Sawing my head in half..

[daxman]

.. well strictly speaking the 250A head..

Is it recommended? Somehow it doesn't feel right to have two piece barrels and one piece head.
Thoughts?

[jabcb]

The GT380s & GT550s have 3 separate cylinders & a one piece head. Worked out fine.

[Craig380]

On my 380 I had constant problems with the head bolts loosening over time, they needed re-torquing regularly to stop the head gaskets leaking. This eventually caused a couple of the head studs to strip the threads in the barrels (steel stud in ally barrel x 30+ years of heat cycles, etc).

I reckoned the bolts were loosening because the individual barrels were moving a little beneath the one-piece head casting, and the slight movement was causing the nuts to loosen (despite using new lockwashers and nuts, and OE head gaskets).

While having the barrel stud holes helicoiled, I asked the machine shop to cut the head into 3 pieces. I figured that if individual heads were good enough on the Kawasaki triples (which are in a higher state of tune) then the 380 should be fine.

Slapped it all back together, the head bolts never needed re-torquing again. Bike ran great.

[daxman]

I believe the 250 K,L,Ms also had individual heads so I'm wondering the reasoning behind the change for A,B,Cs..

[dollydog]

cheaper to make one head, rather than 2?
cheers, dd.
p.s. i've got a 'set' of 380 heads somewhere doing nowt

[Craig380]

I believe the 250 K,L,Ms also had individual heads so I'm wondering the reasoning behind the change for A,B,Cs..

The A/B/C models were in a (slightly) higher state of tune, the cylinders were revised and had an extra pair of transfer ports, there was also a compression change, 28mm carbs (up from 26mm), different exhausts and the crank got an extra main bearing between the cylinders.

But despite all the changes, I recall Suzuki rated it at 32bhp @ 7,500rpm, compared to the L/M model's 31bhp at 7,000rpm. So while Suzuki might claim the one-piece head was for better heat dissipation or similar, a 3% increase in BHP is hardly gonna make a massive difference.

I suspect as Dolly said, a 1-piece head is cheaper to cast and machine.

[dollydog]

when i built my gt285 engine, i started with a rebuilt ramair bottom end. i then decided to use gt250a barrels, due to the extra transfer ports. reamed the rear 2 stud holes out and plugged them. then redrilled the stud holes 65mm centre to centre as per the ramair barrels. milled out the transfer ports in the crankcases to match the barrels. had the barrels rebored to 58mm and fitted ts125 pistons on +2mm, then ramair heads and covers. i was explaining all this to a well known tuner who told me i shouldn't have bothered because the extra transfer ports made that little difference as to not matter. oh well, i needed something to do and that seemed like a good idea at the time. apart from the 1bhp gain the gt250a got, i'm sure it also gained weight, which sort of negates the bhp gain somewhat. i still love messing with these engines though - not the 250a. of all the gt250 engines i've rebuilt for myself and other people [a lot], the only ones with crank bearings and big ends absolutely collapsed have been on the later 4 bearing cranks. tells me something
cheers, dd.
p.s. i tell a lie, i did have one ramair engine with a collapsed right side big end. it was off a proddy racer who reckoned he didn't even complete one lap before the fully rebuilt engine 'went'. i bought it off him cheap. the right conrod was bent and the big end was virtually gone. reason? the idiots that had rebuilt the crank had put the right crankpin in the wrong way round. they'd put the crankpin as the 250a goes, so no oil was going to the big end. result, bang, end of race