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 Post subject: Re: GT750 Thermostats
PostPosted: Wed May 31, 2017 10:55 am 
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Around the block
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Location: Fort Worth
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Bikes owned: GT750, GS1000s
i have been tied up by work so I haven't spent much time on mine since my last post.

From the sounds of things your bike has the exact same symptoms mine does.

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 Post subject: Re: GT750 Thermostats
PostPosted: Sun Nov 19, 2017 4:37 pm 
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Bikes owned: GT750, GS1000s
Still working like crazy, but fired up the bike took a spin and parked in the garage so I can work on it over the winter. I still have the last test to do, but I am pretty sure it is related to the head gasket.

When idling in the driveway after being run around the block, the makeshift anti-freeze bottle still bubbles but doesn't push any more antifreeze in to the bottle. Immediately after shutting off the bike off it bubbled for a 2 or 3 more seconds before stopping. When I slowly opened the cap it bubbled a lot into the bottle as the rest of the pressure was released. It was all air that bubble no more antifreeze.

The bike came with a ton of parts from Wayne including head gaskets. What is the difference between these? I also looks like the copper one has smaller holes for the pistons. Maybe one is for an over bored engine?

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Looking for anything else any of have to offer for suggestions before I start tearing into it.


Thanks!

Rich

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 Post subject: Re: GT750 Thermostats
PostPosted: Sun Nov 19, 2017 7:41 pm 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2171
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
Head gasket. Don't ask how I know - it still hurts.
Not sure how you pressurised the system, but a blown head gasket (into the cooling system) will put a helluva lot more than 30psi in it. The pressure in a non firing cylinder should be 120psi + and if that cylinder is firing, then multiply the static pressure several times - a second. Remember 1200rpm (fast tickover) is 20 revs per second so the pressure that goes into the cooling system is very high. Just get a new head gasket and fit it.
Might be an idea to check static pressure (no plugs in any cylinder) in all 3 cylinders first.


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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Nov 20, 2017 10:53 am 
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Location: Illinois
OEM and aftermarket head gaskets are made with over sized bores to cope with the fact that bores do not always appear to be in the exact same places. Copper ones and COMETIC are made to the size you specify.

AN oversized gasket leaves a rage annular are that doesn't burn at all and tends to detonate leading to blown head gaskets. I am not a fan of copper gaskets because it's hard to get them to seal properly over such a large head. The best gaskets available IMHO are from COMETIC in Ohio

I have some more OEM gaskets and Athena and others that will never be used. Pass them on to the next owner as spares......


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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Nov 20, 2017 12:07 pm 
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Location: Fort Worth
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tz375 wrote:
OEM and aftermarket head gaskets are made with over sized bores to cope with the fact that bores do not always appear to be in the exact same places. Copper ones and COMETIC are made to the size you specify.

AN oversized gasket leaves a rage annular are that doesn't burn at all and tends to detonate leading to blown head gaskets. I am not a fan of copper gaskets because it's hard to get them to seal properly over such a large head. The best gaskets available IMHO are from COMETIC in Ohio

I have some more OEM gaskets and Athena and others that will never be used. Pass them on to the next owner as spares......



So are you telling you wouldn't use either of the gaskets I already have? If not, I guess I need to get the head off and measure the bores and have Cometic make one to size for me?

I'll freely admit this thing being water cooled and having one big head has me spooked more than a little. If this was my old AIR Cooled H2 Kawi it have been apart and fixed a long time ago.

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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Nov 20, 2017 1:10 pm 
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Location: The Republic of South Yorkshire
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Bikes owned: GT550s GT750 GSX1400 and lots of spares
simmons1 wrote:
I'll freely admit this thing being water cooled and having one big head has me spooked more than a little. If this was my old AIR Cooled H2 Kawi it have been apart and fixed a long time ago.


Dunno why, nearly every car engine in the world is like that - and lots of bikes too.
Yes that Kaw will be easier, but then again, I've never had issues with GT550 heads not sealing.
I've had a few apart since 1973 or so and they are one piece across 3 pots.


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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Nov 20, 2017 2:39 pm 
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Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Alan H wrote:
Yes that Kaw will be easier, but then again, I've never had issues with GT550 heads not sealing.
I've had a few apart since 1973 or so and they are one piece across 3 pots.

I have heard on here of few problems with the 1-piece heads. According to some they have a tendency to become incorrectly torqued and start leaking over time. I have no personal experience of this.
I have plenty of experience with car engines and on those, head gaskets often fail if they have been replaced without skimming the head.
It is worth skimming or at least checking for warping while rebuilding. Make sure you remove all traces of old gasket when you rebuild and that there are no deep scratches/damage on the mating surfaces.


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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Nov 20, 2017 5:11 pm 
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Location: Illinois
Let's back up a bit. I would use a copper gasket in certain applications and that includes a race GT750 with inserts/domes but they are hard to seal the water in and tend to warp over time.

On a stock GT750 that's not had the compression raised and is not thrashed to way past the stock redline, an OEM gasket will be fine and so would any aftermarket gasket.

For a ported/high compression motor or one that is ridden hard, I would only use Cometic. Mine live between 6 and 9k for 13 seconds at a time, so I need to stick teh parts together nice and tight and Cometic gaskets do that. They stick like sh#t to a blanket as they say.

GT550s have an inherent problem that the barrels are three pieces and they can expand differently when ridden hard and that can cause issues. They have 3 gaskets - one per cylinder and for a fairly stock motor, I'd prefer to keep a one piece head. Ridden hard, I'd probably split the head. The 750 is different in that it has a very stiff (and heavy) cylinder block and enough hardware to keep it all together under normal operating conditions.


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 Post subject: Re: GT750 Thermostats
PostPosted: Thu Nov 23, 2017 6:30 pm 
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Location: Fort Worth
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Bikes owned: GT750, GS1000s
Head is off. I am guessing it is leaking near the bolt with the corrosion. Also looks like it has a copper gasket. Could one of you smarter than me guys comment on these photos. I can take more photos if necessary.

The spare copper head gasket is the same size as the bore. The grey one is quite a bit bigger.

Thanks!


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 Post subject: Re: GT750 Thermostats
PostPosted: Thu Nov 23, 2017 9:53 pm 
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Location: Illinois
Yep, that's a copper gasket and they leak. Get one for Cometic to whatever bore size you want and live happily ever after.

It doesn't look like there has been a lot of blow through, so I would just clean it all up, have the head shaved to get it flat and fit a new gasket.

If you absolutely have to use a copper gasket, it must be sealed with a suitable sealer.


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 Post subject: Re: GT750 Thermostats
PostPosted: Thu Nov 23, 2017 10:25 pm 
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Location: Fort Worth
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tz375 wrote:
Yep, that's a copper gasket and they leak. Get one for Cometic to whatever bore size you want and live happily ever after.

It doesn't look like there has been a lot of blow through, so I would just clean it all up, have the head shaved to get it flat and fit a new gasket.

If you absolutely have to use a copper gasket, it must be sealed with a suitable sealer.


I will buy a Cometic next week. The head came off real easy, and the copper gasket wasn't stuck real well on either side. I am guessing this was the problem since day one with Wayne. Would like to get Buffalo finally squared away and use a thermostat for the first time.

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 Post subject: Re: GT750 Thermostats
PostPosted: Fri Nov 24, 2017 8:38 am 
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Just tried to navigate Cometic's website. Do I have to call them to order a Buffalo head gasket?

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 Post subject: Re: GT750 Thermostats
PostPosted: Fri Nov 24, 2017 9:07 am 
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Yes, you need to call them to order the diameter you want.

For a 1mm thick, 71mm bore gasket I have a part number of H1247SP2043F it says description: 362484. That was from the packing on the last one I fitted.


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 Post subject: Re: GT750 Thermostats
PostPosted: Mon Nov 27, 2017 10:20 am 
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Location: Fort Worth
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Just ordered 2 head gaskets from Cometic. Painless process. $51 and change each. I will have a spare for the future if I ever need one.

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 Post subject: Re: GT750 Thermostats
PostPosted: Thu Nov 30, 2017 9:46 pm 
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Joined: Tue May 06, 2014 8:21 pm
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Location: Fort Worth
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Bikes owned: GT750, GS1000s
New heads gaskets arrived today.

I checked out the head using a straight edge and feeler gauge like shown in the manual. The head looks to be very flat. There was one place that had an .001 or touch larger gap under the straight edge. It was in the area of the head where the stud in the cylinder goes through the head.

Can the head be used as is or does it need to be resurfaced? The reason I am asking is that I am afraid of damaging the head removing the bypass fitting. It is really really tight and appears to be corroded in place.

Thanks!

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