So Close!...
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Yeah. I just can’t imagine how the bottom end could affect the head seal. I thought it might be the budget price eBay Athena gaskets at one point. Changed to Vertex with same results. I’ve tried 3 different barrel & head combinations. I’m the only constant factor
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I even thought it was something to do with the engine mounts, especially the head one putting too much stress on it...
Then again I reach for just about anything to make sense of the ‘situation’
I put it back together with a new Vertex gasket and yet another, different, 3mb barrel, piston & 3mb head (£50, thanks eBay!!) Hoping this time it’ll last longer than 3~6 weeks!
...Did a 70 mile trip to shake it down with no hiccups
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@SpookDog Just been reading about your headgasket situation.
On another thread you commented that you've blocked off your carb warmer circuit using allen bolts and copper washers; potentially this means your cooling system is no longer self-bleeding when you refill the coolant (the stock thermostat has a small bleed hole but it's tiny, <1mm so there's no guarantee this isn't blocked).
If you have an air pocket right at the top of the head, the coolant may not be pressurising which will lower its boiling point and lead to overheating (and an air pocket will itself lead to a hot spot as there's less coolant there to carry away the excess heat). Possibly increasing the likelihood of your headgasket(s) to fail.
Try refitting the carb warmer circuit banjos so you can disconnect the hose at the thermostat housing until coolant free of air bubbles emerges when refilling the system (this is how Yamaha and Haynes recommend bleeding the cooling system). If you don't want the carb warmer circuit you can just run a hose straight from one banjo to the other so access to the carb isn't affected.
Considering how much trouble you've had with ebay gaskets etc., I'd also invest in a genuine Yamaha gasket and maybe a new thermostat (or at least remove yours and test it),
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2 weeks and still have a functioning head gasket and cooling system
I’m not counting my albatross’s yet but it’s looking good... -
Cheers for the input. I’ve tried various new and older but tested thermostats. I’ve tried different head nuts & washers. Studs locktighted and not, finger tight and cinched up tight. Tried the head to frame mount tight and ‘not tight’ thinking there may be too much stress on the head through the mount. I think I’m on my fourth different head & barrel combo. Using pure water at the moment, also changed my 2stroke oil thinking that there may be some kind of reaction between it and the gasket covering...
Gasket has always leaks at a different point. Always between the gasket upper surface and the head apart from the one time last time when it leaked both sides of the gasket...
Any idea or input is appreciated greatly, but yes I always put the gasket UP the proper way
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@SpookDog I am at a total loss as to why you're having so many problems.
Next thing we need to check is the compression. If you're running like million PSI compression then that would explain something.
I mean, these bikes were exported globally so you really shouldn't be having this much issue. They are also very basic and you really have to be doing something wrong to be having this much trouble.
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I’m hoping that it’s good to go this time. I’ve ran 3bn and different 3mb& 3mb-p heads. Nothing radical
...The thing is I been doubting myself for a while but I really can’t see anything wrong with my method...
If it fails again I’m gonna do a pic by pic slideshow of my methodology to see if anyone can point out anything obvious I’m missing... -
My only real doubt is my lapping technique for clean old gasket crap off and prepping the barrel top and head mating surfaces. I’m gonna get a new peice of plate glass and new wet n dry for future endeavours...
I might just get them skimmed/finished by PJME as well. I have a barrel that needs a new rebore and they were the best finish I’ve ever seen on the bore...
I’ll get there sometime soon. The bike is running better than it ever has before since I got the carb jetted proper. I just need to fit my new 3.50 rear tire and lower the gearing so it gets into the power band in 5th & 6th easier...
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@SpookDog What I mean is, if you're running a super thin base gasket, lapped the head a million times + lord knows what someone else did in its life, it could be running super high compression. You've somehow magically managed not to blow the engine up through detonation, but instead are blowing the head gasket...I am really clutching at straws here though.
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@SpookDog Crazy your gasket problems as done loads of engines and every head gasket from cheap white ones in those cheapo full gasket sets to athena gaskets and never had a problem. On barrels always use blowtorch on studs and 40 years working on 2 stroke engines and never snapped a stud yet. Remove studs then piece of glass with 240 wet & dry on barrel and head and 100% flat, I use my cooker hob as it glass really strong and it
doesn,t move about, just do mine when the wife is out.lol -
That’s the stuff! Old mirrors can be good as well
I always use heat for stud removal as well. The only time I didn’t I snapped a stud, it had only been in for 6 weeks and not even tight! In hindsight it was too new and shiny (came with a head and barrel I brought) and didn’t have the dimple on the top. Was a cheap fleabay copy I think...
I’ll have to try 240 drift. I can’t remember what I used before. A nice even Matt finish and a check with a steel rule is my usual MO. Head and barrel. The barrel base is more awkward but I use a square glass drinks coaster...
My latest iteration is still hold up. It’s been nearly a 1000 miles now
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I know, but I can’t figure it out! Not to blow my own trumpet, but I don’t think I’m doing anything wrong with my methodology or workmanship. It’s consistently lasting for weeks after fitting (about 1000 miles this time) If it was my idiosy it would fail straight away, not last 100’s of miles of normal use!
I’ve tried 3 or more different head & barrel variations. So it’s not the barrel or head to blame!
Tried different makes of gasket.
Ditto base gaskets for the barrel.
Different coolant, pure water combinations. Different 2stroke oils, ect. Just in case one of them was reacting with the gasket coating!
Different carbs. Different jetting combinations!...The only thing that is constant is the exhaust. I’m thinking this because there is always a rattling~knocking noise when I’m idling along at very low (but not closed) throttle in any gear. I thought it was piston slap at one point in time, but it’s done it with various barrel and pistons. It might be pre/miss~firing maybe? (I heard about a similar rough/flat spot that cleared up with an exhaust change) It kinda ties into a problem I’ve always had with a low rev stumble/flat-spot that happens when I crack the throttle slightly, that I always took to be a jetting issue that I could never resolve...
I’m really fuckin clutching at straws here, I know! I just can’t imagine what else could be causing this. I’m even thinking about building another bottom end
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