Harsh Reality Pics - The Black Museum

Laverda SF

Hero member
Geez! Greg shimming gear caskets would seem to me a waste of time and expense if all you to do is use thicker Barrel with a Head gasket - Any combination there of ?

Just about any Gasket Co. today can punch you out a solid copper or compound barrel or head gasket to your specs for a reasonable price.

Mr Gasket, ISKY, Elelbrock, Manley, Wiseco... etc. That's what them Company specialize in.

I would shy away from modifying original cam stanchions and gear geometry.

I've no clue why he had to mill engines surfaces but guess he had his reasons.
 
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piranha-bro2

Hero member
Location
Melbourne
Ron, your thinking is about half a century too far into history - NO separate barrel (like a car block), and a gear driven cam system doesn't use 'gaskets' to obtain a workable clearance. The reason they have to be shimmed is that the cam gears in the heads are now closer to the driving gears on the top case ('barrel', to use the incorrect term) because the heads have been shaved.

If I'm wrong, happy to be thrown to the wolves!
 

Laverda SF

Hero member
I believe one of the worst things you can do is over mill the head to increase compression as it causes complications with the valve train.

Just replace the piston with a higher a dome with deep valve reliefs.
Leave the Valve train concentric alone.

I've no excuse for using big dia and light valve with with a smaller valve guide and heavy valves springs using an original Breganze cam.

Of course I'm referring to the 1970 Breganzie 750 SOHC - If that makes a difference.

At least I got to 7800+ RPM approaching 8000 before I shifted. Using Dellorto 30A's open mouth VHB's on a Breganzie Twin.
 
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GregT

Hero member
Location
Hororata NZ
Thicker gaskets is a good idea Ron, except it would be a shame to bugger up all the work done to increase compression 🤔😘
If only it had been done to increase compression.....It's had a leg out of bed in the past - and been very nicely welded back up.
But after relinering, they've decked the barrel tops approx .015in each. I say approx because that's what's etched into the cases - but it measures up as a bit more than that.
At this point in it's history all concerned with it just want to see it run reasonably well - at least once anyway.
Nominally it's wanted for next Philip Is. If it goes ahead - and if all the bits come back in time.

Ron - google Honda RC30 and you'll see what I'm talking about. A 16 valve V4 with four gear driven cams
No expense spared when they built them. Now selling for small fortunes.
 

Laverda SF

Hero member
Let me repeat: "I believe one of the worst things you can do is over mill the head to increase compression as it causes complications with the valve train."
 

Laverda SF

Hero member
Chrisk, I recommend just minimal shaving the head to make it flat - to rid warping NOT for the purpose of increasing compression as it will case issues with the Valve train geometry.

Buy a piston with a higher dome with deep valve reliefs. Use a bigger dia lighter valve with smaller stem dia and suitable valve guides, do your Valve job, use Heavier Valve springs with lighter retainers - Choose a Cam to meet your criteria then jet your carburetors accordant. By all means do a little porting especially directly beneath the valve seats in to the bowl.

No need to shave your heads unless minimally just to straighten a warped head without upsetting valve geometry.

Head and Barrel Gaskets are available in any thickness.

Keep your engine casing perimeters to manufactures specs.

Guaranteed a Hi-Revving long lasting Breganzie - a SFO in my case but not to say the same for any Motorcycle or Car Engine.


.
 
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Laverda SF

Hero member
Talking about taking a piss: An oversized valve allows more seat material for the machinist to work with to keep that valve seat as high as possible but also more flow at low lifts.

I never did loose a race with my 70 750 SFO except I had to concede to my Buddy riding an 81 Harley Wide Glide mainly because he would not give up riding in a torrential down pour and I was sliding all over the place after some 200 miles in the middle of the night and he beat me to death ;o)|

Chrisk a 2 Stroke 2 Cyl Kawaski Invader 440 mill in a John Deer Sport Fire Snowmobile now your talking - Not even an Arctic Cat 700 could even come close. (Snow Sleds). I was running dual 38 Mic's with either a dual or a big single expansion chamber - Actually the single expansion chamber was better over all.

Where is that machine now - Our youngsters don't have clue how FAST She is !
Of course I had my gas mix for her: 110 octane (Sunoco 220), lots of Alcohol and Red Ex.
She not very good concerning fuel mileage. Actually she stank of fuel stand off ;o)
 
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GregT

Hero member
Location
Hororata NZ
Just replace the piston with a higher a dome with deep valve reliefs.
No - just simply, No. Where you're working with a deep hemispherical combustion chamber the aim is to make the space for the compressed
mixture as compact as possible. A high dome in this type of chamber gives a very poor shape - and needs a lot of spark advance.

The 74mm bore 350 Aermacchis with a deep hemi chamber typically run 36 -38 degrees advance with high dome pistons.

The flat-top piston in the pic is a shape we came up with after a lot of trials. 11.8 : 1 compression - and 28degrees advance on 100 octane.
It matches the sides of the chamber closely and concentrates the volume around the plug.
 

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BobSol

Junior member
Location
Coventry UK
Hi Greg
Nice to be right for a change. I've had a fair bit to do with RC30's over the years and feel your pain. Genuine parts are very difficult to source now but Honda have just announced that they intend to reproduce all the obsolete parts. The access holes in the cam carriers for the head bolts can be opened up so more substantial hex drivers can be used for more reliable head torqueing. The adjusting shims were available as a race kit HRC part. Very difficult to check gear cassette to crank gear clearance but provided you can still feel crankshaft end float with thumb pressure you should be good. A fabulous piece of engineering which with careful assembly and the right parts gave huge power increases. Probably the last bike you could buy and have a chance of winning on.
Enjoy Bob
 
I only rebuilt a couple of RC30’s - one was a warranty job and I think it was rods and valves and the other was a track day bike. One of those perfect motorcycles.
I won’t mention names but a certain TT riding visor manafacture from the Midlands bought two new RC30’s one for him to race and one for his son registered for the road- the motors were swapped and the race bike then had an engine that was covered by the warranty. Honda knew what had been done but honoured the warranty, had a few cranks from memory!
 

GregT

Hero member
Location
Hororata NZ
I admit I was surprised when i looked at the crank in this one. I've seen quite a few V4 Honda cranks - from 400's to 1000's - and it's just the same as usual - poorly finished. It dates from the period when they thought simply running a linisher over the oil holes on the crank surface was enough finishing. The first thing I do now on the V4 cranks is radius the oil holes properly. Makes a world of difference to the crank life.
 

sfc1000uk

Hero member
I admit I was surprised when i looked at the crank in this one. I've seen quite a few V4 Honda cranks - from 400's to 1000's - and it's just the same as usual - poorly finished. It dates from the period when they thought simply running a linisher over the oil holes on the crank surface was enough finishing. The first thing I do now on the V4 cranks is radius the oil holes properly. Makes a world of difference to the crank life.

that surprises me that they hadn't made more of an effort with the RC30 cranks - not that the poor finishing let the vanilla RC24 cranks down, not in road use anyway - I know of a couple coming up for 250k miles, my highest mileage one had 97k on it when I broke the thing, engine was still sweet but the chassis & bodywork were so thoroughly bodged it was simpler (& cheaper) buying another RC24, barely run in at 60k miles :)

I seem to recall that some tuners upped the compression (again, RC24 instead of RC30) by building up weld on the piston crown and then maching it.
 

CLEMTOG

Hero member
build up pistons with weld and machine? bloody hell that needs care and skill to achieve, but I once came accros a bloke in a workshop that had made a jig so that he could "stretch" Honda 400/4 conrods by about 3mm, this was because he was using pistons from something else that did not have enough height, he welded up 14 of them, 2, were ourely for practice and set up, 12 were for the production, then destruction tested four of them (multiple reverse bending, hydraulic compression and stretching) and all was good, so he built his two engines with the other eight, they were about 650cc I think, bores may not have been stock either, I am fairly sure the crank was stock, never heard of them breaking and he used both for many many years, this is the sort of thing you do if you are extremeley careful, clever an ex sidecar race champion and are vertically challenged, he wasnt even five foot.
CLEM
 
Back to the original theme. Left the fuel taps on with resultant hydraulic lock. Put back in shed with fuel taps still on. At next start attempt was seized. Flat broke student so left until I had enough loot to fix it.

Cranky.jpg
 

GregT

Hero member
Location
Hororata NZ
Back to the original theme. Left the fuel taps on with resultant hydraulic lock. Put back in shed with fuel taps still on. At next start attempt was seized. Flat broke student so left until I had enough loot to fix it.
Ouch....Back in the day, I saw an awful lot of Suzuki T500 cranks just like that. Vacuum taps that leaked - and a good strong kickstart assembly.

Clem - The Britten Titanium rods were cut and welded to suit from an off the shelf rod that was too long. A guy on the staff of the rod manufacturers did the job in his home workshop. To my knowledge, none have let go - yet.
John apparently balked at the costs of his own rod with the associated costs of dedicated CNC programmes.
 

Dellortoman

Hero member
Back to the original theme. Left the fuel taps on with resultant hydraulic lock. Put back in shed with fuel taps still on. At next start attempt was seized. Flat broke student so left until I had enough loot to fix it.
What was the problem with the crank Davo? Only thing I can see is rust, and maybe some stiffness in the big-end bearings (rods are all standing up rather than lying against the case).
 
What was the problem with the crank Davo? Only thing I can see is rust, and maybe some stiffness in the big-end bearings (rods are all standing up rather than lying against the case).
After a hard drive self destruct I have lost the emails from Red, but from memory all bearings were rock solid and the big ends of the rods also rubber ducked. Ended up looking like this
crank (assembled)2.jpg
 
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