O-320 airbox woes

flying treeman · #1 03-08-2018, 11:36 AM

I have an O-320 that has been upgraded to a 160 Hp. As such it also has a Model MA-4SPA carb. While doing my inspection I noticed a crack in the base plate. I have read all I can on the remedies others have posted. I am in the process of having a new thicker base plate cut as we speak. For those familiar with the model carb I have to form my filter into an oval and also cut out a spot in the rim of the filter to make a fit for the accelerator pump. I am not too happy with either of these facts. I would like to know if anyone has come up with a better solution. Please help! All advice will be greatly appreciated (except to go fuel injected, ha ha) Dan

Sam Buchanan · #2 03-08-2018, 12:24 PM

I assume you have recently acquired your RV. I can't offer a 'better' solution but can tell you this method has worked well for hundreds of carbed RVs. Yes, it looks kinda crude, but it works.

My RV-6 is like yours, O-320 E2D converted to 160hp. I'm on the second filter in the 19 years I've flown it. When I replaced the filter a few years ago I too was determined to find a more elegant solution.....I ended up with the same arrangement that worked so well with the first filter. Van had no doubt been through the same thought process and decided to stay with the simple solution.

In regard to the cracked base plate, verify that there is adequate space between the cowl and airbox to allow full motion of the engine during startup and shutdown. If the cowl is making contact with the airbox, the plate will eventually crack. No contact, and the plate should last a long time.

flying treeman · #3 03-08-2018, 04:59 PM

Thanks for the input. I do have adequate clearance on the lower cowl. The airbox has about 1200 hrs. on it. From what I have heard this problem is fairly common. I just don't like deforming the filter to fit it in or having to trim out a "pocket" to fit the filter along the area where the accelerator pump sets. I was hoping for perhaps an entirely different set-up. I will stick with what I have. What is commonly used to seal along the area where the filter is trimmed, high temp RTV?

Sam Buchanan · #4 03-08-2018, 05:04 PM

Quote:

Originally Posted by flying treeman

What is commonly used to seal along the area where the filter is trimmed, high temp RTV?

That seems to be a common way of sealing around the cut-out. Try to make the seal in a way that would prevent any sealant from being sucked past the filter. I don't obsess over making a perfect seal....many early RV-3's and -4's didn't even have filters.

catmandu · #5 03-08-2018, 06:06 PM

I replaced the filter with a cut out (-3450 maybe?) on my bought flying plane with a -3322 filter. Fabricated a new plate to match it's oval shape, no cutout required. Carbed O-320 upgraded to 163.5 HP. Several hundred hours of use, no negatives to report.

AJ85WA · #6 03-08-2018, 07:19 PM

I used a aluminium spacer between the air box and carby.

But that was because my scoop was too low (360 scoop/cowl with o-320 160hp engine)

https://rv6aj.wordpress.com/2013/02/...scoop-fitting/

Vac · #7 03-10-2018, 10:24 PM

I have a couple of filters I swap out at regular intervals, same arrangement as yours. I heat them up a bit in oven before installation, which makes them much more pliable. No cut out as the heated rubber will form and seal adequately around the accelerator pump. While it?s a bit of a challenge to get the air filter installed, the nice thing about this configuration is that the base plate and internal bolts keep the filter stretched and sealed over time.

Cheers,

Vac

Vlad · #8 03-11-2018, 06:06 AM

Quote:

Originally Posted by flying treeman

I have an O-320 that has been upgraded to a 160 Hp. As such it also has a Model MA-4SPA carb. While doing my inspection I noticed a crack in the base plate. I have read all I can on the remedies others have posted. I am in the process of having a new thicker base plate cut as we speak. For those familiar with the model carb I have to form my filter into an oval and also cut out a spot in the rim of the filter to make a fit for the accelerator pump. I am not too happy with either of these facts. I would like to know if anyone has come up with a better solution. Please help! All advice will be greatly appreciated (except to go fuel injected, ha ha) Dan

What Sam said. My solution to a cracked base plate was this bracket. Still no crack 4,000 hours later. Top attaches to a sump bolt.

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flying treeman · #9 03-23-2018, 07:57 PM

I really appreciate all the input I got about my airbox. After putting on a pair of good glasses and studying the situation I realized in this case the culprit was a poor fit between the carb and the plate. There were casting areas on the carb that were not allowed for in the plate. When the plate was tightened down it put undue pressure on two areas of the plate and eventually caused cracks. I had a new plate cut and carefully fit it to the carb so that there were no high spots to cause undue strain. I believe this will fix the problem for good. Again I want to thank everyone for their time and advise. It is a pleasure to be a part of such a family. Now off to put time on my plane!