Exhaust gasket issues

Yesterday I started reassembly of the top end of my motor. Everything went fairly well, except of course I need a couple of valve shims I don't have (two of them were not measurable after a valve job and the shims I ordered didn't quite bring me into spec).

But, as I was attempting to reinstall exhaust, I ran into an issue. With the new header pipe gaskets, I can't get the headers close enough to the motor to thread nuts onto the exhaust studs. I ordered the top end gasket kit from @chacal so I assume they are the right part, but I suppose it's possible there was a mix-up (in all the hundreds of dollars I've spent with him, this would certainly be the first time!).

I took some measurements of the gaskets, and they are: .221" or 5.61mm. Can anyone confirm this is the right thickness for my XJ650G motor? EDIT: Len confirmed this thickness is correct for the aftermarket gaskets. OEM is approx 3.5mm.

I know I removed the old gaskets from the exhaust ports during disassembly, and while it almost looks like there is still something in the exhaust port, I pried a bit and even tapped a chisel in to see if it was copper or what... and it's definitely looking like aluminum. I looked at some other pictures of exhaust gasket mating surfaces on heads on this forum and mine look the same as everyone else's so pretty sure there's nothing funny going on.

Any ideas?

 

Are you trying to install the whole ehxaust assembly to the head at once?
Each head pipe needs to be installed individually, and in the correct location.
Otherwise I can't see anything in your pics that would be causing the problem.

 

The 3rd pic it looks like the old gasket is still there. They can be difficult to get out sometimes. Try an angled oring pic to try and get behind it and pull out.
You have the right gaskets and they will work.

 

I have the exhaust separated into halves right now - and had tried mounting up one side. I had no issues getting the header pipes up to the exhaust ports and getting the cast aluminum flange started over the studs, but only had 1-2 threads visible and could not get the nuts started. It appears that the gaskets are too thick, and I'm pretty darn sure it's not an issue of angle or anything as the headers are seated flat against the gaskets, and the gaskets are seated flat against the head...

 

See that is what I thought at first, and I looked at this thread: https://www.xjbikes.com/forums/thre...you-have-them-and-how-to-remove-w-pics.29356/

Look at the fourth picture down, I think that is exactly what mine looks like.

Also, as I mentioned, I drove a chisel into the inner side of that metal to see if it would do anything and it didn't move at all, and looked like solid aluminum (not a thin aluminum shell with some other material inside). I'm not 100% certain that it's not a gasket but I'm 95% certain. What I really need is a depth measurement from some common reference point to the gasket seat surface, as that would tell if if that "thing" is part of the head casting, or a spacer/gasket/whatever.

 

Your head looks good, I just compared to pics of my head after blasting. Did you change studs at all?

 

Great, thanks for the confirmation! No, studs are the same as before the rebuild, and were never removed.

 

I would sure like to know the outcome of this.I am about to try and mount mine.I heard they are crush washers, and flatten out as the nuts are tightened down.

 

Just replaced mine ...I thought I had the old gaskets out ...the gasket had split went back and looked closer it was real difficult to get it out it looked like it was part of the head but with a pick it came loose.

 

This is correct.

 

Hmm well I will give it another hard look tonight, and I have a friend coming over who will give me a second opinion on it...

Seems that either "Old gasket is still in there" or "Old gasket doesn't appear to be there" are my only two options (I'm a master of the obvious), but the second doesn't explain why there's not enough clearance to get the exhaust nuts started. I'll let you guys know what I figure out.

Thanks for all the input!

 

In looking at your picture and those shown in Big fitz’s write up, it looks to me that your gaskets are still in there. See if you can find the specs on the delpth of the sidewalls of the exhaust port without the gasket and compare it to yours. Chacal May have that measurement.

 

does look like the gasket is still in there you can see the line where it meets the head

the exhaust nut accepts an allen wrench to tighten it up. nut is not threaded the full length

 

Well I had my friend (who works on large compressors and vacuum pump systems and has plenty of automotive/motorcycle experience) come and double-check - he did the same thing I did, attempted to use a chisel to bite into the "gasket" that was still in the head. No movement, and it was solid aluminum, not a copper/aluminum shell filled with heat-resistant material. He agreed that the ring we are seeing is the head and not a gasket.

We were able to pre-crush the gaskets a little (from 5.6mm to 4.5-4.75mm thickness) between two steel plates in my vise; fit the exhaust, and use a pry bar to apply some force to the "header pipe flange ring thing" to get the nuts started. I had to use two stainless 6mm x 1.0 nuts I had sitting around because I believe we stripped the first couple of threads on 2 of the OEM flange nuts. While we were able to get the exhaust installed and it should be OK for now, I don't like this solution long-term, and I'll be ordering replacement nuts and some thinner gaskets.

I don't really know what gives; on a stock motor with stock exhaust this really shouldn't be a problem. All I can think is that the aftermarket gaskets are too thick; but why would they be sold? I can't be the first person to run into this problem. So that leads me back to the "gasket" in the head that looks like solid aluminum. Perhaps the PO had some spacers made up of solid aluminum and they were a very tight fit? I tried to probe the center of the ID of the ring with a heavy-duty pick and it did not go through; the only thing that makes sense to me is that it's solid metal and not a gasket.

If anyone has a 1980 head sitting around and can take some measurements for me, I'd love to solve this mystery. PM me and we can work out a common reference point to measure from. I'm thinking from a straight edge placed across the exhaust studs down to the exhaust gasket mating surface.

Thanks!

 

I have an 82 head out ibn my shed.I will measure.Not sure exactly what you mean.Lay a straightedge across one of the studs protruding from the head, one the exhaust flange would go over, and from there the distance to the opening of the exhaust opening? Or from the outer surface of the exhaust hole to the bottom of the opening, which looks like 1/4 inch or so? I dont have a metric ruler, but can give either measurement in inches.

 

I cant find any measuring device.But it is easy to see the crush rings are still in there. it is barely more than a 1/4 inch deep with the washers/gaskets still in there.

 

Yeah basically put a straight edge of some sort across the top of the studs and measure from the bottom of that down to the port opening, where the gasket would sit (assuming yours doesn't have gaskets installed). That would give us a very close measurement to know whether there are gaskets installed, as the gaskets are about 1/8" thick for OEM and just under 1/4" for aftermarket that Len sells.

 

XJ750 head, which I suspect is the same

Head surface to bottom 8.5mm - gasket is removed
Stud length from boss on head 31.8mm
Top of stud to bottom of gasket mating surface 48mm

 

This head I am working on has the gaskets in place and have not been removed yet.
First pic is 14 mm to gasket
Second pic is 7mm to gasket
So you still have gaskets in place and there is no lip on exhaust port as shown in you picture

 

Just a thought but it is possible the exhaust studs may have been replaced at some point with shorter studs?

 

tomanybikes measured from points on the head ,but yes you should not measure from end of stud

 

in the original picture, on the bottom of the port, there's grind marks. but not on the next ring. clue

 

you have to use that there arithmetic stuff

 

I keep forgetting to post back here, but I ordered the Yamaha OEM exhaust gaskets from Len (instead of the aftermarket ones that came with my gasket kit), and the exhaust bolted up just fine. So maybe on my setup there was just less tolerance for thicker gaskets.