Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Sprocket on August 20, 2019, 09:39:41 PM
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Hi - seems I'm spamming the place at the mo, sorry etc...
The gaskets I got with the head gasket set from DS were a bit on the large side, in diameter. When I cleaned the head up I didn't spend a massive amount of time with a dremel on the inside of the tunnel section, so the walls were a bit rough, and I put the poor fit down to that. I put the gaskets in as best I could and fitted the exhaust. I couldn't get the finned collar tight up to the head either, best I could do without feeling like I was going to pull a stud out was to get about 4mm thread showing in front of the nuts (and spring washers). That right? or am I being too soft?
Because the engine was making a ticking noise I suspected a leak on #3 or #4 and no amount of 'just nipping up' was making me feel like it would help, I decided to take the exhaust back off and look. I'm reasonably confident the gasket for #3 was leaking a bit because it wasn't squashed as well as the others.
I've a replacement (not Honda) set now that appear to be a little thicker but the same diameter (39.83mm).
I got the dremel out with the sandpaper barrel and have thoroughly cleaned the insides of the tunnel section for #3 and #4, but these gaskets still don't just butt up to the head. I can press them so far with fingers before they start to want to deform - maybe 8-10mm or so away.
If I put the rounded sides in first, I think I might get them it a little further but I've done some Youtube research and the consensus seems to be you put the flat up against the head. I laughed when I read on here someone said put a dob of grease on to hold them in place - I greased the tunnel section to try to get them to slide in a bit, but they get properly wedged in place!!
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The copper exhaust gaskets should measure 38-39mm. Yours at 39.83 will be a very tight fit. I had the same problem in the distant past, I got a set from Sliver and they measured just a tad under 40mm, like yours by the sounds of it. Anyways, some kind forum member sent me the correct size and hey presto, all sorted. I have since replaced them again after rebuilding the engine and the ones that came in the NE gasket set fitted spot on.
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Ok cool, have measured and ordered something more appropriate, cheers!
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I made such a mess of the exhaust gaskets by trying to force them in I gave up and pulled the mangled things out again, I had trouble fitting the exhaust flanges back too. I currently have no gaskets in as was the case when I got the bike. However this has me wondering if there are gaskets down the hole that are so fused in they are hard to detect? I've been poking around with screw drivers et al but still can't be sure! HELP!
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I made such a mess of the exhaust gaskets by trying to force them in I gave up and pulled the mangled things out again, I had trouble fitting the exhaust flanges back too. I currently have no gaskets in as was the case when I got the bike. However this has me wondering if there are gaskets down the hole that are so fused in they are hard to detect? I've been poking around with screw drivers et al but still can't be sure! HELP!
You may have the original asbestos ones in there still. They are difficult to tell apart from actual metal of the seats and are very, very difficult to remove. I would think that if you are riding the bike and the headers aren't blowing, this could be the case.
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I remember digging the ones out of my head, they were difficult to identify initially. Definitely agree with Julie; if it's running without noticeable leaks, leave it. Next time you have to take the exhausts off, have a look with a dental pick.
When I get home I'll measure the depth of the tunnel properly so you can see how far in it goes, perhaps if you compare measurements you could get a better idea of if there's some in there or not. Perhaps a good photo would help? I sometimes take pics with my phone and zoom in, while I'm sat in front of the bloody thing! :o
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Remembering back to my mechanical engineering days the rule of thumb to work to for thread exposure above a nut should equal the bolt diameter. So, if you have a 6mm exhaust stud there should be 6mm of thread protruding from the nut after tightening. This theory applies to all sizes, so a 8mm bolt will have 8mm of thread showing above the nut etc.
I've always had problems with the exhaust gaskets being a bit big, I normally find a socket of the same diameter as the exhaust port and use it to tap them in and stop the gasket deforming.
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,,,,I've always had problems with the exhaust gaskets being a bit big, I normally find a socket of the same diameter as the exhaust port and use it to tap them in and stop the gasket deforming.
What if you end up with a socket getting stuck in there? :o
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Use the split collets as a drift to seat the gasket in firmly. Usually only needs a couple of taps with a hammer.
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Good idea Mike. When I use a socket I make sure it's slightly smaller than the exhaust port!
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Not sure if this will be helpful or not, but I measured the distance from the lowest side of the front of the tunnel on #4 to the mating face.