Coolant loss
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@spookdog the radiator will draw a vacuum when the coolant cools and contracts. Typically the amount the coolant expands and contracts is pretty minimal however. I have had coolant come gushing out of the expansion bottle when my head gasket had faoled. I used a cheap pattern gasket and it didn't work.
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Check your radiator cap and where the cap seals on the radiator. Had a rad that with a small bit of damage where the inner part of the rad cap seals against. Which meant water would flow to the expansion bottle as soon as it warmed even a little.
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@dtr-nsr
I was wondering about that. I can’t work out how the coolant flows back in past the inner seal. I’ve cleaned up the inner surfaces and I have a spare cap somewhere I think. I’ll give it another test ride. I’m just hoping it ain’t the head gasket, it’s an Athena with 3000 trouble free miles on it. The only new gaskets I have are copper, I’ve no experience with them... -
@spookdog if you look at the under side of the cap you'll see a little metal washer that you can pull down, that's spring loaded. When your coolant cools and contracts, it creates a vacuum pulling down that washer allowing coolant to flow back in to the rad.
Not had great success with copper gaskets myself, tend to be alot thicker as well, lowering the compression. -
@dtr-nsr
Nice! I see what you mean now and can make sense of it in my mind. It was bugging me not understanding how it works...I believe that you’re supposed to re~torque the head nuts again after a certain interval/good run? I think I may of omitted to do this
it was such a long time between fitting the head and riding the bike or bringing it up to temp that I can’t be sure. I can see the path where it burned off the black coating from the gasket. I blame myself rather than Athena 
I’ve got a 0.5 & a 1mm copper gasket. I’m gonna try the .5 cause the head is 0.5mm deep to the squish. It’ll give me something to do till I get another Athena...
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Are the composite gaskets much thicker than the metal shim gaskets? I’m wondering about it affecting the squish band gap.
I got 200 miles out of the Chinese one I had kicking around. I have to try the copper one now, with Hylomar to fill the gaps. Just till I get some pennies in my pockets. Or unless the copper on is a keeper -
This is weird, I was seeing lots of gaskets made of composite for dtr’s (125) made by Athena. Now i can only find one and that looks like they used a 170 pic for the listing.
Do Athena make composite gaskets for a 125? Or is it just 170?... -
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@calum
Cheers bud...
2 nm’s is where my wrench kicks in. It’s too near the threshold for me to trust. If I want to do it right I really want new studs and dome nuts with washers.
I’ve never had troubles with single cylinder bikes before, then again none of them were liquid cooled... -
Thoughts please!...
3 times now my head gasket has blown. The first time it was a good gasket with 3000 miles on it, the 2nd time it was a cheap Chinese job that was ‘used but not run’. 3rd time was using an unfamiliar copper gasket without the proper spray sealant, so the last 2 are on me.
Each time it failed in a different place, but! the weird thing is that it always failed on the upper, head side of the gasket. The bottom half was always sealed firmly to the barrel, with absolutely zero sign of leakage or blow by. Any ideas why?... -
@calum
It ran sweet for 3000 miles then blew. I didn’t reuse it. It was new & Athena. I just got another delivered today for under £13 which I thought was quite good...Yeah, the up is on the up
its weird that they all blown at the head side of the gaskets...
Is my squish supposed to be less than a mm, with gasket included?...
The head was done by PJME 3000 miles ago. I’m thinking of maybe lapping it on a good bit of plate glass -
I’m gonna have to check it out. My brand new Athena gasket, correctly torqued down, blew again
️ Did about 100miles. Weird thing is that the bike ran the best ever after it let go. Crisp rev definition, no bogging down. I’m gonna have to compression test the engine next time. What range is good/normal!?
