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Location:
Adelaide
Registered:
May 2002
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my Hybrid engine Question: Please help :)
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Mon, 29 July 2002 09:27
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Hey all
ive got a question (and i'm sure it has been answered) and its about my hydrid engine 2TG yamaha head on a 3T block.
Well i know i have to flycut the exhaust relief valve spot on the 3T pistons BUT what i really need to know is the dome shape on the 3T pistons.
On the 2TG pistons it has an offset of 10mm (or there abouts) and the head is also offset. (as people prolly all know hehe)
Does anyone know if i have to shape the 3T piston same as the 2TG pistons so i wont F*** my head up? Will the 3T piston even touch my head (coz ive just reliesed the head gasket might make a little bit of clearance also)
Please any, I mean ANY info on doing this would be very much appreciated as i'm just about to put it all back together 
Thanks Simon
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Location:
Adelaide
Registered:
May 2002
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Re: my Hybrid engine Question: Please help :)
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Mon, 29 July 2002 10:36
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ok, it's a bit of trial and error kinda thing.
I have done this kinda engine three times and each time the clearance was different...... the first time we had problems cos there wasn't enough clearance, we found this out by the valve guides getting broken by valve bounce, but it also turned out that the head we used had been shaved/faced a fair bit, and to top that the block used had been decked as much as you could, therefore everything was so close together......
second time, cos there were some destroyed pistons we had to get a new set, so we made the flycuts the same depth as the first time, which turned out to be plenty of clearance, we also had a different 3T block this time, they put some plastecine in the vlave releifs and turned the engine over, pulled it apart and there wasn't a mark in the plastacine, so there is now plenty of clearance....
so yeah hard to say... unless you know exactly how much has been taken off of your head and the top of your block.
so if ya got the time it might be an idea to throw some plastacine in there and put it together and turn it over, pull it apart and have a look.....
Brendon
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Location:
Adelaide
Registered:
May 2002
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Re: my Hybrid engine Question: Please help :)
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Mon, 29 July 2002 10:44
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hehe Thx for the info
I'm pretty sure the inlet side is/will be deep enough for sure.
Should i get the exhasut side same depth as inlet?
Also the dome sizes on the 3T pistons... u didnt have to do anything with that?
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Location:
New Zealand
Registered:
May 2002
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Re: my Hybrid engine Question: Please help :)
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Mon, 29 July 2002 10:47
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Jonny has posted before that the exhaust valve relief would need to be cut to the same depth as the intake valve relief.
Of course, this would all change with cams... which every good 3TG motor should be running  .
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Location:
Adelaide
Registered:
May 2002
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Re: my Hybrid engine Question: Please help :)
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Tue, 30 July 2002 04:13
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well I have SEEN my pistons and both sides look about the same, so yeah I presume they are the same depth......
and very true about the cams, no point having all that more capacity if ya aren't gonna do anything up top..... which reminds me I really need to get mine measured so I know what specs they are....
Brendon
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Location:
Adelaide
Registered:
May 2002
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Re: my Hybrid engine Question: Please help :)
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Tue, 30 July 2002 10:25
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Well. today i put blue tack (haha didnt have any plasticene) on my pistons to see what would happen and i guessed it.. the dome on the 3T pistons are waaaaay to big (in width) accross the top of the piston.
Me thinks i have a different head (newer version of the yamaha head) because the doem on my old 2TG pistons is offset and ALOT smaller...
I just hope there is the same about of meat on the 3T pistons as my 2TG coz i'm gonna get an engineering mod to do all of this work (not gonna cost heaps tho)
anyways more info would be very much appreciated..
Cheers Simon
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