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Old 08-24-2016, 02:05 PM   #11
dt400eman
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Any head you get will need the cutaway on the left side or you could just grind one in if it doesn't have one on the right side. Don't want to lose too much fin area. By clicking on the gasket part no.'s in the list below might get you a fairly accurate picture of the heads, but as in the 78 250 I could not see the cutaway on the left. Other pict's were usably accurate. Found this 78 DT250 head on e-bay.
http://www.ebay.com/itm/1978-YAMAHA-...ZXkP9R&vxp=mtr
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Old 08-24-2016, 04:17 PM   #12
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Looks like the 77 DT250 has an uncorrected compression ration of 6.7 to 1, while the larger cousin- the DT400 is 6.4 to 1. I could not find the specs for the 77 or 78 yz250 or 400, but the 77/78 IT250 has an uncorrected compression ratio of 7.8 to 1. I imagine the yz250 could be similar. That's a good bump in compression. Notice the yz has an offset combustion chamber which is supposed to help with exhaust side heating of the squish end gases over the exhaust. I believe an IT head has the exhaust looped around over the left side of the cylinder and I am not sure why they don't share the same head gasket. I don't see why an IT 250 head would not work. Maybe someone would know for sure, as this would give you more head options.
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Old 08-24-2016, 08:45 PM   #13
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Why performance has no edit feature is unclear to me. Anyhow in post #11 I had a typo- I meant 78 yz250 in both instances.

By clicking on the gasket part no.'s in the list below might get you a fairly accurate picture of the heads, but as in the 78 250 I could not see the cutaway on the left. Other pict's were usably accurate. Found this 78 DT250 head on e-bay.
http://www.ebay.com/itm/1978-YAMAHA-...ZXkP9R&vxp=mtr
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Old 09-01-2016, 12:00 PM   #14
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So, I bought the '78 YZ250 head from ebay for $29.95. We'll see how that works. I'm buying parts way ahead of time too. I have a couple of other bike projects further up in line.
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Old 09-01-2016, 04:40 PM   #15
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Cant wait to see how that head will work out. The heads unique design and higher compression have me very interested in the outcome. I bet it will work out well. Let us know when you get around to installing and said results.
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Old 09-02-2016, 11:42 AM   #16
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I WILL post the results - but it's gonna be a while. Like I said, a couple other bikes are ahead in line and I decided to start buying parts for this one too. It pays to scan ebay for super deals! I think parts for 70's bikes are DROPPING in price. They really aren't old enough to be "collectors" bikes and I think the sellers of these parts would rather sell them for a decent price than hold on to them for another 10 or 20 years.
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Old 09-02-2016, 11:49 AM   #17
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I am like you my brother. I try to buy ahead of time for projects coming up. As Enduronut said to me one time- Great minds think alike.
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Old 09-08-2016, 08:57 AM   #18
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Well, I received the head, a very pristine one (for a used head) but I have one question. As you mentioned, dt400eman, the combustion chamber is slightly offset in one direction. BUT, since I'm not that familiar with a '78 YZ250, which way does that head go on? I'm quite sure it could be mounted either way - combustion chamber area toward the front or back. The head does have some fins shaved down, for pipe clearance I'm sure, but that still doesn't tell me which way it goes on. BTW-I had the price wrong. It was $27.95 with free shipping.
Thanks!
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Old 09-08-2016, 12:04 PM   #19
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The wide part of the squish band must go towards the front(exhaust) of the motor. It's purpose is to help cool the hottest part of the engine, the exhaust side of the crown- directly under the fire of exiting exhaust gases through the exhaust port. It does this by trapping the relatively cool squish gases near the crown over a much larger area than center dome heads. It also shields the front part of the crown from combustion until a little later. I understand a squish bands effectiveness can be enhanced by closing the squish up to specs, but may still work if not.
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Old 10-29-2016, 09:58 PM   #20
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i installed a 78 YZ 250 head on my 78 DT 250 and it worked ok until i went for a longer ride (about 1/2 hour ) i started hearing noises like rod getting louder and i changed back to old head these motors are to old and unless you plan on rebuilding your motor often . i did not think it was worth the slight gain in power
good luck
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