cutting gt 550 head into 3

[platesnscrews]

i 'am thinking of cutting my gt 550 heads into three pieces good idea or bad. were do i cut them? any pictures would be a great help.

thanking everybody in advance

[Craig380]

I did this a few months back on my 380, in the hope of fixing a recurring weep from the centre cylinder head gasket. With the head in one piece, the two rear studs on the centre cylinder gradually 'fretted' loose. Having to retorque every 1000 miles or so eventually destroyed the alloy threads in the jug (a combination of old age, vibration and heat cycles).

I had the stud holes helicoiled, and cut the head into 3 pieces. After 500 fast miles, all head nuts are holding torque with no loosening at all - and no weeping.

See the pics in this thread of a 380 head - either side of the centre combustion chamber there is a long fin that runs from the front to the back of the head (it's the fin that is not joined to the others by metal). Make your cuts OUTSIDE that fin, so the new "middle" cylinder head has both of those long fins. That makes sure the middle head has plenty of cooling fin area to dissipate heat.

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[platesnscrews]

thank you for that information

[Alan H]

Why cut the head anyway? Is one of the head gaskets leaking and won't seal?

[Suzsmokeyallan]

Alan even the X7 had that problem with the one piece head and eight bolts. The 380 and 550 with bigger one piece heads suffer from constantly leaking head gaskets due to the stresses of the separate cylinders acting on its mating surface.

[Alan H]

Well I never had problems with the original J back between 1972 and 1976 or so, and I don't remember anyone else having problems back then, so we'll have to see how this K goes, then the A which will be next to feel the gentle caress of Mr. Hammer later this summer.

[Lorenzo]

I was wandering if, having the heads o-ringed would be of any help

[Craig380]

Well I never had problems with the original J back between 1972 and 1976 or so, and I don't remember anyone else having problems back then, so we'll have to see how this K goes, then the A which will be next to feel the gentle caress of Mr. Hammer later this summer.

The problem I had was fatigued threads in the cylinders - 30+ years of heat, vibration etc of the steel studs in the alloy barrels meant that the two rear studs on the centre cylinder eventually stripped the threads in the barrel.

As well as getting helicoil repairs done, I reckoned cutting the head into three was worth trying, to reduce the 'fretting' effect.

[Alan H]

I see where you're coming from now. I couldn't see how the head could warp and leak, but if studs were less than good, then problems obviously can occur. A point to note for future.
I've had to helicoil a couple of things on the 550 that I've almost finished, but the head studs appeared OK. We shall see!
Where's the 'fingers crossed' smiley when you need one?

[yeadon_m]

I am wondering if the separate cylinders / one head part is the issue. On the GT750, the cylinder is a single block so as long as its flat and so is the head, it should seal.
With the 380 and 550, we're assuming that the height of each cylinder is precisely the same when mounted on the crankcase, so that the one piece head will lie perfectly flush to the top (so long as its not warped!).
If they are in fact not perfectly the same height, eg just manufacturing variation, some bikes might see head leaks and others not. I have not on 4 aircooled triples, but I know quite a few have had problems that recur.
Just a thought.
I've no idea beyond using eyes and a good straight edge how to invalidate or prove this idea.
Cheers,
Mike

[Suzsmokeyallan]

Being an aircooled engine the rates of expansion and contraction change through out the heads and cylinders quite differently that those on a liquid cooled engine.
The GT750 cylinder and head is each a heavy one piece casting that never sees the stresses the 380 and 550 ones do, neither in constant higher rpms or intense heat generated by such.
The inner cylinder on the 380 and 550 runs at different temperature than the two outers mainly due to less airflow around it and a reduction of cooling fins on both sides of that cylinder. Suzuki tried to address this cylinders problem with slightly different jetting for the middle cylinder in an attempt to reduce the temperature of it.

Having that large finned but rather thin head bolted to three separate cylinders that are constantly trying to flex it during their heating and cooling cycles means something has to give. In most cases the middle cylinders head studs torque setting are usually what gives first, and you will constantly find yourself retorquing them after 1000 miles or thereabouts.
Cutting the heads apart allows each cylinder and head to become its own individual unit to expand and contract as one piece without the stress of an adjacent part being attached to it.
Cut them apart, check and true all the mating surfaces, fit new gaskets, torque the heads and cylinders to spec and you will find the leaking issue will resolve itself.

One case in point, a 550 owner who had that same problem for years, got fed up and simply began using the bike less. One conversation we had about the bike and he confirmed the middle cylinder head gasket always leaked and his ritual of constantly torquing it and the others over and over as the miles go on.
We talked about cutting the head apart and the virtues of doing so,which he did a few weeks later and fitted new head gaskets. That was over three years ago and hes had no further issues since then.
Back in the day when these bikes were new the gasolene had lead in it, that alone changed the running temperatures of these engines and it would obviously have made a difference then.

Its not like theres no return, if you don't want to cut your head apart, then get a head off of Ebay or a wreckers yard, cut it apart, clean it up and try it.

[dyrberg123]

Hi Guys,

Just stumbled over this thread. I had a GT380 2 or 3 years ago, always going loose on the two middle back studs, ore blowing a middle gasket when i rode it hard, or as hard as you can on a GT380. I cut the head in three pices, left the two finns in each middel to benefit the middle head piece, HOPE THAT MAKES SENCE for best cooling there.

After this light operation i had the now three piece head skimmed as lightly as possible 0,2mm i seems to remember, and never had any problems after that.

Cheers

[Craig380]

Having that large finned but rather thin head bolted to three separate cylinders that are constantly trying to flex it during their heating and cooling cycles means something has to give. In most cases the middle cylinders head studs torque setting are usually what gives first, and you will constantly find yourself retorquing them after 1000 miles or thereabouts.

That was exactly my situation. After rebuilding the top end, a check of the head studs after 50 and 500 miles showed the rear nuts on the centre cylinder needed torquing back up to spec ... all the other nuts were fine and stayed at the recommended torque. Those same two nuts were loose again after every 1000 miles.

Then last summer, one of the nuts just kept turning instead of taking the torque 30+ years of heat cycles and the frequent retorquing had fatigued the threads in the cylinder (the head studs being steel doesn't help either).

I checked the head nuts last week, 500 miles after cutting the head into 3 pieces. All rock solid.