750 Katana Resurrection

[KiwiAlfa156]

I don't think the head and base gaskets crush that much. I have never had a gasket crush that much on any engine I have rebuilt, car, motorcycle, or aircraft. You could always make a test jig, and using a torque wrench, use a piece of gasket material, replicating a gasket seal, and two equal size flat plates, with the gasket material around the perimeter, then torque them together. I don't think they will crush that much. I knew a guy who rebuilt Rolls Royce engines, they actually use a special thread with a very thin Rolls Royce goop to hold the thread in place, The thread is applied in the middle of the surface contact areas around the perimeter, and cut to meet right at the end. The cases are then torqued together. You are doing a fantastic job on this bike. I have read the whole thread and am quite amazed. That first ride you do will be quite thrilling for you, and rightly so.

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.

[Hayabuser]

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



Keep up the amazing work!

[Suzukian]

Nice thing is, from reading this thread, you're going to document your results, and that is excellent!!

[Nessism]

I don't think the head and base gaskets crush that much. I have never had a gasket crush that much on any engine I have rebuilt, car, motorcycle, or aircraft.

There is a first time for everything...

IMG_1930 by nessism, on Flickr

[Suzukian]

I don't think the head and base gaskets crush that much. I have never had a gasket crush that much on any engine I have rebuilt, car, motorcycle, or aircraft. You could always make a test jig, and using a torque wrench, use a piece of gasket material, replicating a gasket seal, and two equal size flat plates, with the gasket material around the perimeter, then torque them together. I don't think they will crush that much. I knew a guy who rebuilt Rolls Royce engines, they actually use a special thread with a very thin Rolls Royce goop to hold the thread in place, The thread is applied in the middle of the surface contact areas around the perimeter, and cut to meet right at the end. The cases are then torqued together. You are doing a fantastic job on this bike. I have read the whole thread and am quite amazed. That first ride you do will be quite thrilling for you, and rightly so.

[Suzukian]

A labor of love!!! You could glass bead blast the tops of the pistons, then polish with Jewelers Rouge, they would shine like chrome and you would get better air flow. Impressive thread to read. This is one of the few bike that will always be remembered and be a collectible. IMHO

[KiwiAlfa156]

Torqued the head down on the old head gasket and new aftermarket base gasket. Squish clearance measurements were too tight.


There was some variation from cylinder 1 to 4 with 1 being the tightest at 0.65mm (0.025") and 4 being at 0.70mm (0.027") so a 2 thou variation... So it seems that the barrels aren't perfectly parallel to the base. The 2 thou variation is over a distance of about 400mm.... So...

The aftermarket base gasket used to check the squish prior to final assembly measures 0.5mm (0.020) crushed. The old head gasket used to check (which is a MLS type) was 1.1mm (0.043) crushed. I have no idea what the thickness of the original base gasket was, and upon which I took my original squish clearance measurements. The virgin aftermarket head gasket has an uncrushed thickness of 1.3mm. This gasket is made from NI-2098 which has a compression factor of 15-30% at 5000 psi clamping pressure (ASTM F 36).



I have some 0.8mm fibre oil jointing gasket sheet, so proceeded to make a thicker base gasket.



I don't know the compression percentage of fibre but this is usually around the 20% mark. The new head gasket should crush out to +/- 1.0mm so I'll re-torque the head down on the new base gasket and recheck the squish. My target is 0.75mm (0.030).

I'm hoping the sum of the gasket compression will get me close.

[KiwiAlfa156]

Progress. Head painted after new valve stem seals and liquid leak test






Spent half a day scrubbing the pistons. Especially cleaning crap out of the top ring groove. Checked end gaps and fitted the new rings to the pistons.



Pistons back on the rods. Barrels thoroughly cleaned after honing. Barrels back on the crankcase



Next squish clearance check (barrels were planed 0.15mm), fresh head gasket and completion of engine assembly.

[KiwiAlfa156]

Update.

Clutch in.

Valve seats recut



Cylinders honed



And painted



Next, head assembly and valve leak testing

[KiwiAlfa156]

Progress. Had to helicoil one of the front engine mounts. But apart from that all good.

[KiwiAlfa156]

I've been hearing lots of good things about this anaerobic sealer lately. Is it new? I'm gonna have to look into it and put some on the shelf.

I don't know how new it is. Loctite do one as well. It's solvent resistant and is all good temperature range-wise. Blurb says it's ideal for sealing gearboxes. Looks ideal for engine cases.

[slayer61]

I've been hearing lots of good things about this anaerobic sealer lately. Is it new? I'm gonna have to look into it and put some on the shelf.

[KiwiAlfa156]

Finally got some garage time. Time to reassemble the bottom bottom end.


Assembly lube (moly) for the crank bearings.


Shortened an 126 link cam chain down to 122

Upper case loaded. I'm using an anaerobic sealer on the case joint. This stuff stays liquid until its clamped down and starved of oxygen and then it cures between the mating surfaces. Excess is easy to wipe away and internally the engine oil washes uncured sealer away.


I applied it with an artist's brush. It is evenly applied, but the glare from the lights makes it look patchy.


All torqued up. Not too much excess.


Next step is get the crankcase into the chassis (before it gets too heavy) and then clutch, piston, barrels and head.

[KiwiAlfa156]

Will start loading the cases shortly

[KiwiAlfa156]

Some progress while recovering from Covid. The inside of the engine was pretty dirty with firm sludge remaining where the particulates have settled out of the oil as it sat cold for the last 10+ years.




So I spent a couple of days cleaning the cases inside and removing lose paint, oxide and residual dirt.





Reassembled the empty cases, masked up, grease and wax remover, primer grey and the semi-gloss black engine enamel.