750 Katana Resurrection

[Big Block]

Super interesting tutorial. Thanks for posting your progress.

[Suzukian]

That gasket looks great! They are a PIA to make, but well worth the effort. Great outcome your taking time paid off. I wouldn't use it on a Top Cover gasket, but on other gaskets that aren't coming apart, or to seal cases, Yamabond#4 is incredible. I used it on my M.G Midget (1973) as the stock oil pa gasket would always leak. I had to remove the oil pan, and the gasket came apart, split in halves right down the center. I brushed a little Yamabond#4 on the halves, put it back together, hasn't leaked in 8000 miles. A little scary because if your British car doesn't leak oil, you have to make sure there's oil in it.

[KiwiAlfa156]

Yes, having replaced the ATU drive dowel with a section of shank from an appropriate diameter drill bit, I thought it wise to index the timing marks.

Pulled out the cam cover gasket and it was the earlier bolt pattern... Poos!

So I have gasket paper and time on my hands, and I don't want to wait for a gasket to turn up.



I used the cover for the basic outline and assembled the pieces of the old gasket and the wrong gasket to get an detailed outline and internal pattern. Bolts were placed punch punched in the gasket and aligned with the cover



The finished article. The gasket sheet was 10mm too narrow, so I distorted one of long sides into a shallow vee, thinking that there's enough flex for it to sit flat when pulled into position. It worked. Well pleased. Only took 2 and a half hours.

[Suzukian]

Great to see someone doing this kind of work with the care it deserves.

[KiwiAlfa156]

Camshafts in and valve clearance set


Indexed TDC with a dial gauge, and the reference mark was out, so made a new mark to indicate true TDC

[KiwiAlfa156]

The results of the journey into the squish zone ended up being a bit of a mixed bag. They clearance in all cylinders are closer to what I was aiming for, but not exactly there. What I have learnt, is that gasket compression is much less that what I expected due to the comparatively low stud/nut torques and thus clamping forces applied to the gasket. There is significant thickness differences between brands of gasket, and that finding appropriate base gasket or material to cut base gaskets of the various thicknesses to adjust squish clearance is difficult because you are wanting to make adjustments in the 100th of a mm.

So in the case of this build, the squish clearance has a variation from cylinder 1 through to 4 of 0.05mm. With the tightest clearance (cylinder1) being 0.82 mm and the widest at cylinder 4 being 0.87 mm. I was aiming for 0.75 - 0.80 mm.

So why the variation?

A couple of options: the barrels may not have been planed perfectly square, or there is some distortion from the PO running the engine with a broken stud and ridiculously high torque on the remaining cylinder studs. So if it had been planed with reference to the head/barrel mating face, which is highly probably, then any variation in the deck height of alloy barrels wouldn't be machined out. What ever the reason, it is what it is. And in a road bike, I don't think it will make a huge difference. Having received it as a non-runner, I have no previous data or experience to compare it with.

Will it improve performance?

Skimming the head and taking 0.15mm off the barrels will have a positive effect on compression ratio. Re-torquing after a few heat cycles may also nip up the squish clearance a nanometer or two. Looking forward to running her, and that isn't too far away.

[KiwiAlfa156]

OK, next update. Had to do some repairs. The first road block was swapping camshaft sprockets to my good spare inlet. Apparently there was a camshaft material change in later GS/GSX with a higher bolt torque.... This I didn't know and used the figures from a later torque table and... Bugger... Cracked both bolt holes on the cam. A bit of ringing around and found a specialist machine part welder. They work with cast materials and did a fantastic job.



Next repair was also welding, this time by me building up the drive lugs on the ATU that got sheared off. MIG-ed up suitably sized beads and then ground and filed to shape



Now I can rotate the crank the normal way rather than by using the rotor bolt. So stator/cover back on. Have put in the oil filter, neutral switch, and the final drive sprocket. Just the camshafts to fit, valve lash, ignition timing, pipes, carbs and airbox to be fitted.




Last piece of the puzzle will be a new Rec/Reg. After finding the rec/reg to be the cause of a vicious parasitic drain on the battery in my 650, I tested the part fitted to the 750 with less than stellar results. So a replacement has been ordered.

[Suzukian]

It's cheap insurance, and a lot of factory manuals don't mention it, but it should be done. However, you haven't touched them so you're good to go. I shot peened the Rods on the last bike engine I built, so I purchased new nuts and bolts to not have to worry about it.

[Nessism]

The factory manual makes no reference to changing rod bolts. I'd leave well enough alone, unless you plan to race the bike.

[KiwiAlfa156]

Just a quick question about the connecting Rods. Another forum I was on had the guy rebuild the motor, and he reused the connecting rod bolts. Those bolts for the most part are a torque to spec, then leave it. They cannot be used again. He ended having a rod come through his crank case. Fortunately, he had another motor, but lost a lot of work on the over bore, and everything he did to this motor.

I don't know what you are planning with your connecting rods, but find out if they are of the "single use' variety. Personally, I always put in new bolts on connecting rods. Bolts lose approximately 70% of their strength when over torqued. The single use bolts are essentially over torqued by a much higher factor, as they initial torquing brings them to their max strength, and they do not "un-torque" when loosened, they stay stretched. I would hate to see you lose your superbly detailed engine for the price of new connecting rod bolts. A new set would be money well spent. IMHO.

I agree that fresh rod bolts are cheap insurance. I ran the engine prior to beginning work on it,

And as the crank/conrod clearances/play were all well within spec, I elected not to disassemble the conrods.

[Suzukian]

Just a quick question about the connecting Rods. Another forum I was on had the guy rebuild the motor, and he reused the connecting rod bolts. Those bolts for the most part are a torque to spec, then leave it. They cannot be used again. He ended having a rod come through his crank case. Fortunately, he had another motor, but lost a lot of work on the over bore, and everything he did to this motor.

I don't know what you are planning with your connecting rods, but find out if they are of the "single use' variety. Personally, I always put in new bolts on connecting rods. Bolts lose approximately 70% of their strength when over torqued. The single use bolts are essentially over torqued by a much higher factor, as they initial torquing brings them to their max strength, and they do not "un-torque" when loosened, they stay stretched. I would hate to see you lose your superbly detailed engine for the price of new connecting rod bolts. A new set would be money well spent. IMHO.

[93Bandit]

Thanks Suzukian. I beginning to think the crush will be minimal too (at least as a dry/cold install for measurement). Both base gaskets (aftermarket and hand-cut) have been measured before and after being torqued down and show no permanent change... That being said there should be 'recovery' from the crush, but should it be 100%?. The standard test for gasket materials concerning deformation ASTM F 36, gives a percentage of thickness lost at 5000 psi and the percentage recovered after the pressure is released. The problem is that you can't really calculate the pressure on the gasket directly from the torque applied to the studs, or whether it's anywhere near 5000 psi....

The test you propose would provide the answers but I think from the clearance measurements I've already taken, the crush on the fibre head gasket won't be of the magnitude that is going to cause problems.

I found an interesting post on a Porsche forum, about cylinder head nut torque values for early air-cooled 2.7 911 engines (alloy cylinders, steel liners, alloy heads and steel studs) and the issues caused due to heat cycling and the differential coefficient of expansion between the steel studs and alloy barrels. Apparently it was a problem and Porsche came up with studs made from a special steel alloy called Dilivar which expanded at a rate closer to alloy bits, to combat studs pulling out and barrel distortion.

The reason I mention all this is that under heating the the tension on the studs is increased due to the alloy barrel/steel stud combination as is the clamping force at the gasket faces. According to the Porsche site, re-torquing the head nuts at the first service was to take up any 'slack' in the head gasket due to crush caused by alloy expansion from the post-assembly heating/cooling cycles. I suspect this is required on air cooled motorcycle engines too, as they are essentially the same construction.

The post also talked about how stud tension on the air-cooled engines were set well below peak head bolt tension in modern water-cooled auto engines. These are often clamped using using torque to yield bolts to maximize clamping force. Air-cooled studs screwed into the crankcase act more like springs, which is handy given the expansion rates

I'll be going with the aftermarket 0.5 mm base and the 1.3 mm fibre gasket which will give about 0.75 - 0.8mm squish which should be safe. But I will measure to be sure.

I am looking forward to riding it. It's spring down here at the bottom of the South Pacific, so some summer riding is in order.

The Suzuki service manual includes head nut tightening in the regular maintenance schedule.

[KiwiAlfa156]

I have a soft spot for orange Kats after owning the Wilton 1260 for three years.

Keep up the amazing work!

I always wanted to do her in orange pearl' -Tiger Mica - a Holden (GM Australia) colour. It was going to be solid, and it was actually pics of the Wilton 1260 that inspired me to add the Black Pearl

[slayer61]

Kaz Yoshima CB400f

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[Suzukian]

When Kaz Yoshima helped my on my CB400F build (Stage III 458 cc kit), it was a completely different bike, but no matter what I did, I could not get rid of the weeping of the Honda Cylinder head weeping. It wasn't leaking, it just wept. I just carried a rag, and would wipe it ever 500 miles or so. Much older technology. It never blew. The motor has 8K miles on it, ad last time I started it before setting it up with storage, it ran fine. The bike, which a much smaller and thinner me, was clocked at 135 mpg. It took a while to get there, but that was screaming at 14,5000 rpm's, and it was a burst. It could do 120 all day long. I think you'll have much better results. I was going to use Yamabond #4, but if it didn't work, the clean up is time consuming. That stuff is fantastic though, and it sealed the cases. No oil, of even a hint that there's oil in there.

The care you put into this is admirable, and the documentation is excellent. I have a forum of 50K model builders, mostly paper, but really anything you want to use, and I know a quality, well thought out thread when I read one.