original oil levels rather than the new pop-off valve if you are going to use the 'turbo' gearbox.

Jonathan, I followed your gearbox write-up with interest and appreciate the updates.  

What you refer to as an "overflow" reservoir, we have always viewed simply as a "fill and vent" reservoir, not overflow.   In my opinion, the fill/vent reservoir offers better venting and easier oil changes.  During oil changes, we simply add a measured amount of new oil to the reservoir, and walk away.  

As for gearbox oil level, we used 16oz for the first 15-20 hours without having high temperatures, typically around 130ºf.  Then, last March we decreased the oil level to 8oz and found the temperature is still in the same range, so that is where we leave it.  

With regard to the new gearbox, I wonder if relocating the temperature prob to its new location at the top provides a lower temperature reading?  

Curious, how does your gearbox coupling look after this event?

Given the metal gearbox, once equalibrium it reached I don't think readings are going to differ that much at various locations. I wondered that myself, but with the way the oil moves, and the metal housing, I think any difference would only be for a short while.

The coupling looked perfect, and the engine looked and sounded perfect. Jan sent me new couplings with the new gearbox out an abundance of caution so I used the new ones, but I inspected the old ones and they had no evidence of any wear or discoloring, but I am not an expert in what they should look like.

Not to beat a dead horse, which I'm known to do, but seems to me the old location at the center of gearbox will be continually in contact with oil, and the new location is not.  Without a more direct contact with gear oil, the time the new prob location senses high temps may be to late.  Just wondering.

When the failure happened we saw the temps jump to max very quickly. Without having a box with two sensors I can't prove they don't match. 

I have been reading your post's closely and I am glad you were able to make a safe landing. Although I am in the early building stages, I also plan on using the Viking 130 engine and gearbox box on my 601 HD. Happy safe flying and look forward to reading more of your updates. 


Wow, I saws the notice on Viking website to increase to 80z but I had no idea that this was the story behind the increase from 5oz to the 8oz level.  It is so good of you to share this with us.   Also great that Viking took care of the replacement quickly.  

You mentioned high gearbox temps, what temps do you normally see and how hot did it get?

Of course I now have 8oz in my gearbox.  But I have not installed the overflow catch can. (My project is still on the ground and run ups are short and not too often.)   If you have installed a catch can and it is working well for you, please post some pics for us.  

May be Jan will post some updates on the latest catch can system.  I know he had created a few different versions over time.

Thanks again.


I have 15 hours on the replacement gearbox and on the return trip from a 278 nautical mile trip (each way) trip to Idaho I was getting 145F temps on the way home cruzing at 100KTAS at 8500' at 32F OAT . On the way out to Idaho the day before it was 175F. Jan said he has seen that it drops temps at about 10 hours as it breaks in. I got temps in between the those on a trip to Mt. St. Helen's the next day but it was warmer outside air temp, lower altitude and higher power settings. It does seem that the temperature drops as it breaks in, but there is some variability with OAT, cruise speed, power and altitude, but that is expected. The graph of the temperature of the gearbox the day of the bearing failure, it was slowly climbing until the failure, then shot up to Maximum input voltage (off the scale) very quickly. I was showing a friend at work pictures of the gearbox after Jan checked in out and I was amazed after the gear had ground up all the bearing cage metal, they looked perfect. I still think I could have limped by on a reduced power setting for quite a while if I had to had I been further out from the airport. 

As to the catch can I have the plastic overflow bottle that came with the original gearbox and I just re-installed with with a new hose and L-adapter than Jan supplied with the newest gearbox. I have it mounted on the side of the engine on  bracket I created that bolts to threaded connectors on the intake plenum. Sorry I don't have pics.



Thank you for the additional info.  Funny you should mention Mt St Helens, I live near there.  I got quite a few hours flying folks up to see it.    If you ever are near KKLS I would love to see your plane.   I'd even buy the gas for a flight if you had time...

As far as temps go, I am only doing run ups on the ground but I see about 100 to 110*F on short runs.   

I know Jan had some high temp issues with the regular gear box when it was installed on the turbo engine but I don't remember what temp caused him to be concerned.   

I will get a catch can installed on my gearbox before running it much more.  



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