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YOSHIMURA 4-1 Help

  • Thread starter Thread starter maro
  • Start date Start date
I punched 20 of the holes out to 1/4". No noticeable noise increase. I also replaced the rear progresso can with a steel electrical baffle for a 3 inch round junction box. It was an immaculate fit in the rear of the pipe, took a little tap to seat, no rattle. I secured it with three pop rivets, I will add a fourth for security. I'm heading to Lowes to get SKU numbers and local prices for this, I've gotten a few requests from people that want to know how it's made.

Sure cheaper than used baffles on Ebay.
 
Bump

Duane,

I went to Lowe's today and bought the parts based on what I see in the photos

I also bought a 3/4" floor flange because it seemed closer to the header ID

So, I found

Header ID - 3.38"

1" flange OD - 3.76"

3/4" flange OD - 3.42"

3 1/2" round ceiling box OD - 3.35"

So, did you grind .4" off the 1" flange to fit it at the back?

I don't want to drop to the 3/4" nipple as the volume decreases 45%
 
Last edited:
Big T said:
Bump

Duane,

I went to Lowe's today and bought the parts based on what I see in the photos

I also bought a 3/4" floor flange because it seemed closer to the header ID

So, I found

Header ID - 3.38"

1" flange OD - 3.76"

3/4" flange OD - 3.42"

3 1/2" round ceiling box OD - 3.35"

So, did you grind .4" off the 1" flange to fit it at the back?

I don't want to drop to the 3/4" nipple as the volume decreases 45%
Click to expand...

I had an additional 1 inch worth of threads added to one end of the pipe for it to fit. lowes threaded it some more for free.

I started grinding the flange down and test fitted it as it got close. When the flange went deep enough for all 12 inches of pipe to fit with 1/4" showing out the back It was done. Then I drilled the intake holes on the ground flange. This is critical since you want a tight fit that won;t rattle yet you don't want to force the flange in adn damage the pipe.

The electrical box was a ceiling fan mount plate, it was a perfect fit and had 1/2 of material to attach to the pipe with pop rivets.
 
So you're talking about the inner flange?

What about the rear one?

THe ID shown is at the rear of my pipe, so both 1" flanges are too big?
 
That's the beauty. The rear flange fits right over the back with a small lip, maybe 1/8" all around. The electrical box has two holes that line up perfectly with the flange, allowing the other two to be marked and drilled precisely. The electrical flange needs to have a 2 inch hole cut in the center, I used a jig saw with a scrollable metal blade to carve it out.
Alternatively you could cut the rear baffle a bit to fit inside the pipe but we liked the look it had. And it is easy to remove.

The pipe and forward baffle is inserted into the pipe snug. The rear is threaded on until it comes to rest against the muffler. The pipe should be flush with the rear of the flange if about 1/4" of pipe is protruding.

I leveled the 4 screws with the ground for appearance and then drilled a few holes for rivets to hold it. I used stainless steel M6x20mm bolts and nuts for the hardware to attach the flange to the electrical box, didn't want rust lines down the back. Use aluminum or stainless steel rivets if possible.

I packed it with a single bale of #3 steel wool loosely spread around the pipe. It seems to be holding up well. It doesn't catch fire or blow out the back.
 
Found this on Ebay; contact sellerr for a "reproduction" Deffuser pipe

http://cgi.ebay.com/ebaymotors/HOND...7471173QQptZMotorcyclesQ5fPartsQ5fAccessories

HONDA CB750 K0-K7 F1F2 EXHAUST BLACK YOSHIMURA TYPE NEW M012with a Diffuser Pipe and six Bolts.6mm hexagon wrench is required.
Yoshimura of those days had many kinds of exhausts.
The type bent by the hand of the first stage in it was reproduced faithfully.
In addition, deffuser pipe is different.
Old Yoshimura type deffuser pipe is 5250JPY separately.
 
Maro, that sounds like a reasonable alternative assuming your pipe is in good shape. Exhausts can be a baich especially if you are hooked on Yoshi :D

stuff is out there. recent find NOS pipe for CBR600 but can is identical to my ED

picture.php
 
Actually, I gotta say, the baffle Duane put together is pretty sweet and really quiet. Plus I can continue to play with it for better flow if need be. For less than 20 bucks, I'm extremely happy. I was over at Duane's garage last night and we pulled it out and sliced some more notches into the flange that meets the mid-pipe to help the flow even more. I should have taken a photo of it:(. I will take an updated shot of it ON the bike this weekend. Looks great!

It's nice to see however that the possibility of acquiring a yosh baffle that would fit this old pipe is achievable.

FYI, We also studded the head block where the header bolts on. This was done as I have to take the whole header off in order to change the oil (which I did as well last night). There is always that fear of stripping those aluminum threads inside the header. Now that we studded it, I can just screw some bolts on and off the studs (like the oil filter cover). I will say this though, getting that 4-1 on and off is a PITA. I can't imagine doing it alone.
 
I have been using SS bolts with plenty of anti-seize. What was your source for studs? The last supplier I spoke to said I would have to cut them out of all thread stock.

My Ysohi comes down the center as well, but there is a mid pipe which allows the can and mid to be removed with one bolt. The header is a bit of a pita, and studs would be a little easier and probably much safer in the aluminum head.
 
I did a bit of a variation on Duanedge's set up, with a reducer and a 1/2" flange in the front and skipped the 1" flange in the back, substituting a bolt, a big washer and using the ceiling fan mount. I think the ID of my can is somewhat smaller than Maro's, I had to pound the fan mount into place.

It still seems kinda loud, but nothing like the open pipe

I may pack more steel wool in there.

I've got 68 1/4" holes in the nipple
 
The replacement baffle maro posted about is too small, about 2.75 inches, for the Yosh pipe he has. It runs about 3.25.

The muffler on Maro's bike was so quiet I did not even hear it go past me on the road. So we can punch a little more out without getting tickets. It's fun to pull the baffle and modify it, we have the option of starting over if we go too far with another 7 dollar part.
 
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