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Post by urbantangleweed on Oct 26, 2018 19:15:08 GMT 1
OK, fully rebuilt a YPVS engine, new everything, re-bored barrels, new pistons, all put together with love, care, much attention to detail and pressure tested. Ran it up to temperature, left to cool, re-checked head bolt torque and all good at 20lb/ft.
A couple of short shake down runs and everything seemed fine, then on a longer run, after about 12 miles, pulled over to give her the once over and at switching off the engine it instantly boiled and a cloud of steam came from under the tank, bad end to the day and she came home in the back of a van!
On further investigation, no apparent coolant leaks (after re-filling the system) but running with the rad cap off, fine on tickover, but raising the revs to 2-3000 the coolant visibly reduced down the filler neck, even with regularly topping up hoping it was just bleeding air out the system. Still no apparent leaks so assumed head gasket (pattern...yeah, I know.....) wasn't doing what it should and assumed coolant was being drawn into the cylinder(s) and spat down the exhaust(s). Head bolts still at 20lb/ft, snuck 'em up to 21, no change.
Took the bull by the horns, head off, checked for flatness on glass, not perfect but not bad, maybe 0.1mm out in places, anyway, not one for messing about the head was skimmed, checked again and perfectly flat. Barrels checked for equal level, all mating surfaces made spotlessly clean and all seemed well. Rebuilt with genuine gasket and can't believe the same thing appears to be happening.
Still no apparent system leaks and no water in the gearbox oil suggests water pump seal (new, gen Yam) is good, any ideas where to look now?
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Post by midlifecrisisrd on Oct 26, 2018 19:39:29 GMT 1
Are you torquing the head bolts before the base nuts?
Had one years ago that was the same and this was the only thing that sorted it
Now do it on all my builds
Steve
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Post by midlifecrisisrd on Oct 26, 2018 19:41:48 GMT 1
Should also say you won't always see water leaking into the cylinder
The combustion pressure leaks into the water jacket pressurising it
After 0.9 bar the cap opens and let's the pressure off into the expansion tank which overflows
Steve
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Post by urbantangleweed on Oct 26, 2018 19:45:16 GMT 1
Are you torquing the head bolts before the base nuts? Had one years ago that was the same and this was the only thing that sorted it Now do it on all my builds Steve So finger tighten base nuts, torque head then tighten base nuts? |
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Post by urbantangleweed on Oct 26, 2018 19:47:01 GMT 1
Should also say you won't always see water leaking into the cylinder The combustion pressure leaks into the water jacket pressurising it After 0.9 bar the cap opens and let's the pressure off into the expansion tank which overflows Steve This could be happening, I'll make a study tomorrow. |
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Post by midlifecrisisrd on Oct 26, 2018 19:47:24 GMT 1
Are you torquing the head bolts before the base nuts? Had one years ago that was the same and this was the only thing that sorted it Now do it on all my builds Steve So finger tighten base nuts, torque head then tighten base nuts? Exactly! The theory is any tiny difference in deck level or case level is taken up with the base gaskets Steve |
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Post by midlifecrisisrd on Oct 26, 2018 19:48:33 GMT 1
New base gaskets required mind
4l04ever does some nice Siamese ones cheaper than genuine
Steve
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Post by urbantangleweed on Oct 26, 2018 19:54:09 GMT 1
New base gaskets required mind 4l04ever does some nice Siamese ones cheaper than genuine Steve Full top end strip, again!  |
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Post by urbantangleweed on Oct 26, 2018 19:55:25 GMT 1
What about having the head O ringed?
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Post by midlifecrisisrd on Oct 26, 2018 19:56:55 GMT 1
Yes that is an option
I know stusco had constant probs with his so ended up with a cool head
Steve
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Post by Tobyjugs on Oct 26, 2018 20:07:41 GMT 1
I wonder if it has anything to do with the water pump?
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Post by urbantangleweed on Oct 26, 2018 20:18:49 GMT 1
I wonder if it has anything to do with the water pump? Me too, so I took the cover off to check the impeller was turning and it was, tried to hold it as firmly as possible then turn the engine over with the kickstart and it still felt fine. Did you have something else in mind I didn't think of? |
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Post by Tobyjugs on Oct 26, 2018 20:28:14 GMT 1
I wonder if it has anything to do with the water pump? Me too, so I took the cover off to check the impeller was turning and it was, tried to hold it as firmly as possible then turn the engine over with the kickstart and it still felt fine. Did you have something else in mind I didn't think of? It's just the symptoms you described with the instant steam when you switched the engine off. I have had a similar problem with a V8 rover engine. It was the combination of a dodgy water pump and a faulty pressure cap which was releasing the pressure in the cooling system randomly. |
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Post by urbantangleweed on Oct 26, 2018 20:42:33 GMT 1
Me too, so I took the cover off to check the impeller was turning and it was, tried to hold it as firmly as possible then turn the engine over with the kickstart and it still felt fine. Did you have something else in mind I didn't think of? It's just the symptoms you described with the instant steam when you switched the engine off. I have had a similar problem with a V8 rover engine. It was the combination of a dodgy water pump and a faulty pressure cap which was releasing the pressure in the cooling system randomly. Good points, but that doesn't explain why the coolant buggers off with the engine running, usually it stays at a level with the rad cap off and then expands with heat until it overflows? |
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Post by Tobyjugs on Oct 26, 2018 21:40:42 GMT 1
Hmm the coolant must be going somewhere. Try Steve's suggestion first.
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Post by muttsnuts on Oct 26, 2018 21:50:17 GMT 1
does the coolant level remain low when the engine is turned off, also which model is it as the 31k's are a pain to bleed all the air out of, no idea why they are worse than the others, but always careful with those as had air lock issues a few times on them. the water disappearing when revving up is normal to a point, but the level should return when the engine is stopped unless its air locked.
if you unsure, then the coolant system on a YPVS holds approx 1.5lts of water, so before you strip the engine down, drain it all out as best you can, seal back up and then measure the quantity you can get in, unless you have 1.5lts then you have air locking, if you keep topping it up (again measuring the amount), if you go past 1.8/1.9lts then you have a problem, if you don't, then its all fine. If its spitting it out of the overflow tank under pressure then you have a head leak issue
HTH
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Post by urbantangleweed on Oct 26, 2018 22:05:44 GMT 1
does the coolant level remain low when the engine is turned off, also which model is it as the 31k's are a pain to bleed all the air out of, no idea why they are worse than the others, but always careful with those as had air lock issues a few times on them. the water disappearing when revving up is normal to a point, but the level should return when the engine is stopped unless its air locked. if you unsure, then the coolant system on a YPVS holds approx 1.5lts of water, so before you strip the engine down, drain it all out as best you can, seal back up and then measure the quantity you can get in, unless you have 1.5lts then you have air locking, if you keep topping it up (again measuring the amount), if you go past 1.8/1.9lts then you have a problem, if you don't, then its all fine. If its spitting it out of the overflow tank under pressure then you have a head leak issue HTH Thanks Dave. Level does stay constant if not running, topped it up this morning and standing all day the level is the same tonight. Model is 1WT and I originally filled it with 1.5 litres, then ran it, bled it, added probably another 100 ml, then another, then another....probably put 2 litres in before accepting it wasn't fixed, I'm guessing there's half a litre or more of coolant in the exhausts now. If I can get a strong mate over tomorrow, might try lifting the front end high and see what runs out. Also, and just for fun, I might pull the head off, smear hylomar over the gasket and put it back together to see if it proves a head gasket issue. |
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Post by urbantangleweed on Oct 27, 2018 9:14:40 GMT 1
Just an extra thought, would it be safe or of possible benefit to re-torque the head bolts to 22 lb/ft? Studs are standard and head bolts/washers are SS from Norbo.
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Post by headcoats on Oct 27, 2018 11:41:10 GMT 1
Have you been re torqueing the head after a few heat cycles as they go out of spec ?
I have gone up to 24 foot pounds with mine
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Post by looey on Oct 27, 2018 12:49:34 GMT 1
If it's any help, this is what I always do, even re-using same genuine head gasket over and over.
Some will disagree using a sealant of any kind, but I do and never had a head gasket leak.
I always a genuine Head Gasket with the thinnest smear possible of RTV clear silicone.
I do the barrel nuts up finger tight (no spanners), then torque the head down (23lb/ft), then tighten the barrel nuts. Then I run it for a couple of mins without any coolant in until the barrels are quite warm (but nowhere near hot), then I let it cool all day or overnight, then re-torque, then fill with coolant.
Works for me.
Good luck
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Post by steven on Oct 27, 2018 13:37:15 GMT 1
Hi,
Drain the coolant.
Fit an air line, and a pressure gauage, idealy with a pressure regulator, to the vent pipe fitting on your radiator.
Fit the radiator cap and pressure test the cooling system.
If its a big leak you will hear it, some soapy water on a paint brush will find smaller leaks.
Once you are happy its air tight, adjust the pressure regulator until the radiator cap opens and note the pressure....is the radiator cap opening at the correct pressure ?
I never used to, but I always pressure test my cooling system now after doing the leak down tests.
I tested all my radiator caps, and found several that were U/S.
Steven.
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Post by urbantangleweed on Oct 27, 2018 13:58:38 GMT 1
Been toying with it today and torqued the head bolts to 22, ran it and it seemed better, not fixed, but better. Then got my big pair of balls out and torqued the head bolts up to 25. Nothing sheared and it might have done the trick. Just ran it up to temperature and leaving it to cool down, will see where the level is in a bit.
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Post by bazzer5115 on Oct 27, 2018 16:31:13 GMT 1
I always start mine with no water,allowing it to get hot to the touch.
After cooling I re torque the head then fill with water.
Doing it this way,if you look very closely with a torch you can see where the Yamaha sealant on genuine gasket has melted/sealed between head and barrels 👌
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Post by headcoats on Oct 27, 2018 16:53:36 GMT 1
The question is , what is the magic goo they put on the genuine gaskets and can you buy it in a tube !
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Post by urbantangleweed on Oct 27, 2018 18:18:23 GMT 1
Well I've ran it up to temperature 3 times today, the last time, just now, let it go to 100c, if that don't melt the goo nothing will! See where the level's at in the morning and go from there.
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Post by mattybeckett on Oct 27, 2018 19:10:26 GMT 1
The question is , what is the magic goo they put on the genuine gaskets and can you buy it in a tube ! Yes. Same as this ;-)  |
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Post by mikee on Oct 27, 2018 19:26:41 GMT 1
Yamabond , 3 bond , avoid anything hylomar/hylobond etc
Mike
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Post by urbantangleweed on Oct 28, 2018 17:54:47 GMT 1
24 miles this afternoon, so far so good.
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Post by Tobyjugs on Oct 28, 2018 18:26:40 GMT 1
Yamabond , 3 bond , avoid anything hylomar/hylobond etc Mike HI Mike can you explain why it's best to avoid the above? Curiosity not a dig. |
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Post by earthman on Oct 28, 2018 20:40:51 GMT 1
Yamabond , 3 bond , avoid anything hylomar/hylobond etc Mike HI Mike can you explain why it's best to avoid the above? Curiosity not a dig. I'd like to know the reason(s) too.  |
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