Topic: Well F*&% IT, I guess Ill have to use two (LEAK POTENTIALLY SOLVED)

[VTCBike750]

So Im not too sure why my #1 exhaust keeps leaking.
Its a 72 750 with a kerker 4-1.


#1 had a small leak so I put in new ones

New one started leaking, took it apart, everything looked assembled right.  Reassembled it while waiting for new ones to come in the mail, but the exhaust header #1 was loose  . WTF.

Swapped them all out for brand new ones, made sure the ports and flanges were clean (with acetone), no oil or anything and all seemed gravy.

Until today, warming up the bike and POP! #1 Exhaust is leaking AGAIN, not to mention the header to #1 is loose.

I GUESS ILL JUST HAVE TO USE 2 GASKETS THERE?

It doesnt seem like Id have to, but???

[KingCustomCycles.com]

Tweaked in a crash?  PO pulled real hard on it to "improve" the fit?  Spacers too short or studs too long?  Rear mount not properly located or angled and is applying pressure?  Thats all I got in 30 seconds.

[VTCBike750]

Tweaked in a crash?  PO pulled real hard on it to "improve" the fit?  Spacers too short or studs too long?  Rear mount not properly located or angled and is applying pressure?  Thats all I got in 30 seconds.

Well it was wrecked before I got it. So who knows? The rear mount's angle may be a problem.


Is using 2 gaskets a bad idea? Ive heard of people finding 2 in there.

[KingCustomCycles.com]

I have pulled as many as three out.  Try to figure out what the misalignment is, if that fails, or it is something you can't do anyting about, two will be fine. 

[VTCBike750]

Yup looks like Ill be putting in 2.

[VTCBike750]

Yeah, I really have no idea why it loosens up. Its like the spacers in that one exhaust are too short, but the same length as all the rest.

[KRONUS0100]

if thats a pic of the bike , you better look close at exhaust header.that is an F model collector, not a kerker.  muffler end cap might be kerker, but that collector is all F model.

[madmtnmotors]

It looks like you are using bolts instead of studs w/nuts? If so, I'll bet your bolts are bottoming out. Take an 1/8" off those bolts and chase the threads clean inside the head (bottoming tap recommended).

[VTCBike750]

Hmmm, does having an F model collector have anything to do with the leak?
I dont think the rear mount is effecting anything, nor the angle.

Yeah bolts arent bottoming out. At first its great, then after some riding it loosens up?

Right now Ive stuck 2 gaskets in there, but would love to figure out whats going on.

[madmtnmotors]

Studs with nuts might work better. As the bolts are tightened they are exerting both twisting and pulling forces on the aluminum threads inside the the head. When studs are used the twisting force is more concentrated between just the stud and the nut (both steel) while the stud remains stationary (hopefully) in the aluminum head and forces between the two are almost completely limited to pulling force only. I would be afraid of eventually stripping the holes in the head by using bolts. Switching to studs with nuts would also seem to be a very cost effective experiment (inexpensive) and you can always switch back to the bolts if you don't like the studs/nuts.

[VTCBike750]

Its interesting that you brought this up. The PO had partly stripped some of the bolt holes. Particularly #4 and 3 and well today I got to helicoil #4. Need to helicoil one of #3's in the near future.

The thing is, I can tighten down the bolts on #1 until the metal flange is flush with the head and after 100-200 miles its loosened up? The bolts don't loosen and the flange is still flush with the head.  Its the exhaust header that's loose within, as though there isnt a crush washer in there.

[WarwickE36]

Do you still have lock washers in between the bolt head and flange?

My old RX7 turbo/downpipe bolts used to loosen up every 500 miles or so, even with lock washers, but there was A LOT of heat going through that turbo.

[VTCBike750]

Nope, bolts arent loose.

[VTCBike750]

Is there any type of sealant I could use?

[VTCBike750]

Studs with nuts might work better. As the bolts are tightened they are exerting both twisting and pulling forces on the aluminum threads inside the the head. When studs are used the twisting force is more concentrated between just the stud and the nut (both steel) while the stud remains stationary (hopefully) in the aluminum head and forces between the two are almost completely limited to pulling force only. I would be afraid of eventually stripping the holes in the head by using bolts. Switching to studs with nuts would also seem to be a very cost effective experiment (inexpensive) and you can always switch back to the bolts if you don't like the studs/nuts.

Experiment underway.  Studs purchased from local dealer for a grand total of 9 bucks.  Ill probably Helicoil some of the other holes that are questionable. 

Let you guys know.

[madmtnmotors]

The thing is, I can tighten down the bolts on #1 until the metal flange is flush with the head and after 100-200 miles its loosened up? The bolts don't loosen and the flange is still flush with the head.

Sounds like the spacers are to short (overtorqued too many times?) or they are installed backwards. The raw edge goes towards the head, while the rolled edge goes to the outside and fits inside the clamping collar. The clamping collar should not bottom out on the head. I made the mistake of installing the spacers backwards once but I don't remember what or why I was compelled to correct the issue. I have owned my 750 K8 for 25 years and I made this mistake way back in the early years. I do remember the reason I installed them backwards was because it seemed logical to me to install them that way. It was counter-intuitive to me at the time to put the rolled edge to the outside, but that's how they have to be to work correctly.

[VTCBike750]

Yup, installed the right way and the spacers are the same size as all the rest.

The only thing I can think of is the header on #1 has a vibration when the bikes running and this vibration some how causes the copper gasket to get compressed further.

It will go from being assembled fully, everything nice and tight. Then a POP and the exhaust rattles in the head even with everything tightened down. Im gonna check the band that clamps the pipe to the collector

Other than that IDK

[chickenman_26]

Hmmm, does having an F model collector have anything to do with the leak?

Just a thought.... The pre- '77 750K had a different exhaust mounting arrangement than the F, with a flange bolting to the head to crush the exhaust gasket and the pipe clamped to the flange. The K and F cylinder head part numbers are different, so it's possible the split collar arrangement won't work on the pre-'77 k models. Maybe the split collars aren't deep enough to work on the earlier heads.

Stu

[madmtnmotors]

Maybe the split collars aren't deep enough to work on the earlier heads.

Stu

Stu might be on to something. I don't think the heads are different (but they COULD be), although I have done a side-by-side visual comparison of a loose spigot from a pre 77' 750 next to a loose split collars/clamping collar from a post 76' 750 and there's not a lot of margin for error, Looks like a thinner flange on the headpipe could make a difference. I'm swamped here this evening but I can probably take some critical measurements and post some picts tomorrow. You may very well have to stack two crush gaskets at the offending port. Two new gaskets might seal better than a new gasket over an ABC (already been crushed) gasket.

[VTCBike750]

I would greatly appreciate it madmtn.  Im pulling out my hair on this one.

You guys think that these exhaust gaskets could be better to use?

[madmtnmotors]

Okay, took a little longer than expected to get the comparison pictures but here they are. On the left is the late model split collar with clamping collar, while on the right is the earlier model spigot. The late model is a shorter assembly but is designed to include the thickness of the flange on the end of the head pipe. Pictures titled "Offset 2" and "Offset 4" show the late model split collar with an approx .215" plywood shim.

The dimensions referenced in picture "Collars 2A" that represent the working height of each from the underside of the flange to the bottom of the assembly.

The "XX" dimension for the late model split collar is: .885 in

and the "YY" dimension of the spigot is: 1.025 in

for a difference of .140 in. So if the header flange is less than .140 in then there may not be enough compression on the gasket to hold a good seal. If this were the case then a thicker gasket would be in order.

[754]

If you have a bad header, or a bend in #1 pipem, that should not be there, it will always give you trouble..
 If all are tight, loosen the bad one and see how far it moves before it stops.. if its more than 1/8 inch, there is your problem..
 Any burrs on the header flange or flat spot..where it meets the gasket ? ?
 might have been dropped..

[VTCBike750]

Madmtnmotors, Excellent. Thank you so much.  I wonder if anyone has ever made this comparison.

Im down stairs in the process of helicoiling some exhaust holes that have seen better days, installing studs instead of bolts, and about to mount the exhaust. I only have new copper gaskets right now, but have the thicker steel fibre ones coming in the mail.  If the copper ones give me anymore trouble then Ill just swap them out.  Ill let you know the thickness of the F models header flange. Ill also measure the depths to the exhaust ports too.

[VTCBike750]

If all are tight, loosen the bad one and see how far it moves before it stops.. if its more than 1/8 inch, there is your problem..
 

Ill take a look at this too.

No burs or visible bends.  How would I be able to see if the header is bad?

[VTCBike750]

So the exhaust is back in action. I dont know if it is leaking since #1-4 wont fire, but thats a whole other issue.

I did find out that the exhaust flange is 2.8 mm thick. Which comes out to 0.1102" So a thicker gasket could be a solution. 

BUT...I did find out per the suggestion of 754 that #1 does have a little movement. Further inspection reveals a very small little lip in the exhaust port.  I believe that the exhaust was getting hung up on the lip and as the bike ran the exhaust would get loose.  This time I lifted the exhaust and bolted it down onto my studs. 

Temporarily problem solved, thanks guys.

Now Im going to go loose my #$%* since Im only running on 2 cylinders  . Yesterday it was fine.  Anyone wanna buy a bike (jk)