Topic: My old Dresda Honda CB500 race head and piston...

[Dresda500]

Good day! I getting my old Dresda prepped for the track after many decades of collecting dust. Pictured is some of the head and piston. I did not build the old motor and don't have much info on it. I'm a newbie on the CB500 so wondered if any of you experts had any idea of what all might have been done back in the day. It was a road racer back in the early 70s at least, not sure how long before it was retired and turned into a street bike with lights. UK shows it was registered as a Dresda in '74. My plan is to concentrate on getting the chassis and brakes in order and run a fairly standard 500 motor this year, but with it's close ratio trans. I found a 650 cam I'll throw in there, it has a old 4-1 that needs a silencer.
So back to the pics....very modified combustion chamber and domed pistons, form memory the previous owner said 12 or 12.5:1..but not sure he knew really.
Valves: shorter and bigger. I guess they had to shorten to get the bigger heads in the modified chamber. Length 3.46inch vs a stock at 3.65in.  32mm dia Int (stock is 27.5) and 28mm Exh(stock is 23mm) diameters. Stem diameter is actaully larger at 6.5mm vs stock at 5.5mm...Valve springs are larger in diameter at almost 29mm.
Straight intake spiggots with 30mm-ish ID.
Ports look pretty good , Intakes are too much polished as was the thought back in the day. I have not put them on the flow bench...they could very well flow less than stock......but probably not.
Piston is a large dome and at about 56.10mm, cast ART in the side. I don't have a stock piston laying around so not sure about compression height, but not much fancy rods back then .
It has a big KH cam, DE grind. It has cam bearing inserts on the lowers, which is the wear side, especially with big cams and springs.

For the 650 cam I'll run this year, are new springs recommended? I know Kibblewhite has some as well as a German manufacturer.
Not sure on what carbs I'll run yet

[Dresda500]

I just put one of the springs on the Rimac and the specs are very clost to the Kibblewhite springs. The Kibblewhite specs are 60# seat and 195# at .440 lift. These old big springs give about 59# on the seat and 210# on the nose.

[Dresda500]

Here's the page from Action Fours sales advert on the DE cam. I like that it gives a stock cam profile and then the DE profile below to compare. I won't be running this until later with a big head and compression. There are likely much better grinds today.

The complete catalog is here if you're interested.

http://www.satanicmechanic.de/download/Action%20Fours%201979.PDF

[bwaller]

Would you let us know the width of the combustion chamber please? The chamber volume has really been increased as the valves have been sunk a lot to allow those sizes. I'm curious about the pistons, CB77 are too large and CB72 too small, but those are crazy tall domes. Someone with experience has done a lot of neat work to get those big valves in there.

I'll bet the bike had long legs but maybe gave up some quickness. The downside to me in sinking the valves so deep the great squish shelf has been eliminated. As a result they made up for it with a really tall dome. As a result it would need long spark lead, probably well over 40 degrees, so would there still be spark 20d ATDC I wonder? The 60's factory racebike piston domes were similar and they certainly worked! LOL 

I really like the cam bearings, wonder where they are from? It would be nice to know the engine history and what power it made.

What sparkplugs were in it, shorter reach by any chance?

Cool as hell Hans.

[Dresda500]

Hi! Yes, I agree a lot of work was put into these. As you said, a bit old school methodology but, a lot of power was made with big domes and still is today(Chrysler Hemi). I wonder has anyone ever dual plugged a CBB500 based motor? Not much room in there, but big dome, or most all 2 valve motors really love dual plugs. I've dual plugged lots of Harleys and KZ1000 loves them as well. On the KZ you can retard the timing about 4 degrees with no loss of power and run much higher CR on pump gas. Eddie Lawson and the 30 or so factory S1 KZ1000 race bikes make good use of dual plugs.

The Chamber is actually slightly oval at 57mm side to side and 59mm across the valves. Depth is 17.5mm from deck to center between the seats. I'll CC the heads and pistons when I get some time and see exactly what CR these come out to.
It would be fun(if I won the lottery and had all the time in the world) to weld up the sides of these chambers and make them into a more modern bathtub design and get some of that squish back...I worked with Traum pistons a bit and they have made custom pistons to my own design before.

I'm not sure what plugs where used, none were in the head. I can dig through some of the boxes of stuff and see if I see anything odd. I was hoping to find a stash of the cam bearings in my parts I got with the bike. Thanks to the internet I found a similar mod on another head in the UK...they are made by Glacier and were originally for an old Villiers 120cc industrial big end con rod bearing, and 7/8" and 0.010 under...or 21.97mm...pretty darn close to the 22mm cam on the Honda... I send Glacier a mail to see if they still have some on the shelf, but not likely...they are in South Africa .

[bwaller]

So probably the CR you mentioned is true. The builder had experience no doubt. I've never seen dual plugs in any of our CB's and I never found a solution. Generally the cam bore is well oiled in a bare head, but I like the bearing.

[MRieck]

 I am curious...what is the valve to valve clearance with the valves on the seats? I'm also curious about intake port flow #'s....I just sent a head to New Zealand and would like to compare the intake #'s.

[Dresda500]

The distance between the valves on the seats is pretty much exactly 4mm. Yeah, I'm curious on the flow as well. I've got a stock head to compare some results to. I'd love to chat offline(or online) about some flow numbers , I guess you have quite the data library on these guys... I've got a small Superflow with D&D blue box.
Id love to find some small beehive springs for these things, I'd think there might be some late model stuff out there that might be an off the shelf item if lucky. For sure when the time comes to run this head different springs and retainers are in order. the rockers are relived a good bit to clear the larger diameter retainers so I'd be thinking about those the entire time at redline.

[Dresda500]

Did some pondering and spec checking and I'd be willing to bet a dollar these are early 69-77 CB750 valves(and springs) that have been shortened to make them fit in the modified head. The early CB750 uses the same 32mm Int and 28mm Exh valve with 6.6mm stem, only 3.935 long compared to my 3.465". That leaves about a half inch to cut back past the original keeper groove and machine the new one. I see Kibblewhite makes a 5mm stem version...but pricey!

[BomberMann650]

I just put one of the springs on the Rimac and the specs are very clost to the Kibblewhite springs. The Kibblewhite specs are 60# seat and 195# at .440 lift. These old big springs give about 59# on the seat and 210# on the nose.

This caught my attention.

If the kibblewhite springs are in the same ballpark as oem.  What makes them superior to the original, and why recommended for big lumpy camshafts?

[MRieck]

I just put one of the springs on the Rimac and the specs are very clost to the Kibblewhite springs. The Kibblewhite specs are 60# seat and 195# at .440 lift. These old big springs give about 59# on the seat and 210# on the nose.

This caught my attention.

If the kibblewhite springs are in the same ballpark as oem.  What makes them superior to the original, and why recommended for big lumpy camshafts?

60lbs on the seat isn't OEM.

[bwaller]

60lbs on the seat isn't OEM.

No probably more like 45-50.

BomberMann650, he was spring testing Kibblewhite against what was in the race head, not stock.

[BomberMann650]

60lbs on the seat isn't OEM.

No probably more like 45-50.

BomberMann650, he was spring testing Kibblewhite against what was in the race head, not stock.

Ahhhhh, thanks for the clarification.

[Dresda500]

As the others said, yes, these are not stock. i found out now that these are CB750 springs shoehorned into the 500 head. I realized in my excitement I forgot to put the retainer on the springs when i tested, so the inner spring wasn't getting full compression, so pressure will be slightly higher.  I'm curious to see the actual seat pressure and then compare the weight of the shortened CB750 valves in the head to a stock CB500 valve. As well If anyone has a stock CB750 intake and exhaust I'd love to get an accurate weight measurement so I can compare to the weight of my shortened valves. Your seat pressure is to keep the assembly of the rocker arm/valve/retainer/keepers in contact...so the rocker doesn't float at high rpm. Valve seal friction can come into play as well, but it's a constant. The lighter your above mentioned assemblies are, the less your seat pressure can be. In my experience it doesn't hurt HP to have a bit too much seat pressure, but for sure HP and valve train damage will occur with too little. The main thing excessive pressure does is wear out components faster. 
It will take me some time to get the head on the flow bench and I apologize for teasing in that matter, but work is super busy and need to mainly concentrate on getting the rest of the bike and motor together as well as all the other guys wanting work done before spring comes.

[BomberMann650]

Shortening a valve spring sounds like an incredibly dangerous alteration that nobody should ever do.🤞🏼😉
Can I try? 😁😁😁

[Dresda500]

Shortening a valve spring sounds like an incredibly dangerous alteration that nobody should ever do.🤞🏼😉
Can I try? 😁😁😁

It might sound dangerous, but its done every day. BUT!!!...you better get the keeper groove dead nuts perfect....all kidding aside,  it actually is very common. You can buy "valve blanks" in various states of completeness from most all the specialty valve manufacturers so that you can machine to your own spec for special projects like this one for example. This head was done in the 70s I assume so not as much off the shelf specialty options, so they used what they had. Today you would run a 5mm or less stem with this valve head diameter and maybe some higher spec material. All out motors tend to drift towards titanium valves and retainers. I like titanium retainers , even on street motors and have been running them since the late 80s in my motors, but titanium valves I tend to shy away from as they are expendable. Depending on the use titanium can last quite long, but you should keep a log of hours and should be replaced as a maintenance item.  I've been building and racing on the salt flats for 20 years or so, so not quite a veteran, but have learned a few things about longevity. We first started iwith titanium in our motors, both intake and exh, but soon learned that going 5 miles at WOT at 10,000rpm for an entire week at Bonneville Speedweek was not conducive to a happy Ti exh valve and proceded to spit the valve head out the exhaust and we never found the part....We now use extensively Inconel valves, which are heavier, but never lost another valve as they handle the heat better. I tend to look at Bonneville like a lonely endurance race so take lessons learned there to road racing where you will have the possibility of extended periods of high rpm and heat, compared to a street or drag motor. When I was a broke college kid and trying to go fast on the weekends I would buy used Ti valves from the Nascar guys or get them for free as their "lifetime" had expired...but looked new...So I ran MANY a thousands of miles of old race valves in my street car with some added stem clearance for peace of mind. Never lost a valve, but won many a race that helped but me through engineering school. Gotta do whatcha gotta do!
On a side note, shortening a stock valve you need to think about that if there was a hardening process to the tip for wear purposes, you should either get it re-hardened(scary or guesswork as you don't really know what material it's made from, but I have done it many times in my home shop with DIY case hardening compounds like Casenit)...or run lash caps and keep an eye on your machined keeper grooves during teardown to make sure they aren't "moving"...

[simon#42]

from memory the bearing conversion used to be done in the uk by joy engineering , it was quite a common mod. not for any performance enhancement just to save a damaged head .

[MRieck]

Shortening a valve spring sounds like an incredibly dangerous alteration that nobody should ever do.🤞🏼😉
Can I try? 😁😁😁

 ...or run lash caps and keep an eye on your machined keeper grooves during teardown to make sure they aren't "moving"...

I am a big fan of lash caps and think that is the best solution....very easy to replace a lash capwhen they wear.

[simon#42]

not so easy to find them when they get spat out though . fine for a road bike if you are sensible but i would avoid them in a racing engine . if you over rev and get valve bounce they can dislodge . this happened on my sohc road bike while being stupid .

[Dresda500]

Shortening a valve spring sounds like an incredibly dangerous alteration that nobody should ever do.🤞🏼😉
Can I try? 😁😁😁

 ...or run lash caps and keep an eye on your machined keeper grooves during teardown to make sure they aren't "moving"...

I am a big fan of lash caps and think that is the best solution....very easy to replace a lash capwhen they wear.

100% agree, much easier/cheaper to replace a lash cap and rocker at the track if something goes wrong and as well just in general, grinding on your valve tips every winter, eventually new valves will be in order. I don't have enough experience with these motors to know if the stem wears out before that would be an issue. Mike, are most guys using the Kibblewhite valvetrain parts or are there other options off the shelf?

[turboguzzi]

hi dresda, nice to see pics! first thing that comes through my mind is to check the pistons.... in the two pictures where they are upside down there seems to be a clear crack mark in the rings area, hope it is not what it looks.

like brent said, not clear if these tall domes create any squish, would do a quick dry build, put little plasticine blobs and measure what the squish thickness between dome and chamber wall is... if its above 1mm not much squish to help you fight detonation

people back then got away with this chamber config with very high octane fuel, indeed like old school hemi's they are very prone to detonation.  if you can run and find 100 octane, go for it!

cant se the point in dual plugs in a 56mm bore, and almost certian it is not doable with our sohc in the middle. Muzzy did dual plugs in his big KZ and Gpz750, but there is a lot more room there with their dohc configuration.

[Dresda500]

hi dresda, nice to see pics! first thing that comes through my mind is to check the pistons.... in the two pictures where they are upside down there seems to be a clear crack mark in the rings area, hope it is not what it looks.

like brent said, not clear if these tall domes create any squish, would do a quick dry build, put little plasticine blobs and measure what the squish thickness between dome and chamber wall is... if its above 1mm not much squish to help you fight detonation

people back then got away with this chamber config with very high octane fuel, indeed like old school hemi's they are very prone to detonation.  if you can run and find 100 octane, go for it!

cant se the point in dual plugs in a 56mm bore, and almost certian it is not doable with our sohc in the middle. Muzzy did dual plugs in his big KZ and Gpz750, but there is a lot more room there with their dohc configuration.

HI! Yes, I totally agree, a dry build and some clay to check clearances is in order. I suspect there is not optimal squich on the setup, but the the sides of the done are quite close to the chamber wall by eye, but that's just setting the piston in there so no idea of piston height in real life. I can tell these chambers are hand formed so will have some differences from chamber to chamber, also not optimal, but we will see. I have an extra motor that is torn down that I could throw crank and rods in and as well have the cylinder that is the match to these pistons so it's an easy check  when i find the time. Controlling detonation will be key as me being in Norway, the 98 fuel we get at the pump isn't really 98 in my experience and honestly this bike is not competitive against the TZ350 which we must run against, so it's just to go out and have some fun with friends in the classic racing arena. But of course I don't want to be the last guy across the finishing line while they are trying to close the track... Luckily I do all the machine work and welding/fab in my own home shop so it's mainly my time and of course a handfull of dineros.
I agree, I don't think the dual plugs is worth the effort and man it's not much space in there. I machined dual plugs for my Moto Martin Chassis KZ1000 and the bore size on those LOVE it.  I'm just looking at the dome height VS diameter and it sure couldn't hurt on this particular piston and chamber, but likely not worth it.

[Dresda500]

from memory the bearing conversion used to be done in the uk by joy engineering , it was quite a common mod. not for any performance enhancement just to save a damaged head .

Thanks for that Simon. I also heard there was a Dixon Engineering or Dixon racing that did this stuff back then as well? I tried googling the name but just come up with a modern race team

[simon#42]

dixon racing used to be the yoshimura importer back in the late 70s early 80s  i think they also sold bimota  frame kits in the days before bimota made bikes . i went there a couple of times but dont remember them doing any machining work . joy engineering are still going it might be worth emailing them and seeing if anyone is old enough to remember !

[MRieck]

Shortening a valve spring sounds like an incredibly dangerous alteration that nobody should ever do.🤞🏼😉
Can I try? 😁😁😁

 ...or run lash caps and keep an eye on your machined keeper grooves during teardown to make sure they aren't "moving"...

I am a big fan of lash caps and think that is the best solution....very easy to replace a lash capwhen they wear.

100% agree, much easier/cheaper to replace a lash cap and rocker at the track if something goes wrong and as well just in general, grinding on your valve tips every winter, eventually new valves will be in order. I don't have enough experience with these motors to know if the stem wears out before that would be an issue. Mike, are most guys using the Kibblewhite valvetrain parts or are there other options off the shelf?

Yes.....Kibblewhite is a big supplier of bike valve train parts.