So Close!...
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@SpookDog I know that bud but they are set so they open at a certain pressure and different caps are set to different pressures due to different strength springs (dt125r cap should open at 12.8psi with a tolerance of +/-1.5psi) and if it's old and worn and opening too soon/late then it won't regulate the temperature correctly. Springs tend to weaken as they age. It's surely a coolant issue you have. I may well be wrong but given the trouble you've had a £15 cap is surely worth a try?
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@markus-w
Hey! Don’t get me wrong, I appreciate all and any ideas. I’ve got 3 old, original caps. I’m definitely gonna find an New original one just to be sure that I cross i’s and dot the t. But I’m not sold on it being the cause.
I’m doubting my own workmanship more at the moment... -
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One thing that I’ve never done is re~torque the head after riding the bike up to temp. I’ve just put a ring spanner on the head nuts and given them a tweak. It was surprisingly easy to tighten them (Very surprisingly easy!!) Looking back it was never hard to undo them when tearing down the top end. I haven’t seen anything about re~torquing in the Haynes. Only ever seen it recommended with car head gaskets that are those silver multi layered ‘compressible’ stuff...
Does everyone else retorque after running up to temp?...
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@SpookDog haha my suggestion to you, hopefully it works , I know it is really a car thing but in theory heated metal expands especially alloys, be nice to know what the torque wrench says with it heated vs what It said unheated although hard to get one in a built bike
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@MH-Bikes-N-Bits using a 1/4" drive torque wrench (£20-£30 from a cycle shop) and 1/4" drive universal joint and 12mm socket you can get to all the head nuts with the engine in situ, even the one at the front which is close to the frame.
Alternatively you can remove all the engine mount bolts apart from the swingarm pivot and rotate the whole engine around it a few degrees to improve access (I did this once to replace the O-ring in the steel water pipe without disturbing the waterpump cover as I had reason to believe one of the cover bolts was seized)
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That’s been circling around my noggin for a while. There was a thread about someone getting it done at PJME but I never saw any follow up. Interested in knowing the price. I’ve got a 4fu barrel I wouldn’t mind getting sleeved by them as well...
@ mikes bits
I did remember someone saying about re-torquing the head
Is it after it’s been run to temp then cooled down? I wouldn’t do it while hot!...@ hotshot
I’ve never done it before, but the nuts were not super tight, so it got me wondering...I remove the bottom and front mount bolts, loosen the swing arm bolt and lift the front of the engine with a big screwdriver. Once you’ve taken off the thermostat cover you can get in there nicely with a 1/4 drive torque wrench
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@SpookDog said in So Close!...:
One thing that I’ve never done is re~torque the head after riding the bike up to temp. I’ve just put a ring spanner on the head nuts and given them a tweak. It was surprisingly easy to tighten them (Very surprisingly easy!!) Looking back it was never hard to undo them when tearing down the top end. I haven’t seen anything about re~torquing in the Haynes. Only ever seen it recommended with car head gaskets that are those silver multi layered ‘compressible’ stuff...
Does everyone else retorque after running up to temp?...
After about little run in on the first km's I check every bolt and re-torque the head and cylinder.Almost every time was ok,one time one headbolt need it a little more but nothing serious.
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@MadGyver
Cheers geez, it’s all good to know. I didn’t think it was absolutely necessary, but there you go. No two situations are exactly the same...@anyone
I’ve gotten myself a new piece of plate glass (6mm was thickest I can get locally) and loads of fresh w&d from 80grit on through to 600. I’m gonna have one last go and give the head (especially) and barrel a good lapping. If it fails after this I’m gonna get a good 3mb head cnc grooved for orings (is it one or two on a standard head? I still want to know why it’s good for about a 1000 miles before it fails. I would imagine it’d fail sooner if it was poor finishing of the mating surfaces? But, hey ho! One problem at a time! I will get both surfaces skimmed if I can find a good local engineer that hasn’t lost practice cause of Covid
I still want to build another bottom end when I can afford genuine seals and bearings all through. I’ll never buy non genuine fleabay again, that’s for sure. I prefer my Crap Shoots to happen in a Casino!
...Good luck to the people’s with problems, love to all else!
️
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Just took of the head and the gasket failed at the back of the head, passing pressure to the big coolant opening on the gasket (the others are just 4mm holes) at the mounting point. It’s failed there a few times. I don’t have an original bolt at the front engine mount point, just an Allen bolt. I’m wondering if it’s putting stress on the head mount. Or if it’s just the easy/biggest target?...
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Whacked on another Vertex I had laying about. It was a reject to start cause of very slight creasing, but beggars are not the choosiest!
I did give the barrel a good clean/lap. The head I gave extra attention with 150 grit...Did a 70 mile run in test, nothing over 6k rpm. Temp right on the 60degC thermostat ‘just opening’ spot on the temp gauge. During the hot weather it was up on the 80degC ‘wide open’ spot. It was like trying to cool the radiator with a hairdryer!!...
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10 days and about 700 miles later the radiator level is starting to drop, expansion tank over spilling. This is like fucking clockwork. I just can’t get my head around it!
I’m going to have to get a head professionally skimmed, as well as a barrel...
I also need to find out how much someone like PJME charge for an o~ring conversion...I’ve only recently found out that you can still get Yamaha DTR125 genuine head gaskets!? I read somewhere that they are thick ‘rubber coated’? I just assumed that they had the same thin black coating that Vertex or Athena head gaskets have and you payed a premium for the Yamaha name? Has anyone seen/used a £40 genuine gasket and can give comparison with Athena or Vertex, similar, gaskets?...
It would be a big help
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@SpookDog said in So Close!...:
10 days and about 700 miles later the radiator level is starting to drop, expansion tank over spilling. This is like fucking clockwork. I just can’t get my head around it!
I’m going to have to get a head professionally skimmed, as well as a barrel...
I also need to find out how much someone like PJME charge for an o~ring conversion...I’ve only recently found out that you can still get Yamaha DTR125 genuine head gaskets!? I read somewhere that they are thick ‘rubber coated’? I just assumed that they had the same thin black coating that Vertex or Athena head gaskets have and you payed a premium for the Yamaha name? Has anyone seen/used a £40 genuine gasket and can give comparison with Athena or Vertex, similar, gaskets?...
It would be a big help
...Have you used custom copper gasket with copper gasket spray,they used it for high compression and performance engines,you can anneal the gasket to become softer and sit even better.
You probably burn slowly coolant and venting pressure in the cooling system.
I only use yamaha or custom copper head gaskets+copper spray.
