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Gun Gum (edit: not JB Weld) around cylinder head (exhaust)

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Bhud
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PostPosted: 16:17 - 03 Apr 2020    Post subject: Gun Gum (edit: not JB Weld) around cylinder head (exhaust) Reply with quote
https://i.ibb.co/YN94QNY/cbf-headers.jpg

More just for curiosity's sake, any idea why someone would do this, and would you bother fixing it (would need a new cylinder head and possibly exhaust system) or is it safe to assume it was just owned by a complete chimp and is probably full of similar secrets so best left alone?

What you're looking at is the exhaust side of a CBF500 (mid 2000s) cylinder head. JB Weld appears to have been lavishly smeared all around the exhaust outlets, and to have made removal of the exhaust impossible as it covers up exhaust header bolts on both sides. There is a huge amount of the stuff. Never seen anything like it before. As you can see, it's even in between the exhaust pipes and outlets.

The bike as a whole runs and works well - although the cooling system will need looking at and a few bits and pieces renewing. What it looks like to me is, someone tried to maintain the bike as best they could, but when the exhaust needed work, they couldn't get it off as the header bolts are covered in JB Weld.

Last edited by Bhud on 17:26 - 04 Apr 2020; edited 1 time in total
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stinkwheel
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PostPosted: 17:37 - 03 Apr 2020    Post subject: Reply with quote
Acetone will soften a lot of epoxies enough for them to peel off when heat is applied.
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Bhud
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PostPosted: 18:16 - 03 Apr 2020    Post subject: Reply with quote
Cheers for the info, but if I mess with it that would make it mine, in this case. And who knows what horrors lurk beneath.
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stinkwheel
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PostPosted: 18:50 - 03 Apr 2020    Post subject: Reply with quote
I wonder if it's actually JB weld though.

The stuff is pretty robust but is it header temperature tough?

I wonder if it's gun gum.
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Bhud
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PostPosted: 18:57 - 03 Apr 2020    Post subject: Reply with quote
Gun gum? Wow, then, if so, it could have been done recently. I hate the stuff - it always crumbles. Could be metal epoxy too. Either way, as the radiator has to come off to get access, there would probably be a good reason for it (i.e. a seriously f***ed head).

Then again, I could be overestimating someone who simply couldn't understand he needed exhaust gaskets, so he plastered it with this stuff. What's really interesting is, it's on both headers, not just one.
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Riejufixing
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PostPosted: 19:11 - 03 Apr 2020    Post subject: Reply with quote
stinkwheel wrote:
I wonder if it's actually JB weld though.

The stuff is pretty robust but is it header temperature tough?

I wonder if it's gun gum.

I'll go with something like that too. JB weld isn't going to stay on the pipes, it will vaporise. It might be that someone sloshed on gun gum to get over some sort of leak for an MOT, perhaps.
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Bhud
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PostPosted: 19:23 - 03 Apr 2020    Post subject: Reply with quote
Riejufixing wrote:
I'll go with something like that too. JB weld isn't going to stay on the pipes, it will vaporise. It might be that someone sloshed on gun gum to get over some sort of leak for an MOT, perhaps.


Now that is interesting. It has a very recent MOT (last Friday). So it could well be that, especially since the stuff hasn't yet crumbled away as Gun Gum usually does. I suppose the best test for this would be to let it sit idling until it gets hot, then tap at it with a long screwdriver to see if it lifts off.

If that's all it is, then I'll be well pleased with that.
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steve the grease
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PostPosted: 19:28 - 03 Apr 2020    Post subject: Reply with quote
surely JB weld would soften at exhaust temperatures?

There are a number of exhaust assembly pastes used in the trade. Gun Gum is a Halfordsy sort of DIY MOT bodge.
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Bhud
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PostPosted: 19:38 - 03 Apr 2020    Post subject: Reply with quote
steve the grease wrote:
surely JB weld would soften at exhaust temperatures?


You're right. Just Googled it and it says JB Weld can withstand up to 316-deg C, while a bike exhaust can get up to 800-deg C.

Quote:
There are a number of exhaust assembly pastes used in the trade. Gun Gum is a Halfordsy sort of DIY MOT bodge.


Sounds promising. If it's just Gun Gum, then it can be chipped off, and it can get new exhaust gaskets (and probably collets too).

After looking at it for a while, I guessed that someone had tried to remove the old exhaust studs, found they were rusted in, and failed to get them out. After various attempts they got them out but damaged the head (and probably the studs), and then got around this by stuffing the cracks and enlarged holes with copious amounts of some kind of epoxy, then stuck the studs back in and simply waited for the stuff to set.
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ThatDippyTwat
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PostPosted: 20:31 - 03 Apr 2020    Post subject: Reply with quote
It's probably Fireclay - I used it a lot on the rat for this exact purpose. I also work in a Foundry with unlimited access to this. It'll crumble and flake like Gungum (which is a thinner refactory cement), but it'll take longer. Best results are to wrap the fuck out of a setup like this, and try to hold the clay where it set.
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Bhud
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PostPosted: 20:43 - 03 Apr 2020    Post subject: Reply with quote
ThatDippyTwat wrote:
It's probably Fireclay - I used it a lot on the rat for this exact purpose. I also work in a Foundry with unlimited access to this. It'll crumble and flake like Gungum (which is a thinner refactory cement), but it'll take longer. Best results are to wrap the fuck out of a setup like this, and try to hold the clay where it set.


Interesting! Any ideas on how to remove a refactory cement?

I've had a rat bike (matt black too) before, but it seems strange to me that someone would do this to a nice-running, good quality and relatively new bike, rather than remove the exhaust, fix the exhaust and fit new exhaust gaskets.
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Riejufixing
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PostPosted: 21:55 - 03 Apr 2020    Post subject: Reply with quote
ThatDippyTwat wrote:
It's probably Fireclay - I used it a lot on the rat for this exact purpose.

Fireclay? That must be some Purimachos I have not seen before Smile Fire cement, which may contain fireclay, I don't know, would be useless for this!
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Scotsrick
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PostPosted: 07:38 - 04 Apr 2020    Post subject: Reply with quote
On the bright side cylinder heads for that engine can be bought for peanuts .

Even if the studs are borked it’s probably going to be easier swapping heads.
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ThatDippyTwat
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PostPosted: 09:05 - 04 Apr 2020    Post subject: Reply with quote
Bhud wrote:
Interesting! Any ideas on how to remove a refactory cement?


Heat cycle it a few times, prod it with stuff. It'll flake off. Think extra thick, sticky gungum. We use a Needler on it, but we also get it way hotter than your exhaust will (Molten steel), let alone your cylinder head. You want it good and hot. More vibration is better. Ask any woman about those two things.

If it doesn't flake off, then fuck knows what it is. As said, most epoxies will get gooey and reek, if not ignite at the temps on exhaust headers.

Reiju - Generic term.
If you know about the stuff, you know there's a fuckton of variations on it, depending on application. Some have binders that make it more resistant to vibration, some is single use.
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Bhud
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PostPosted: 13:18 - 04 Apr 2020    Post subject: Reply with quote
Scotsrick wrote:
On the bright side cylinder heads for that engine can be bought for peanuts .


The bike itself is priced otherwise (seller is not willing to let it go for project/nonrunner money). If I make it mine, I will be down the cost of the bike plus a new cylinder head, new cyl head gasket, set of valve stem oil seals, budgeting as well for new valve shims, plus (probably) new exhaust header bolts and threaded studs. The sum total for the bike and all these parts would be excessive for what it is.

Quote:
Even if the studs are borked it’s probably going to be easier swapping heads.


Well, there may be another way. That is, just ignoring the problem, riding the bike around as per normal once we're past the corona virus thing, and just waiting for the stuff to flake away with repeated heat cycles. However, I really don't like the mechanical inelegance of doing it this way.
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Easy-X
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PostPosted: 17:08 - 04 Apr 2020    Post subject: Reply with quote
If someone has done this to a bike then what other shortcuts have they taken? "Oh yeah, I ran out of motor oil but I had some leftover chip fat..."

I don't know what they're asking but I'd start the conversation with "It's a great bike but I'll have to get a new barrel, studs, gasket... maybe new downpipes. Taking that off the bill would leave the price at £xxxx and that's me doing the work for free!" No movement? Just walk away.
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Bhud
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PostPosted: 17:21 - 04 Apr 2020    Post subject: Reply with quote
Easy-X wrote:
If someone has done this to a bike then what other shortcuts have they taken? "Oh yeah, I ran out of motor oil but I had some leftover chip fat..."

I don't know what they're asking but I'd start the conversation with "It's a great bike but I'll have to get a new barrel, studs, gasket... maybe new downpipes. Taking that off the bill would leave the price at £xxxx and that's me doing the work for free!" No movement? Just walk away.


Yes, that's my worry. I've looked over the bike and it's a lot different from a Kawasaki (e.g. ER5). The thoughtfulness of the design (e.g. everything packed away in a logical place for ease of access) and quality of fit and finish and all the parts is really impressive. Nothing cheap or crap about any of it.

It seems that someone wasn't impressed with any of this, and, I agree, if they weren't willing to shell out a fiver for exhaust gaskets and instead did this to an obviously good quality bike, it doesn't reflect well on their attitude to maintenance and upkeep. There may be lots more gremlins under the surface. What surprises me is the way the carbs are in perfect sync and don't need my touch at all. Someone could be bothered to do that. Cosmetically, it's also very good. It has brand new tyres, the chain and sprockets are good (though the chain is slack). The bike as a whole is a mass of inconsistencies.
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