Nice start on the project!

 

I think the French have a similar word too

 

This is going to be awesome. Good luck in your venture!

 

Armand,
I don't think your comments are especially funny so please stop cursing in my project topic. Go do something constructive instead.

Captb and 74cb360t,
Thank you for your kind words!

 

Armand,
I don't think your comments are especially funny so please stop cursing......

:-o Certainly I will!

 

First of all, since the last two pages in this topic contains a lot of playing with word and also some foul language is it OK with you guys if I clean it up a bit?
I think this will make it easier to read when the project picks up speed in a couple of months.

I'm now starting a serious search after a CB500T engine in reasonable condition. They doesn't seam to be very easy to find in Sweden (or Europe) though but I really hope I will find one before fall.

 

Clean it up Ronny

 

Ronny, Please clean it up, this is about motor cycles!

 

I've spent the fall searching for a 500T engine unfortunately without any luck but last week I found a complete CB500T (in parts) so the project can finally proceed in my newly finished workshop.

The bike might look ok in the photo but it's too far gone to save. I will be able to use some parts on the Bomber build but all chrome parts have a lot of rust.

The engine has overheated and the left piston has nipped up resulting in broken rings and scores in the bore. The engine will probably need a full top end rebuild but the crankshaft and gearbox seam to be ok.

 

Nice to see you have a 500 engine. What are your ideas for pistons?

 

Yes - now you have a longer stroke engine, will you take it out to 73mm or 74mm in bore to square it up again?

 

Hi Ronny,

Good to see you back,

Jensen

 

I've thought about Kawasaki KZ1100 1.5mm over (74mm) pistons and the THR 74mm forged pistons. I have some questions to THR first but I'll probably go with their kit.

 

Wiseco has a Z1100 1.5mm forged piston. The critical item will be the location of the wrist pin bore in relation to the piston crown. I think it takes it out to a 74mm bore. I spoke to them when I was putting my 450 together. My rod small end was over tolerance for the diameter. They had a machine shop that could grind a 18mm wrist pin to any size I wanted. I would think they could put the wrist pin hole any where you want it.

http://www.wiseco.com/ProductDetail.aspx?ItemID=4256M07400&ModelID=175&ModelYear=1981&AppID=7901

 

Jim. as I understand the (stock) Z1100 piston must be slightly modified at the edge of the piston crown and also at the valve outtakes so THR's kit seam to be the easier route. THR's 450 pistons will sit about 2 mm under the top of the cylinder wall in a 500T engine hence making the compression slightly lower than on a 450. This will suit my project well as I'm more after low and mid range torque than a lot of HP at high revs. I might also try an intake cam with a little longer duration and avoid higher lift as I think it's not a good idea to put even more strain on the cam followers.

 

Ronny, I have been thinking a lot about doing what you are starting. But I need to finish my 450 K5 and I have a '81 GL1100 Standard that needs to be done first. I had a conversation with JayinNY on a similar proposal last November. My comments are applicable here. The difference is you will have a larger displacement engine. That will shift the calculation slightly to a higher compression engine. I apologize if you have already read this:

The dimension from the wrist pin bore ont the 500 engine to the top of the piston is shorter than on a 450. it is exactly 1/2 the difference between the 450 and 500 stroke. The CB450 stroke is 64.8 and the 500 is 67.8. the difference is 3mm so the wrist pin is 1.5mm (~.060) closer to the crown. This would affect the squish band and compression ratio.

The new compression ratio could be calculated by using the formula for a volume of a cylinder; Volume Calculator = 5775 Cubic MM or 5.77 CC. since a stock 450 is 444 CC, each cylinder is 222 CC, at a 9 to 1 compression ratio, the stock 450 DOHC combustion chamber volume is about 25 CC. Adding another 5.8 cc would make the compression ratio about 7.3 to 1.

To deal with using 450 pistons in a 500 the height of the cylinder block could be shaved by 1.5 mm. this would allow the stock compression ratio to be maintained, the piston crown would need to be shaped to match the 450 head. Another compromise would be the cam timing. Since the cam centerlines are 1.5 mm closer to the crank centerlines, the tensioner will need to take up the difference. I'm sure it could, but it would push the whole chain length difference to the back (or slack side) or the rotation. This would advance the cam timing off by 1.5 mm rotation of the (calculate: cosine of 1.5mm at the radius of the cam) cam chain sprocket. I've had enough math for one posting but it would be around 3-4 degrees.

Of course your situation is a little different. A 7.5 to 1 compression ratio would be easy to live with, but I think it would feel like a tired engine that is down on compression. I'm watching with very high interest. JimP

 

Jim, the THR forged pistons are high compression (11.5:1) 450 racing pistons so the end result on a 500T without shaving the head or cylinders will probably still be higher compression than a stock 450. Since I'm not shaving the head or cylinders the cam chain, and thereby the cam timing, will not be altered from stock specifications.

 

What bore size will you wind up with? I will calculate the compression ratio.

 

74mm.

 

I discovered a couple of errors in my thinking. I hate it when that happens, especially in an international public forum.

I used the incorrect stroke for the 450 in the example above. Also, I am postulating the is wrist pin hole in the CB500T is closer to the crown of the piston than in the CB450 and the length of the connecting rod is the same between the two engines. My error was thinking the 450 pistons would have a lower deck height in the 500 than the standard pistons. Based on my assumptions, the opposite is true.

The difference in the stroke is 7mm. If Honda made up for the difference by making the piston shorter, in the 450 piston, the wrist pin bore would be 3.5mm closer to the crown than in the 500. I have a set of old 450 piston out of a K6 motor. Using a caliper I measure the center of the pin bore to the top edge of the squish band area at 25mm. The squish are of the crown slopes about 1mm to the domed area. I'm very curious to know what this measurement is in the 500. Every comparison picture I have seen showing the 450 and 500 piston show the 500 piston significantly shorter.

 

Interesting stuff - I am busy building and learning.

I am running 74mm pistons, having first pulled the stock sleeves out of the barrel, then had the barrel bored out, then had Wiseco big bore sleeves inserted, then had the Wiseco sleeves bored out to take the 74mm pistons - therefore giving me 2mm plus of sleeve wall. I preferred this to boring out the stock sleeves and running with 1.5mm or less of sleeve wall. I also had to bore out the upper crank case to take the ends of the Wiseco sleeves.

My head has been ported, polished and fitted with THR valves, and I am running Megacycle 'mild grind' cams so I can stick with torsion bars.

My cylinder has no base gasket (only threebond gasket cement) and I will be running a copper head gasket from THR (I think it is 1.5mm thick?).

The barrels are torqued down and the edge of each piston finishes dead flush with the top of the barrel on rotation of the crank.

After all of the calculating and allowing for .96mm stretch in the connecting rods at full heat - I have quite a close tolerance, so it will interesting to see what compression I get!

 

After acquiring a 1975 CB500T recently I found that my newly built workshop suddenly not is as big as it seamed so I decided to disassemble the 500T. Several parts will be used for the Bomber build but I have to get rid of a lot of parts too.

Before.

After.

Oh, since this Bomber frame has seen the hack saw can somebody please help me with measurements or a drawing of what the rear frame hoop is supposed to look like?
Is anything attached to the rear frame hoop on a Bomber?

 

Hi Ronny The hoop supports the seat there is nothing bolted to it. If you need precise measurements I will get these for you. I hope the pic helps

 

Pictures are a great help Nigel. I see it has to be high enough to give room for the rear fender and the wires.
Some measurements would be excellent.

 

I'm pretty sure the CB500T will go way bigger than 74mm.
I usually measure the narrowest diagonal between studs, 10mm smaller is max bore size (allows boring block and fitting new liners)
You can fit 74mm pistons into CB360, (2mm over is kinda a 'stock' fitting for extra 22cc, I've done 70mm, load more work)
I would think 500T will go to ~80+mm but it's a long time since I've had 450/500 in pieces Use Kawasaki KZ1000 drag race pistons (they go all the way to 82mm and have a high dome)

 

I also think it's possible to go much bigger than 74 mm with other sleeves as THR f.ex. sell 75.5 mm pistons. I'm determined though to bore out stock barrels.



Started work on the Bomber today by mounting a CB450 K5 centre stand and trying out Raask rearsets. As I've mentioned before I am missing many Bomber parts so I'm going to use what I have to get the bike rolling. It will in it's first version be a real bitsa but if I know myself correctly it will be a proper Bomber in a couple of years.

 

I have a bomber triple tree if you want to run stock front forks, otherwise if you use the 500T triple and forks you can swap and spin the forks and run the brake calliper at the rear of the disc on the right hand side.

 

I'm planning on using my CB450 K5 forks with a custom built 19" drum brake wheel. Perhaps silly by I can't get myself to mount a disc brake front wheel on a Bomber.