Topic: HM300 vs HM341 Exhausts

[caluser2000]

I was always told short rides in cold weather cause condensation.  Your mileage may vary.

It does. After a while the drain holes at the bottem of the mufflers get clogged and if not clear rot the mufflers from the inside. Are where there are sulfur (like volcanoes, natural steam pools and the like) and a lot of salt on the air it is worse.

[stayathomedadwithnokids]

New member here, 2nd owner since 1994: '71 CB750 K1
thought I'd pass on my purchase experience buying mint condition new old stock HM300 pipes, still sealed in plastic bags in Honda boxes.

6/9/13.  26,357 miles
Purchased new mint condition OEM 4-into-4 HM300 exhaust system for $2694.70 from JTMARKS.   Perfectly sealed in original wrapping/protection/and boxes.  Sold old 1972 HM341 exhaust system good but not perfect condition on eBay for $850, fyi.  Bought those 4 HM341 in 3/1994 from Fremont Cycle Salvage for $200..to replace the Sanderson drag pipes that came on the bike from the original owner.

Thought I'd share some pricing perspective.  100% happy with the HM300's on my K1.

[caluser2000]

New member here, 2nd owner since 1994: '71 CB750 K1
thought I'd pass on my purchase experience buying mint condition new old stock HM300 pipes, still sealed in plastic bags in Honda boxes.

6/9/13.  26,357 miles
Purchased new mint condition OEM 4-into-4 HM300 exhaust system for $2694.70 from JTMARKS.   Perfectly sealed in original wrapping/protection/and boxes.  Sold old 1972 HM341 exhaust system good but not perfect condition on eBay for $850, fyi.  Bought those 4 HM341 in 3/1994 from Fremont Cycle Salvage for $200..to replace the Sanderson drag pipes that came on the bike from the original owner.

Thought I'd share some pricing perspective.  100% happy with the HM300's on my K1.

Looking good.

Welcome to the Honda SOHC forums stayathomedadwithnokids.

[grcamna2]

New member here, 2nd owner since 1994: '71 CB750 K1
thought I'd pass on my purchase experience buying mint condition new old stock HM300 pipes, still sealed in plastic bags in Honda boxes.

6/9/13.  26,357 miles
Purchased new mint condition OEM 4-into-4 HM300 exhaust system for $2694.70 from JTMARKS.   Perfectly sealed in original wrapping/protection/and boxes.  Sold old 1972 HM341 exhaust system good but not perfect condition on eBay for $850, fyi.  Bought those 4 HM341 in 3/1994 from Fremont Cycle Salvage for $200..to replace the Sanderson drag pipes that came on the bike from the original owner.

Thought I'd share some pricing perspective.  100% happy with the HM300's on my K1.

Looking good.

Welcome to the Honda SOHC forums stayathomedadwithnokids.

Welcome

[Don R]

My 500 exhaust rotted out in 2 seasons but I rode in the cold on short trips.  Any new exhaust I get now gets coated on the inside and baked to cure it before it's ever installed.

What do you coat it with Don R?

This, https://www.eastwood.com/eastwood-hi-temp-internal-exhaust-coating-w-nozzle.html

 When you look inside to see if it's covered you spill silver paint on your shoes. Plenty of paint. Now I tape the ends and clean out the drain holes when done. New pipes only, I don't think it would stick in used ones.

[caluser2000]

My 500 exhaust rotted out in 2 seasons but I rode in the cold on short trips.  Any new exhaust I get now gets coated on the inside and baked to cure it before it's ever installed.

What do you coat it with Don R?

This, https://www.eastwood.com/eastwood-hi-temp-internal-exhaust-coating-w-nozzle.html

When you look inside to see if it's covered you spill silver paint on your shoes. Plenty of paint. Now I tape the ends and clean out the drain holes when done. New pipes only, I don't think it would stick in used ones.

Yeah cleaning out used pipes would be a huge pain in the rectum. And right messy as well. Putting fish oil from new was a thing back in the olden days to extend steel made muffler life. Some folk used deisol to coat them as well.

[BenelliSEI]

Regarding the drain holes (in the mufflers, bottom, right where they join the head pipe):
On all of my older, still in nice shape, pipes I use a sharp 1/8” drill to keep them clear. I suspect that when new these holes only went through the outer shell (the muffler overlaps the thick wall head pipe at this junction).. I’m not shy. I drill right through everything. Each Fall I make sure I poke up through the hole and keep them clear. Give every pipe a good shot of WD40 (using the straw, in the hole and down the baffle). Seems to help.

I also never use the old bikes/pipes for short rides. If it gets used, it’s a decent length ride, with lots of twist. Blow out the crap, and get them hot!

[KasperK/Denmark]

Nothing rots an exhaust more and quicker than short trips. The exhausts rot up from the inside due to condensation. Long trips and long stretches heatens up the pipes and prevents condense.

[PeWe]

Living close to salt sea will help the rust too?
Some guys here lives where the climate is very humid.

I remember how much more humid it was in South Carolina (Greenville/Spartanburg) end of October, beginning of November when I was there for 2 weeks 2001.
This compared to central Sweden 100km west of Stockholm.

I suppose that Denmark gets humid air from Northern Sea.

[caluser2000]

Living close to salt sea will help the rust too?
Some guys here lives where the climate is very humid.

I remember how much more humid it was in South Carolina (Greenville/Spartanburg) end of October, beginning of November when I was there for 2 weeks 2001.
This compared to central Sweden 100km west of Stockholm.

I suppose that Denmark gets humid air from Northern Sea.

Yes salt does speed up corrosion. Some cuontries use salt on their roads during when ice gets formed on the road.

[ekpent]

Mouse piss is the worst !! Plug those holes when in storage. Always fun to see what shoots out exhaust pipes,especially 4 to 1's when you start up old dormant project bikes for the first time.