M

mlwynn

Well Known Member
Hi all,

I am busy with the FWF. I bought the VA 138 ( I think that's the right number), which is Van's firesleeved hose to go from the firewall bulkhead fitting to the engine driven pump (IO 360 M1B, if that matters). The hose is definitely very tight--hence too short. The first time I start the engine, something is going to rip out. Clearly, I need a longer hose. The question I was trying to sort out is, how much slack? If the hose is a really tight fit, is one inch longer correct or would two inches be better. How much is too much?

I mounted my oil cooler on the engine mount so there will be some differential motion there leaving me with the same question. The fuel hose from then engine driven pump to the fuel servo does not have any differential motion so I expect substantially less slack is needed there.

So, is there a good rule of thumb for sorting out slack?

Thanks,

Michael Wynn
RV 8 FWF
San Ramon, CA
 
tight hose

Michael,

I can't give you a good answer on the hose length - or rather it would be just my opinion - but I am curious if there was an error in the manufacture of the hose or if the starting point on the firewall is different from the instructions.

I had heard that if you use the Van's Lycoming IO-360-M1B and the appropriate FWF kit, everything fits perfectly. Perhaps you don't have these, which would also explain the issue.

Regards,
Mickey
 
Hose fit

Hi Mickey,

I did not, in fact, use Vans FWF kit. I am using a Sam James cowl so a bunch of things probably wouldn't fit. I am not sure why the fuel hose is short. Perhaps I mis-placed the bulkhead fitting by an inch or so. That would seem like the most likely reason.

Thanks,

Michael Wynn
 
I made all of my own hoses and just used judgement

You definitely do not want to have anything anywhere near tight in the area between the airframe and the engine. I would lean toward 2" rather than 1" of extra length. I would like to say you just look at it and you will know if it is too tight or too long - I guess that's not much help. In the wiring world where you have a similar problem, the rule for new aircraft installations of individually terminated wires when I started out as an inspector at McDonnell Aircraft was you had to be able to cut off the terminal and re-terminate three times. Every thing flexible needs a service loop, chafing protection, support and strain relief. You have to develop a feel for it and it sounds like you have started that development.

My RV-6A has around 600 hours on it and I have had one related problem. I have an 1/8" aluminum tube installed for my fuel pressure gauge. It met all of the criteria but at some point, perhaps in the original installation, I let it come in contact with a spiral shroud on an engine control cable. It wore through and was leaking fuel directly above the left exhaust pipe. I found it because I had to remove the carb heat cable to do all of the panel rearrangements needed to complete my new SL-30 NAV/COMM installation. Moisture got on my hand while I was working in that area. Even when you are very careful and know the rules things like this can happen buried down in the bowels of the power plant house when you try to squeeze you hands into tight spaces to complete a subsequent installation.

Bob Axsom
 
Hose slack?

The title led me to believe that it somehow involved Paul Dye ... :D
 
Hose length

5-8% slack in (more or less) straight flexible hoses.
See section 9-30 in AC 43.13-1B.
Dave A.
 
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