Topic: CB750 K3 Mac 4-2 Megaphones... Anyone have problems with fitment?

[paulages]

I'm working on a customer's bike that is something of a restoration/ customization project. Apparently he had a pretty nice CB750 in the early '70's and the wife made him sell it when the kids came along... now he wants another, and we're trying to recreated it as close to the pictures he has as possible. Just about everything has been replaced with upgraded or NOS parts. I installed a Webcam 41A camshaft while the engine was out, but the engine is otherwise stock.

Anyway, the details aren't really relevant to the question, but I know you guys like your stories and eye candy.   He really wanted a Jardine 4-2 exhaust, but we settled on a Mac 4-2 until he finds a suitable replacement, preferably a stock HM300 system. The problem I'm having is the fitment of the headers to the exhaust spigots... the exhaust clamps tighten well to the head pipes, but they don't clamp onto the spigots. It seems like the reliefs cut into the pipes that allow it to tighten against the spigots aren't long enough to do the job. When the exhaust collars are tightened all the way down, the pipes can still pull away from the head.

Has anyone else had this problem with Mac pipes? I never have with 4-1's...

[72 yellow]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

[paulages]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

[72 yellow]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

Just curious, I have a 71 Lightning w/export tank and a couple of other mods.

[paulages]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

Just curious, I have a 71 Lightning w/export tank and a couple of other mods.

I hope one of those mods is an SRM oil pump?

[72 yellow]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

Just curious, I have a 71 Lightning w/export tank and a couple of other mods.

I hope one of those mods is an SRM oil pump?

Not yet.  Still runs pretty good.  No unusual noises.  Oil light flickers at idle only.

[paulages]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

Just curious, I have a 71 Lightning w/export tank and a couple of other mods.

I hope one of those mods is an SRM oil pump?

Not yet.  Still runs pretty good.  No unusual noises.  Oil light flickers at idle only.

Watch out! That pump is the Achilles heel of that engine!

[72 yellow]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

Just curious, I have a 71 Lightning w/export tank and a couple of other mods.

I hope one of those mods is an SRM oil pump?

Not yet.  Still runs pretty good.  No unusual noises.  Oil light flickers at idle only.

Watch out! That pump is the Achilles heel of that engine!

Hmm..Thought the cast iron ones were better...

[paulages]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

Just curious, I have a 71 Lightning w/export tank and a couple of other mods.

I hope one of those mods is an SRM oil pump?

Not yet.  Still runs pretty good.  No unusual noises.  Oil light flickers at idle only.

Watch out! That pump is the Achilles heel of that engine!

Hmm..Thought the cast iron ones were better...

They are, but still often leak at the end plate, half joint, or mating surface to the case, causing oil pressure loss before the oil even gets anywhere. Lots of people seem fine with the flickering oil light at idle, but it never made me comfortable. One engine I rebuilt top to bottom with all new bearings and bushings ended up seizing because of a faulty oil pump... the irony is that the guy had bought an SRM pump at my advice and just hadn't installed it yet.

ANYWAY... noone's had this problem with the MAC pipes?

[72 yellow]

Can't help with your question, but is that a Rocket 3 in the bottom photo ? 

Yes, a '71. Can't wait for it to leave the shop... 

Just curious, I have a 71 Lightning w/export tank and a couple of other mods.

I hope one of those mods is an SRM oil pump?

Not yet.  Still runs pretty good.  No unusual noises.  Oil light flickers at idle only.

Watch out! That pump is the Achilles heel of that engine!

Hmm..Thought the cast iron ones were better...

They are, but still often leak at the end plate, half joint, or mating surface to the case, causing oil pressure loss before the oil even gets anywhere. Lots of people seem fine with the flickering oil light at idle, but it never made me comfortable. One engine I rebuilt top to bottom with all new bearings and bushings ended up seizing because of a faulty oil pump... the irony is that the guy had bought an SRM pump at my advice and just hadn't installed it yet.

ANYWAY... noone's had this problem with the MAC pipes?

Didn't mean to hijack..Thanks for the info..Bike came out of your neck of the woods.  Bend, OR.  Was supposed to be one of the bikes from the Sandy bandits shop.  Thanksagain.

[paulages]

Eh, I hijacked it as much as you did... not worried about it, I just want someone to chime in on the exhaust. Calling Mac now anyway.

Just about everything around here supposedly came out of the Sandy Bandit's collection... 

[paulages]

Problem solved... The exhaust system was supposed to come with Mac clamps and didn't. It's a shame, because we order NOS Honda clamps. He'll be upgrading to a stock system at some point anyway, so it's not a total loss.

Thanks for your help, paulages! 

Paul

P.S. 72 Yellow, we can go back to talking about BSAs now. 

[72 yellow]

Problem solved... The exhaust system was supposed to come with Mac clamps and didn't. It's a shame, because we order NOS Honda clamps. He'll be upgrading to a stock system at some point anyway, so it's not a total loss.

Thanks for your help, paulages! 

Paul

P.S. 72 Yellow, we can go back to talking about BSAs now. 

   

[paulages]

I'm reviving this thread because there does seem to be a problem with the Mac pipes themselves, and I'm afraid this could become a "bad seller" review...

It appears to me that the reliefs cut into the end of the headers that allow the exhaust clamps to... well, clamp the headers to the spigots, aren't long enough. They are about 3/8" shorter than the stock pipes. I've been back and forth with a tech guy at Mac, and I'm currently supposed to send the pipes back for them to examine. We'll see how this pans out, but I'm a little frustrated to have to shell out shipping out of pocket for what appears to be a defective product.

Anyway, I'll keep you guys informed as to how Mac handles this.

[72 yellow]

I'm reviving this thread because there does seem to be a problem with the Mac pipes themselves, and I'm afraid this could become a "bad seller" review...

It appears to me that the reliefs cut into the end of the headers that allow the exhaust clamps to... well, clamp the headers to the spigots, aren't long enough. They are about 3/8" shorter than the stock pipes. I've been back and forth with a tech guy at Mac, and I'm currently supposed to send the pipes back for them to examine. We'll see how this pans out, but I'm a little frustrated to have to shell out shipping out of pocket for what appears to be a defective product.

Anyway, I'll keep you guys informed as to how Mac handles this.

And I won't ask anymore BSA questions.