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Old 10-26-2009, 03:09 PM   post #1 of 4
htm-ply
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Join Date: Oct 2009
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Help Honda GX340 Exhaust

Have 2 Honda powered air compressors (GX340's) that both now have the same problem.....stock exhaust manifold keeps coming loose, to the point of sometimes falling off before I can shut it down! Have drilled and heli-coiled both, now to no avail. Everyone here seems to be really knowledgeable, hopefully someone has seen this before or can help me solve this problem. I'll also ask if there is a "quieter" exhaust available other than stock. These compressors run 20-30 hours a weekend, and it sure would be nice to quiet them up a bit
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Old 10-26-2009, 07:27 PM   post #2 of 4
larryccf
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Default Re: Honda GX340 Exhaust

not sure how the exhauest flange is attached to the cylinder - if there are studs, you might try putting a jam nut over top the original nut, screwing it down, then tightening one against the other
if the stud isn't long enough, then replace with a stud that is - if bolts are employed, then replace with a stud - www.mcmaster.com is a good source for anything, including studs -

as to quieter exhaust, instead of fooling with mounting a different exhaust system, you might try doing what i did on my generator with a really really loud 20hp honda engine

as long as you make sure the diameter of the pipe leaving the orig muffler is large enough to not impede flow, all you'll be doing is decreasing sound - and keep in mind, the large the volume of the muffler, the quieter it'll be

the set up in the below pix took me from an ear pounding headache that even my neighbors complained about (and we've got huge yards) to a noise level you can't hear inside the house and standing 10 feet away you can hold a normal volume level conversaion with no need to shout to be heard

for my use, as i had already built the shed, i used a quick detach clamp (really a sanitary clamp from the food industry, but it's 316 stainless and would take the heat) - you can see it hanging off the muffler in the first shot

in the second shot, you can see the stainless flex exhaust line - it just slips into the muffler - it's 2" OD and the muffler ID is 2.5" so it's not even a tight fit but it slides in about 8"



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Old 10-26-2009, 07:55 PM   post #3 of 4
rscurtis
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Default Re: Honda GX340 Exhaust

If you're losing mufflers on that engine, it is most likely that they are being overloaded. I have seen this happen on Little Wonder leaf blowers, which work the engine very hard. If you cannot get two good studs in the head, then head replacement is the next option. The solution is to reduce the engine speed so the throttle is not wide open when it is under load. Note that an engine's horsepower is an intermittent rating, and that continuous ouptut should be somewhat less.
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Old 10-26-2009, 11:51 PM   post #4 of 4
TCam
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Default Re: Honda GX340 Exhaust

Hi htm-ply,

If you would like a quieter muffler set up, Larry's method works well and is way less $$ than Honda's quiet generator muffler set up for $400!

Loose mufflers are covered in Honda service bulletin OHV Engine #16. I tried to attach the reduced size serv bulletin pdf (325 kb) and it is still too large to attach. I donít know how to reduce the 4 pages to meet the 205 kb maximum on this site. Send me an e-mail: ftcam at yahoo.com and I'll forward it to you.

The service bulletin lists the new part numbers for hardened studs and a stainless steel laminate exhaust gasket instead of the graphite gasket. We saved several cyl heads by tapping the head 3/8" instead of the standard 8mm and installing grade 5 bolts through the exhaust manifold it worked fine.

The Honda muffler design works okay if the vibration level is normal (less than 7 G to meet Honda's standards) but if it is higher then the studs loosen and break. We see this problem in our shop on belt driven units, rarely on direct drive application. We use an accelerometer to measure the vibration to see if it is in allowable limits but you can tell just by putting your hand on the fuel tank if it is really starting to buzz.
If everything isn't just right such belt tension, belt condition, belt alignment and engine rpm (3400 to 3600) the studs will loosen and break. The engine rpm is important because a difference of 100 or 200 rpm, lower or higher, can completely change the harmonics and resonance. Try different rpm settings. Hope you can save that head! TC

For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. John 3:16
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