Topic: 73 500 Need explanation on over-boring

[calj737]

So dropped my jugs off. After rough bore and inspection, shop indicates I need a second over or 0.5 overbore. Does that indicate I need a kit for 572cc? A little explanation of displacement calculations would be most helpful.

Thanks!

[Powderman]

Is that mm or inches?

By my  calculations going with a .05mm over bore will take your motor from a 498cc to a 499cc. A big bore kit would not be necessary. In V8 engines typical over bore are either .010", .020", .030". A .05mm over bore is only .002"

I never realized how small a 500 motor is, 2.2" piston with a 2" stroke

[strynboen]

"think" first bore are 0,25 next are 0,50 next 0,75... last are 1,0 milimeter...but look piston seise first...

[calj737]

I didn't catch much explanation about the .5. He definitely said second over, indicating first over would not be sufficient to remove the damage in the cylinders from the corrosion.

My primary question is what size pistons do I order, 59's or 61s? And does that take the displacements two 572 as a result of second over bore?

[iron_worker]

Stock pistons are 59mm. 1st over woudl be 51.25mm. 2nd over would be 59.50mm, etc. You really should buy the pistons first so the machinist can measure them accurately and match the bores to them to give them correct piston to bore clearance for your application.

A first or second over bore wouldn't change the displacement much ... maybe a few CCs. If you go to 61mm pistons then the displacement will increase significantly (probably 572cc but I haven't verified that).

So basically, you need to decide at this point whether you want to go big bore at this point or not.

IW

[flatlander]

indeed. but are the 500's pistons not 56mm?
if you do an overbore in the regular steps as iron_worker describes you don't really need to get new pistons, just rings in the correct oversize. should only need new pistons if you go bigbore, i.e. more than the regular oversize rings which go up to 1mm, in 0.25mm intervals.

[Whaleman]

Flatlander, with all respect this advice is wrong. Dan

[IBleedHondaRed]

agreed^^^^

[alacrity]

Yes, I concur. Flatlander's advice is incorrect.  If you make the hole bigger, you need to make the piston bigger to match. There is a very specific and certain amount of space needed between piston skirt and cyl wall. Too tight or too loose - both NG.

I found a NOS "rocky" 1.0mm overbore kit with pistons, rings, pins, everything in miraculously PERFECT shape for $100 on ebay (from before it became Tucker-Rocky) .

The cyl boring at the machine shop, include decking the cylinder block (for perfect flatness) and honing was $200.

[flatlander]

Flatlander, with all respect this advice is wrong. Dan

no need for respect - i wrote crap and you guys spotted it, that's how it is!
edited it to strike-through so nobody's tempted to believe it.

[iron_worker]

You may be correct about the 56mm bit though. It may be that the 550 pistons are 59mm and the 500's are 56mm.

IW

[flatlander]

the 550 are 58.5mm. that i know coz that's what mine are now... and also need a rebore.

[dave500]

just buy 2nd oversize piston/ring set,unless you want to go big bore?once its big bored you cant bore it anymore.

[calj737]

Dave - Hoping you would show up... What are the stock MMs for 500s, and what is the displacement after "second overbore"? How big is "overbore" that the stock sleeves will tolerate? 536, 572?

[Trad]

a 60mm piston is a 572cc. I am running 60mm in my 550. The stock 550 sleeve can take up to a 61mm (592 CC) I'm not 100 percent sure if the 500 shares the same sleeve. Maybe someone can chime in on that.

[Powderman]

Bore and stroke of the CB500 is 56.0 x 50.6, the 550 is 58.8 x 50.6. An overbore of .5mm is only .019" and as I said before would yield less than 1 inch in increased displacement

[dave500]

PI r squared  x stroke x cylinders(4)

stock bore = 3.14 x 28 x 28 x 50.6 x 4 = 498

0.5 overbore = 3.14 x 28.25 x 28.25 x 50.6 x 4 = 507

the stock 550 bore is 58.5 = 544, mine has first over size = 548.5

you can use xl125 pistons in your 500,they have the same bore and wristpin height but a domed piston,i had a first oversize 500 using them,watch the compression ratio and piston clearance.


look what i found?.5 oversize xl125 piston sets.
http://www.ebay.com/itm/Piston-56-5mm-Rings-Kit-Honda-CG-125-XL125-CB125-JX125-/180655889213#ht_2484wt_878

[bryanj]

Just get a 500 2nd oversize (+0.5mm) piston/ring/pins/clips set.

If you can find a standard 550 piston kit set cheaper you can bore to those (esentialy a 12 oversize kit)

61 mm pistons(750 standard) can be used IF the machine shop is VERY good and carefull as teh liners get very thin.

550 liners are thicker than 500 liners and 550 cylinders will not fit (mostly) onto 500 cases.

You can get on ebay a 605 kit of liners, piston kits and gaskets whic costs more to do as you have to bore three times (block, inside liner and crankcase mouth) but it isn't relly 605 but a bout 599

Hope that helps

Bryan

[calj737]

Many thanks for all the examples and recommendations. Dave, I did know how to do the math, I was justin. The car traveling all day and couldn't get the time to search the stock bore and stroke for a 500. But am chuckling at myself as I guess I sounded rather stupid...

Haven't ever heard bores referred to as 1st, 2nd, overs etc. Very familiar with V8 engines and boring and stroking them.

I'm looking at a CycleX 59mm kit. MRieck recommended the kit as a good marriage for his Stage 3 heads (due to condition of the head, gonna need a lot of machining to set right). Any see a problem with these 59's in stock sleeves?

[dave500]

59mm = 550 2nd oversize pistons = 553,the sleeves will be thin around the spigot area where they slip into the upper case,you dont get much ramp lead in to feed the rings into the bore during installation,take care.

[cougar]

In reference to what was said by "iron-worker". Once you decide and buy what pistons you'll be running, then take them to whoever will be doing the boring. They should bore each cylinder to match a specific piston and then that piston should be kept with that cylinder. This is really the only "Correct" way to do it.    ...cougar...

[lucky]

In reference to what was said by "iron-worker". Once you decide and buy what pistons you'll be running, then take them to whoever will be doing the boring. They should bore each cylinder to match a specific piston and then that piston should be kept with that cylinder. This is really the only "Correct" way to do it.    ...cougar...

Cougar is right.

Right on with your bad self Cougar!!

[bryanj]

I have heard that a lot but in 30 years of using Honda Pistons i never yet found one that was measurably different from the stated size when new

[dave500]

my guy does a precision finish hone,hes fussy and takes time to make each bore correct for a piston no matter how slight the difference,its his pet thing,he races old six cylinder holden cars in a class where mininmal modifications are allowed to the engine,the better you can get the piston and ring to seal the slightest edge you have.

you need all the edge you can muster chasing v rods uphill!we didnt know this guy,he bull dozed through frostyboys cb750 ride we went on a little while ago,i have tim(kghost) on his kr250 right on my rear wheel all the way here and blocking his way,as barry sheene says an ounce of handling is worth a pound of horsepower,just go with the .5 rebore!excuse my missed shift at 2:44,look how much ground i lost!

v rod
as you have it all apart look in the intake runners/manifolds for this sort of production error and fix it,dont try and port larger just match up the connection and knock of any obvious lumps and casting flash flaws,if you run points dont pay too much attention to having both point gaps or dwell exactly the same,just be sure both pairs 1/4 and 2/3 end up firing exactly the same at full advance with a strobe(i use two stobes for this),forget about the "F"mark,where it idles so be it,just get them both firing the same at full advance,this is where these engines live anyway.

youll end up with an engine that runs a little sweeter than the others.

[calj737]

Dave - always enlightened by your contributions. Thinking I'll do the Wiseco 59s but for carbs, I'll be adding CR26 from Godferreys. I'll send the inn take spigots to Mike for port matching. Just gotta get on Mike's schedule now for the work.

Dropped the jugs to be final blasted and coated with Thermal Dispersion for improved cooling. Waiting on the head to be stripped of all the internals for powder costing, then being shipped to Mike with the valve cover. New cam and hard weld rockers on the docket too.

Problem is the engine was really neglected during storage for 27 years, so the valve train is really nasty. Better off just building it up from one time, properly with higher quality parts. The bike is. Going to my 19 year old, so it should have a very long life in our family. Amortized out over it's next life, and it's cost effective to do the build this way.

[jonda500]

Awesome handling vs's power vid dave! good to see I'm not alone in having occasional missed gears, and always pick up good tips in your posts (I will be putting new rings in my 500 soon!)