Topic: Re: 650 overbore/550 engine hybrid underway...final stages

[paulages]

64mm pistons and rings arriving on tuesday. guess that makes this project a 718cc instead of a 740. damn, wanted to be just over a stock 750. 

[markymark]

Thanks guys,  from what I hear the valves intake on a cb650 are 4mm bigger and the exhaust valves are 3mm bigger.   That is a big difference considering you cant make them bigger in a 550,  NO ROOM. 

[markymark]

Here is another pic:)

[paulages]

there is another thread dedicated to the compatibility of the 550 and the 650. i was hoping to keep this one to the subject of this engine project...i'll need all the focus i can get without straying too much. 


and on that note, i'd like to take a poll:

what, besides obvious wear items (rod bolts, and other preciously torqued bolts, etc.) and parts measured to be out of spec. would you guys replace if you were me?

 i'll be adding the little oil squirter that lubricates the primary and cam chains on the 650 that wasn't on the 550, but i'm still nervous about keeping the old primary chain in there with all of the extra power it'll have. at $91 though, i'd like to feel like it's really necessary. the entire list of replacable bearings, etc. adds up quick though. never heard of trans. bearings failing on these bikes, but i'm wary of not just replacing everything i can while i'm in there.

[markymark]

Paulages, i read some time ago in another forum that you can put a 750 cam chain in there.  I have heard that you need too for the gain in power.  That being said, I don't see why you couldnt put a 650 chain in there.  I don't know if this helps, I am still a novice when it comes to the inards of an engine.  But, I did read a website from a guy in the 90's who did these overbore/conversions with much more power that said he put a 750 chain in to compensate.  Be terrible to brake a cam chain while riding hard.  I hear it can kill you. 

[paulages]

the entire top end is from a 650, including the cam chain. the primary chain is what i would think i need to worry about.

[markymark]

Ok this is the gem I found.  I couldnt do the search for this site with a regular search, I did it by a honda  picture search on yahoo.  Here is the link.  Should work. 

Hope you can gain something from this site. 

http://images.search.yahoo.com/search/images/view?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fp%3Dhonda%2Bcb550%26toggle%3D1%26cop%3Dmss%26ei%3DUTF-8%26fr%3Dyfp-t-501%26b%3D41&w=700&h=564&imgurl=www.langkilde.com%2F%7Eniels%2Fpix%2Fnl_honda_cb550.jpg&rurl=http%3A%2F%2Fwww.langkilde.com%2F%7Eniels%2Fhtml%2Fmc.html&size=95.2kB&name=nl_honda_cb550.jpg&p=honda+cb550&type=jpeg&no=56&tt=486&oid=9c9a07ff00858080&ei=UTF-8

[markymark]

Ok sorry, try this link it might take you right to it.

http://www.langkilde.com/~niels/html/mc/550Performance.html

[Ibsen]

Paulages, i read some time ago in another forum that you can put a 750 cam chain in there.  I have heard that you need too for the gain in power.  That being said, I don't see why you couldnt put a 650 chain in there.  I don't know if this helps, I am still a novice when it comes to the inards of an engine.  But, I did read a website from a guy in the 90's who did these overbore/conversions with much more power that said he put a 750 chain in to compensate.  Be terrible to brake a cam chain while riding hard.  I hear it can kill you. 

The 650 have got a HyVo cam chain. It won't fit the sprocket on the 550 crank.


And the 650 also have a tensioner for the primary chain, which I belive the 550 doesn't have.

[paulages]

i'm using the 650 crank and up, so accomodating the hyvo cam chain will not be a problem. both models use a hyvo primary chain. i mocked up the entire bottom end, and everything fit together fine.

i dropped a pile of parts off at my machine shop today. besides fitting 750 liners into the 650 cylinders, they are doing a few modifications to the 550 cases, including widening the openings for the sleeves in the top case, opening the slot for the cam chain and tensioner to match the 650 top end, and welding in the tower just off of the main oil gallery that feeds oil to the primary and cam chains in the 650. we took more measurements, and so far it appears that i will be able to keep the original oil passages to the top end, eliminating the external oil lines setup (i like the idea, but if it aint broke...). he seems to think that machining the crank end to accept the 550 stator will be hard, as the metal is heat treated, so we will be removing metal from the inside of the stator instead.

now...i'm keeping my fingers crossed to see if the pin height matches up on the new pistons.

oh yeah, i decided just to replace every bearing in the thing, no point going through all of this just to have some stupid ball bearing explode on me because i wanted to save a few bucks...

[cafe75-550]

Paul- got my pistons yesterday. center of pin to shoulder of piston is 24mm, or 1mm more than the 23mm center of pin to shoulder on the 550 pistons, and 1.5mm more than the 22.5mm (.885") pin to shoulder on the 650 pistons that Terry posted in my 650 pistons thread. Since you're using the 650 block, rods and crank that last one may be more important to you, based on what I've got off of my 550 I think I may be able swing it without the pistons hitting the head  , but its gonna be tight. Also, FYI, the pins on the pistons I got are seriously stuck in the pistons....

[paulages]

well aint that how d'ya do.

well...if the pin height is indeed that much higher, then i'll just have to work with taking material off the dome. my machinist seem to think that machining clearance in such a small amount wouldn't be a problem, but custom pistons may still be on the horizon...

by the way, i forget: are you using 750 sleeves in the 550 cylinders? or are you just boring the 550 cylinders to fit?

[cafe75-550]

Yeah, my thought as well, although I kind of expected a little of it. The 836 pistons I have are also a 24mm pin height, but I didn't know the pin height on the 650's was less than the 550's until I bought the pistons. I've measured my 550 engine when I only had the head off and came up with 1mm of clearance at TDC, so I may be in the same boat with the pistons (0 clearance not too good, only the head gasket for clearance). On an interesting note, I got a set of KZ650 pistons (62mm, with a 64mm overbore available), and they have a 4.5 mm pin height. Based on the fact that Dr. Tom is using Kawi pistons at 64mm and the KZ650's are the only ones I could come up with at that size (with the same pin diameter I might add) it would be interesting to know what he did with his....the dome height isn't the big problem either, the 650's have a 4mm dome from my calcs (dome to shoulder), the 811 pistons are at 3.5mm dome, with the slightly taller pin height. So total height is only .5mm off, but the shoulder height is going to be the possible contact point.

By the way, who and where is your machinist? I've figured out how to machine the sleeves on a friends lathe, but I still need someone to do the cylinder, sleeve and upper case bores (not to mention if I need to run a little off the piston shoulder....)

And I am running 750 sleeves, the 550 sleeves would go away with a 64mm bore...

Bryan

[paulages]

bryan-

i just measured my 550 and 650 pistons, and came up with a pin height of 23mm on both. i also get a 4mm dome height on the 650.

what is the dome height on the new pistons?

[cafe75-550]

3.5 mm for the dome, or 27.5mm from center of pin to the top of the dome. If my math is right, this is only .5mm taller overall than the 650 pistons, which would make sense for the increase in compression. The only issue then really is if the shoulder being 1mm higher will contact the head, I think we're in the clear on the valves and the combustion chamber. And, I don't think it would hurt the pistons any to take .5mm off of the shoulder, in fact, I think it wouldn't make a difference because the shoulder on these things is already machined...You can see in the picture the lip that comes up above the valve pocket, taking this down a touch would reduce the shoulder height, and since at least in my case, with ~1mm to play with plus the head gasket for the 550, I think .5mm would be sufficient, if neccessary at all....

[paulages]

well, i'm in a pickle now...just went to place my servicehonda order, and discovered that the "D" crankshaft bearings a re no longer available. better start a new thread about this one...

[cafe75-550]

Sorry to hear about the bearings, there has to be some way to figure that out...What are your thoughts on the pistons?

[paulages]

since all of my parts are at the machine shop, i can't really say for sure. but as you stated, we are dealiing with a pretty small amount of material here. if it's only necessary to machine 1mm off around the edge of the shoulder, it might be doable. not sure about the .5mm dome increase, as they have my head also. doesn't seem like much of an increase, but could affect valve clearance.

i lucked out, and have a machine shop almost within eyeshot of my house that does this stuff all day long. the place is called Dan Hall's (here in portland, or), and dan is taking this project on himself. he said he only does about 2 hours a day in the shop, so it'll take a couple of weeks at least. he's exactly who i was looking for though: someone familiar enough with what i'm trying to do and intersested enough in the oddness of it to help out in the brainstorming department. prices seem average. $200 to port and polish a head, $75 for an overbore and hone. he's $70/hr and very friendly and helpful.

[bryanj]

Dont care how much it costs, with all the mods you a doing a NEW primary chain is an absolut must!!! They go slack on a standard 500 and eat into the oil gallery from pump to filter and the one accross the engine feeding the mains. Either of these is an instant KA---BOOM

[paulages]

yeah, seems stupid not to replace everything in there. one of the old chains has less than 3000 miles on it, but it is still 30 years old after all. so far, my service honda order, not including head components, is over $400. ouch. this thing better work! in any case, the money's better spent giving me something to do through the rainy dismal portland winter than just making something that goes fast. besides, so far i'm only spending "bike money" (money generated by selling other bikes or parts). 

[pae]

On the large bore 550 I've seen, the oil line from the bottom was plugged and a SS line was ran from the galley to the ends of the head.

Cheers, Tom

I'd love to see/read more about the bike in the picture - links to more info?

Having just read through this thread over the weekend, I opened up Classic Motorcycle Mechanics and there's a report from a meet at mid-Ohio and the same bike. See ... http://www.classicmechanics.com/article3.htm. It's mentioned in the 4th paragraph. Hopefully someone will identify it from the picture that leads the story.

regards, Phil

[cafe75-550]

Phil-

The bike is actually a 550 with some 650 (and other) parts and belongs to Dr. Tom Marquardt. See the thread here http://www.sohc4.us/forums/index.php?topic=13820.0 for more info on this one....

[cafe75-550]

Paul-

I just measured the Henry Abe 605 pistons and came up with something you might want to know...They have a 23.5mm pin height, vs the 23mm for the stock 550/650 pistons....

[paulages]

makes sense, considering the 1mm difference from the piston to the top of the cylinder at TDC. easy way to increase compression. i don't know how much clearance the 650 had though, as it's already all apart. should have checked that. oh well...

[markymark]

Hope this isn't to far off the topic.

Will 750 header pipes work on a 650?  I want to put a 650 into my 550 but I can't finde rounded downpipes for a 650.  I don't like the sharp angles on the stock 650 exhaust.  I want the more classic rounded curve that I already have on my 550.  HELP.  Anyone know the diameter of a 650 pipe as aposed to the 750 at exhast out? Thanks for the input.