Topic: 550/650 hybrid or 650 big bore HOW TO

[paulages]

First off, GREAT THREAD!!!!!!
So much good info here!
Too much to digest in one sitting.
Forgive me if I'm being redundant here, but if you have a relatively quick answer, I would greatly appreciate it.
Taking the CB550 (or 500 motor) AS IT IS...i.e. NOT replacing the cylinders or head, what would you recommend as the best route to gain reliable, quick HP improvement?
The 650 cam is a bolt-in, if I read correctly. Does this require advancing stock cam timing?
What are the largest liners and pistons that will work with the stock 500/550 head without reducing or raising the CR beyond acceptable levels?
Is there a better carb setup (that won't cost a fortune) or a reliable carb mod that provide the right fuel/air mixture for the modded engine?
Which is the best reasonably priced exhaust/what style (4-into-one, I assume?)
Thanks in advance for your help!

i think most of your questions are best suited for another thread, or the search function, but the short answer to your first question is head work and a good cam. next, dislacement/CR. look around on the forum... lots of good info on here.

[Captainkirk]

i think most of your questions are best suited for another thread, or the search function, but the short answer to your first question is head work and a good cam. next, dislacement/CR. look around on the forum... lots of good info on here.

Thanks, Paul. I will be starting another thread, probably in the Projects forum.
Just curious.....if you had to build another 718 today, at *average* costs, what would you expect it to run, including gaskets, bearings, rings, new pistons/liners and machining? (a ballpark estimate would be fine)
I'm seriously thinking of doing this, but I'm afraid the costs might be outside my budget for the project, which is why I asked my original questions about using the stock head and cylinder casting.

[paulages]

I'm not sure I can estimate that, but I'm starting a new project for someone else... RC166 replica with a 762cc cb550/650 engine. I'll be starting in the engine soon, so stay tuned.

[pdxPope]

You are such a masochist. 




-JP

[scunny]

subscribed. thanks for putting yourself thru this Paul. 

[Captainkirk]

I'm not sure I can estimate that, but I'm starting a new project for someone else... RC166 replica with a 762cc cb550/650 engine. I'll be starting in the engine soon, so stay tuned.

Waiting, with bated breath......

[KeithTurk]

We're contemplating this exact project.... should be fun....

Thanks for being so detailed oriented Paul

[Sam Green Racing]

We're contemplating this exact project.... should be fun....

Thanks for being so detailed oriented Paul

a much nicer crowd in HERE Keith.

Sam.

[paulages]

We're contemplating this exact project.... should be fun....

Thanks for being so detailed oriented Paul

Funny you say that, because I feel like I left out a lot of details. This next project I plan to document fully, and post the entire engine build step by step in one post, so that it won't get too cluttered with responses at first. Kind of a "rebuild for dummies" on a 500/550/650, but with the fun stuff thrown in.

[FrankenFrankenstuff]

a fine recipe....now I just need a 650

[sinister902]

Funny you say that, because I feel like I left out a lot of details. This next project I plan to document fully, and post the entire engine build step by step in one post, so that it won't get too cluttered with responses at first. Kind of a "rebuild for dummies" on a 500/550/650, but with the fun stuff thrown in.

This is something I EAGERLY await....I've been trying to source a 650 lump for some time now...

[Ricky_Racer]

Me, too!  I've got the 550 roller, and the '79 650 lump sittin' on the floor! Can't wait to start laying out this combo!      RR

[mcarboni]

Yes 61mm pistons WILL work in a stock liner for a cb650.
I got a set of '77 high domed cb750 61mm pistons in my '79 cb650 now.
God I love 'em!

Actually 62mm is the limit.
But I have been stumped as to where to get 62mm pistons....
Hey.. 1mm over cb650 pistons... Duh.(brain fart)
I wonder if DSS has any left.......
I have thought of the KZ650 pistons(62mm), but have not bought a set due to lack of availability of rings.
No point in trying them if I can't seal the cylinder properly in the end!


But anyways... on those '77 cb750 pistons I used....
I guess I bumped the CR mabey .25 to .5 higher with them.
not sure offhand.
I know the cylinder pressure has leveled off at around 180-190 psi with the pressure tester I have been using.


The '69-'76 pistons would actually DROP the CR quite a bit I would think.
Mabey good for a turbo application? Dunno... got a set of (?'72, '73?) pistons I am thinking of checking clearances for and doing that in the future though.....
Gotta find a good turbo first though.. and finish my 66mm cb650 first as well....
(My "wish list" for my cb650 motors is quite long.)


The cb750 pistons I used needed a bit of modding though.
I had to re-position and deepen the valve pockets, and cut a bit off the outter edge to re-establish the deck height to what the stock cb650 pistons were.
Beyond that, not a lot.
I think I re-contoured the dome (without removing any height) to look blend into the land I had cut for the deck height.


Sorry, no measurements offhand.
Still can't find those sketches.


However I recently got a job again, WHOHOO!!!@!
(after nearly 4 months off work!!)
I will be  modding a few sets of cb750 pistons in the near future.(for me and others)
Sooooo....the "print" (poorly done sketch with measurements) will be scanned so I can post it on here for all to see of the mods I make.
Might not give everything, but I will add notes that SHOULD give enough info to a competent machinist to copy the work I have done.


I might even make the measurements readable to other humans!
hahaha....
You would have to see my box of "prints" for all my custom doo-hickeys I have made over the past 10 years to really understand.....
I have to decipher them at times.


Head up, rubber down, balls out!


l8r

I've been looking around for some 77-78 high dome cb750 pistons but haven't come across any. I do see a lot of the early DOHC CB750 pistons on ebay that have the high tops on them. They are not exactly "domed" but have like a rectangular raised area running down the center of the top. Would these work? Obviously they would need some machine work but would the shape of the top raise any problems?

*edit*
I'm looking at these in particular because I'd like to stick to using the cb650 sleeves.

[paulages]

Soos has been MIA for a bit, so you may be on your own figuring this one out. As long as the pin diameter is 15mm and the pin to shoulder height is relatively close, it should be doable. The issue with the dome is making sure enough crown is in the combustion chamber that the compression ratio stays high enough. If you look at the 64mm pistons I used first, they're flat topped, which should be better for gas flow. These had enough meat in the crowns that the shoulder could be machined to a suitable squish and enough of the crown was left to fill the chamber at TDC to make a decent CR.

[Pinhead]

IIRC, Soos once said that DOHC750 pistons are impossible to use...

[paulages]

IIRC, Soos once said that DOHC750 pistons are impossible to use...

Yeah, I think the wrist pin diameter is wrong.

[mcarboni]

This might be a pretty dumb question but is there somewhere I can find an abundance of dimensions and specs for various pistons? That would just be too good to be true wouldn't it.

How about something like cb175 pistons? I think they're somewhere around 62mm. According to Soos, one could get away with still keeping cb650 sleeves. Looks like they have plenty of material to work with on the dome, but again I don't know what the wrist pin diameter is on them. Any other suggestions?

Paul you got pistons lying around at the shop that you think might work with some machining? I might be dropping by this Sat.

[paulages]

This might be a pretty dumb question but is there somewhere I can find an abundance of dimensions and specs for various pistons? That would just be too good to be true wouldn't it.

How about something like cb175 pistons? I think they're somewhere around 62mm. According to Soos, one could get away with still keeping cb650 sleeves. Looks like they have plenty of material to work with on the dome, but again I don't know what the wrist pin diameter is on them. Any other suggestions?

Paul you got pistons lying around at the shop that you think might work with some machining? I might be dropping by this Sat.

I don't have anything sitting around that would be helpful.. we already know CB350T pistons are what became the 811 and 836 kits, and I believe the dead cl175 engine I had went out the door. Ask around in the hi-perf section.. lots of those euro guys know what pistons work for the 500cc classes.

[mlinder]

This might be a pretty dumb question but is there somewhere I can find an abundance of dimensions and specs for various pistons? That would just be too good to be true wouldn't it.

How about something like cb175 pistons? I think they're somewhere around 62mm. According to Soos, one could get away with still keeping cb650 sleeves. Looks like they have plenty of material to work with on the dome, but again I don't know what the wrist pin diameter is on them. Any other suggestions?

Paul you got pistons lying around at the shop that you think might work with some machining? I might be dropping by this Sat.

Mike, CB175 pistons are 52mm.

I think Paul and I looked at the wiseco xr200 pistons I was using for a cb350 build in relation to his other pistons, but those may be a little bigger than you can go witht he 650 sleeves. They start at about 64 or 65mm, can't remember. They's also absolutely need work to get squishband correct.

[mcarboni]

Mike, CB175 pistons are 52mm.

I think Paul and I looked at the wiseco xr200 pistons I was using for a cb350 build in relation to his other pistons, but those may be a little bigger than you can go witht he 650 sleeves. They start at about 64 or 65mm, can't remember. They's also absolutely need work to get squishband correct.

Hey mark, I think I might have found my pistons. I started another thread in regards to piston options. ffjmoore has some 77 cb750f pistons that will work well (with some machine work done on the dome) that we've been messaging about. I'm just having a hard time now finding rings for these pistons. I called Total Seal and they told me they just made a batch for someone and that contacting that person might be the easiest way to get a hold of some of those rings. Turns out that someone is a member on this forum as well. I've sent a pm but haven't heard back yet. I might have to contact Total Seal again and get a quote or possibly have the pistons machined to take the 750k rings.

[bwaller]

The thread is just down a ways on the SOHCbikes section, maybe post there?

[thrutheframe]

+1 for how the heck is a guy supposed to finish anything when all this killer info is available to make him/me wanna go further with a project bike??

[turboguzzi]

just to remind you guys that KZ 650 and kz/gpz750 pistons have 15mm pins..... 

have a used but good set of GPZ 66mm high dome set sitting on my table if any of you wants...

TG

[paulages]

just to remind you guys that KZ 650 and kz/gpz750 pistons have 15mm pins..... 

have a used but good set of GPZ 66mm high dome set sitting on my table if any of you wants...

TG

I'll take them with some measurements, please... Shoulder height? Soos was hooking me up with some for the RC181 replica, but he went MIA a while back.

[benjy]

turbo guzzi is correct.when the 1st 720 big bore kit came out for the kz650 kawa,a friend of mine used it in his kawa,+ I nstalled his fairly new standard pistons in my K1 750.the increase in CR gave me a very real improvement in torque.the dome shape,as I recall,is rounder than the steeper step,of some aftermarket kits