Topic: 605cc questions

[Scott S]

I've been on the look-out for a good 550 engine on which to base a big-bore rebuild for my '71 CB500. I think I've located a running '77 or '78 550K and now I have some questions about big bore 500/550's.

 I've done some searching and reading, but I still have a few unanswered questions:

 1) On the Henry Abe kits, it's reccomended to replace the oil ring. Just get the stock CB750 ring for this?

 2) I found a 605cc kit that is missing the head gasket. How big of a deal is it to find or make a proper head gasket for this? Is the missing gasket a deal killer for this particular kit?

 3) I already have a CB500 gasket kit. Can I use it on the 550 engine for all the other gaskets; the rubber head pucks, o-rings, misc. seals and stuff?

 4) If the 550 engine has a good transmission and bottom end, can I get away with doing all the work from the case up? I.E., bored out barrels, new pistons/rings, wrist pins, etc., and leave the rods and the rest of the bottom end alone?

 5) What about the cam chain and tensioner? Always replace or

 6) I've seen some posts about APE studs. Necessary on a mild 605cc engine?

 7) I have access to the 627B carbs on my CB500 (rebuilt and work great) as well as the stock carbs on the 550K. Which would be best for this build?

  Porting and polishing: worth it for a street bike? Which head would you use, the 500 or 550? I know the 500 would need bored, but other than that, any advantage to either one? Stock valve sizes?

 9) Camshaft: The 650 cam is popular, but by the time I piece together a cam, tach drive and replacement tach, why wouldn't I spend a few bucks more for a new cam and keep my stock gauges? If so, what are some good specs for a street cam?

 The purpose here is A) I like to fiddle. I enjoy the research, collecting parts and building something new, and B) a little more power in my CB500 with the better bottom end/transmission of the 550.
 Power focus will be on street riding and mid-range. I don't want or need a 12,000 rpm screamer.
 I know these are a lot of questions, but any help will be appreciated.

[bwaller]

1) Plan on using all standard CB750 rings. The two compression rings should direct swap. you'll need to widen the oil ring groove to use the 750 oil ring.

2) No. Cometic can supply either copper or CFM head gaskets for the 61mm bore.

3) Yes

4) I wouldn't, you don't know what shape the bottom end is in but theoretically yes.

5) Replace if hard or badly worn.

6) Not necessary in the case of the 500/550, but doesn't hurt either.

7) Either or. If the 627 are rebuilt use them, you will need to re-jet. If you use the 627B carbs use the matching manifolds. Replace the insulators if they're hard too.

What can you afford? Is it worth it...absolutely and doesn't need to be a full on race job either. At the very least match cleanly all the transitions and remove casting roughness. Money is always well spent on the head, it should be a focal point. For the street stock valves are fine.

9) I have a 592 with a Webcam 58a. Good power delivery for the street, as nice a power band as the stock engine, just more oomph everywhere. There are other good ones.

Good Luck.

10)

[Scott S]

 Thanks, Bwaller! This is all good information.
 Where did you get your cam? Directly from Web?

 I guess I need to find out how much the Cometic gasket will cost and maybe use that as a bargaining chip against the cost of the kit. Do you prefer copper or CFM? (And just what is CFM?)

[JBMorse]

I only have a couple of answers as I'm currently combining a 550 and 500. 
3. Yes, as answered above.  The heads are identical and the top end gaskets will all work.  The clutch cover gasket is different on the bottom end.
4. Probably, if it's from a good running bike.  Everybody kept telling me to check the primary chain on my 550 bottom.  There does seem to be some difference between my new replacement and the old one in terms of wear, but I don't know of any spec on this so I don't know just how long it would have gone on the old one.  I sort of wish I'd left it alone because I am still without a bike to ride! That said, a case split is not difficult.  I can't yet speak to the difficulty of a case assembly 
5. There are a couple of good BryanJ posts on the condition of cam chain tensioner blades.  Grooves are normal, but you don't want them too deep. Do some searching for advice on what they should look like.
8. I had this exact same question.  I wrote to Mike Reick and he told me that for street application, he would recommend cleaning up around the valve guide bosses.  Not a real expensive job but it apparently makes a big difference.  Try emailing him for more info.  Again, I think the 550 and 500 heads are identical (except perhaps the 550f)

I went back and forth on this question of how much I should do on the head.  I haven't got it apart to see how things look but if the valves and guides are good I'm just going to relap and reassemble.  If they're worn I'll start saving up for valves and guides and get a good valve job done.  Kibblewhite now makes stock and oversize valves for these bikes.  I wish they were cheaper but at least they're available.

[Scott S]

 If I have to use Cometic for the head gasket, I'm sure they could make me a base gasket. At that point, why couldn't I find a set of good, used CB750 pistons and forgoe the cost of the aftermarket 605 kit? Are the wrist pins different? I mean, if I need to source gaskets and rings, I'm sure I can find pistons cheap. The machine work would still be the same. (BTW, I'm assuming the 61mm bore is stock CB750 since I'm being told to use those rings....).

[bwaller]

For the street I'd recommend a CFM (fibre) because although copper is good for high compression they will always show some oil weeping. Standard CB750 bore is 61mm. Do a search for the Gentleman's Express article on here and it gives exactly what needs to be done to re-work a 750 piston for the 500/550's. It'll take a machine shop more time to do than just widen the oil ring groove on the H-Abe pistons, BUT you'll have Honda quality pistons. The wristpin diameter is the same. Some guys here have doe it and may speak up.

Be careful with old used pistons, sometimes you can find a hot deal on new ones.

[crazypj]

The '605' kit using 61mm pistons is really 591cc
 I have a set of 0.75mm over CB750 pistons if anyone want's them for a 605?
 You'll have to find rings and pins though as I only have the pistons. I'm not sure if they fit in stock 550 liners? (61.75mm bore)
 My 550 is pretty tired (106,000miles)
 It's also 4,500 miles away so not sure if or when I'll ever get to it
I use copper gaskets (Lani, Copper Gaskets Unlimited) He can make  head and/or base gasket with any size holes you want plus has a selection of copper thicknesses (I think from 0.016"to 0.080")
 If you use copper(even if you don't) I find its a really good idea to counter bore the oil feed holes in block and fit dowels to support 'O' rings.
 Pretty much totally cures the 5,000 mile leak 500/550 is well known for. (works until the o-rings brak, around 25~30,000 miles)

[Scott S]

 PJ, can you elaborate or point me to a thread about the oil feed holes?

[crazypj]

The head gasket oil leak is well known 'feature' on 550's but as far as I know I'm the only one who ever bothered to 'fix' the problem.
 I counter bore oil feed hole for dowel and slightly enlarge diameter where 'O' ring fits
 Usual answer is to fit new head gasket and 'o' rings on outside of block when the oil reaches 3rd fin down or gets too irritating seeing the leak

[Scott S]

 So, I'm browsing ebay and looking at CB750 pistons....
 If I need to buy rings anyway, and the only 605cc kit I can find right now is missing a gasket, which means a call to Cometic....why not just buy some NOS CB750 pistons and rings?

 I think if I shop carefully, I can put together a set of pistons and rings, genuine Honda, for less than the 605 kit. But what years would work? I see them listed as '69-72, some for the later K models, some for the F models. Obviously, I can't use anything over a standard size or for the DOHC, but is there a difference in the SOHC CB750 pistons?

 I "think" I need part #13101-300-20. Is that the 61mm std. piston that can be used on a 550 engine to achieve 605cc?

[Scott S]

 And while we're at it...CycleX has some very reasonably priced "1st over", 61.25mm kits. Is 61mm the max bore for the 550 big bore?

[crazypj]

I'm not sure as I haven't tried it but I think the 61.25 would work.
 I would use copper gaskets (head and base) as they provide better heat transfer
 I get them from Lani at Copper Gaskets Unlimited.
 He also does different thicknesses so you can get close to 'correct'  squish (about 0.038"~0.040")

[TwoTired]

I'm not sure as I haven't tried it but I think the 61.25 would work.
 I would use copper gaskets (head and base) as they provide better heat transfer
 I get them from Lani at Copper Gaskets Unlimited.
 He also does different thicknesses so you can get close to 'correct'  squish (about 0.038"~0.040")

That's good info.

Do you happen to recall how thin the sleeves can get before problems arise?

Cheers,

[Scott S]

 And when you say "close to correct squish", is that deck height? Will I need to re-measure and re-calculate deck height if the pistons have the same wrist pin height?
 Give me a quick primer on what you do/measure to figure out the thickness of the gaskets needed.
 
  This all sounds really familiar to some of the hi-po VW stuff I've done, but that's always been with a complete rebuild, stroker cranks, new heads, etc. I never even thought about having to recalculate deck height, compression ratio, etc. if I used one of the 605 kits.

[Pain]

have you checked out dynoman.net? they have some kind of coupon deal going on right now that i'm gonna take advantage of. i had the same piston kit and was worried about everything you are right now... i sold it. i'm getting the race pistons off dynoman when my pay check drops thursday. if u buy those pistons now u get $100 off a future purchase - which will be a race clutch - which will give me $50 off another future purchase - which will get me intake manifolds.

[crazypj]

And when you say "close to correct squish", is that deck height? Will I need to re-measure and re-calculate deck height if the pistons have the same wrist pin height?
 Give me a quick primer on what you do/measure to figure out the thickness of the gaskets needed.
 
  This all sounds really familiar to some of the hi-po VW stuff I've done, but that's always been with a complete rebuild, stroker cranks, new heads, etc. I never even thought about having to recalculate deck height, compression ratio, etc. if I used one of the 605 kits.

 You have to do some minor machining on piston crowns, there is a picture with measurements in here somewhere (I think it's in 'Gentleman's Express'?)
 Deck height is what it's called in automotive, I guess you use same measurements for bikes.
 You can only thin the top so much so piston will probably be sticking out of cylinder slightly.
 Personally, I don't worry about calculated compression, dynamic compression is really what matters and hats dependent on cam - lift, duration, lobe separation, etc. I always run motor then do a compression check, rarely have to do any mods (probably because I'm lucky  )

[Scott S]

 Hmmm, this is sounding more and more complicated....
 Machine the piston tops....that's for the CB750 pistons? Do the 591/605cc kits need machining? I would hope not.

 What about the 61.25mm bore?  Like Two Tired asked, how thin are the sleeves at that point?

[Scott S]

 The guy on ebay with the 605 kit turned down my offer. I would need a $50-60 gasket, plus new 750 rings. That would put me at approx. $475 to use that kit.
 I'd love to hear from anyone that's done the CB750 piston version. Does it makes sense, dollarwise, to machine those pistons, etc.?

[RAFster122s]

Scott, You'll never get out of the bike the money you put into it unless it is stock or cosmetically the hot thing someone wants.  Only you can determine if your investment in the bike's performance will make you happy.

The Henry Abe kit is known to have ring issues and there have been a few cases where the liners dropped after the initial install causing the motor to have problems requiring more work and the like. 

Start pricing the machine work as overboring gets pricey. If you can safely bore it to fit the 750 pistons for the gentleman's express version it is a good upgrade with lots of torque and hp potential. But you'll need head work to take advantage of that additional displacement and if I recall correctly the Gentleman's Express design is a low to moderate compression design, so it won't be a high rpm screamer.
The pistons will need the crown relief and deck height carefully measured and valve recesses cut into the piston tops so it will work. Not difficult work for a machine shop but it isn't cheap work since they are doing 4 pistons.

Read the articles on the gentleman's express build and start calling around to find machine shops that do motorcycle work and tell them what you are wanting and get quotes to start pricing you project.
Then save your pennies and do the project.

Read the hybrid 650/550 motor threads and the Gentleman's Express build threads, there are several. Then cast your lot in one direction and see it through.

David
 

[Scott S]

 Hey David,
  I'm looking to build something along the lines of the Gentleman's Express. That's my goal. I'm not looking for a high RPM screamer, just good low and mid range performance.  Mildly warmed up.

 I'm not worried about getting the money back out of it (although I haven't lost money on a bike or VW I built yet), I just don't want to waste my money if it could have been better spent elsewhere.

 I won't be using the liners since it'll be based on a 550, not a 500.

 I sent a PM to a forum member here who does the piston mods, but he hasn't been active on the forums since December. Can anyone else recommend a shop that has done this mod before and is familiar with it?

 Not sure what you mean about the hybrid 650/550 threads, unless you're referring to the 650 cam swap?
 

[RAFster122s]

The 650/550 hybrid is a motor combination that paulages documented.  It is a lot more than just the cam. 

The. Gentleman's Express gives you a lot more torque in low & mid range and paired w head work & 650 or webcams 58a cam will give you more rwhp and a more enjoyable ride.
 I'll add a link or two when I'm not replying w my phone...

David

[RAFster122s]

Paulages' How To on the 550/650 hybrid motor
http://forums.sohc4.net/index.php?topic=40414.0

Another thread you might want to read:
http://forums.sohc4.net/index.php?topic=27827.0

[crazypj]

I've done the CB750 piston mods as kits were not available in Britain when I did mine (1978)
I would probably do things different today, swap liners and modify lightweight 350 'race' pistons (65mm)
My 550 was the first inline four I modified, now I've done hundreds of modded motors
 Main thing is, I can do all my own machining so I don't have to factor that into the initial outlay (I usually keep bikes until they wear out anyway  )

[Scott S]

 Did you swap liners in order to fit the 65mm bore? Was this on a 500or 550? Would the 550 liners have enough meat for the 65mm bore?
 reason I ask: I can find a 61.25mm 750 kit. I'd still have to have the piston tops and skirts machined, though.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200404490704&ssPageName=STRK:MEWAX:IT#ht_1940wt_982

PJ, are you set up to do the 750/550 mods now? Or, do you know anyone that can?

[bwaller]

I have both stock and bored sleeves so here's the news. Stock CB550 liners, measured at the bottom tapered part of the sleeve =3mm thick. After boring for 61mm pistons that section is 1.62mm (0.064") Boring further for 61.25 pistons leaves them very thin.

My 0.02, change sleeves if going bigger than 61mm. BUT you never know until you try so be my guest.