Topic: CB550 Top End Rebuild

[CJK]

After getting a new MotoGP Werks exhaust for Calj737, I went to install it and discovered the engine needs work (oil in exhaust port and corroded valves). Cal's response to the pic of the valves was something along the lines of "Holy @*%&@*%". I guess I like to impress

The Bike wasn't running great prior to this, as it was sitting for a couple years while I was away. I completed a 3K Service, but not much else since. I will be doing a cylinder leak down test to diagnose the full extent to the issues with the oil leaks, but I know for sure that the top end needs a rebuild.

I found a replacement head on eBay for $50, so I bought that. The new head came from a running bike (allegedly), and it looks significantly better than what's on my bike. There's slight surface rust on the valve stems and rocker arms, which looks like it will clean up easily.

Cal recommended that I have the mating surface milled flat, replace the top end gaskets, lap the valves, and bolt it back on. I have a CB650 Cam, which I planned to install so I'll do that upon re-assembly.

Once I do the leak down test (hopefully tomorrow), I'll know I can stop the rebuild at the top end. Otherwise, I'll set my sights on the cylinders, as well.

So far I need to buy:

• OEM Head gasket
• Engine oil seals

[bryanj]

If you are only going as far as base gasket you dont need engine seals but check that the rubber pucks are in the top SET that you buy. If you have to get a full set the only difference between a 500 and 550 one is the clutch cover gasket.

[CJK]

Thanks for the tip. I’ll make sure to get those rubber pucks (side note: what are they for?) I’ll look for a top end gasket set only as I’m not yet digging into the whole motor.

Is there much difference between Vesrah and NE sets?

I feel like I’ve heard both sides, but I’m curious which you’d buy.


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[bryanj]

I have used both with no problems, the "pucks" cover holes in the head where access is needed to nuts/bolts and are held in be the cam cover. I cant stress how important it is to read repeatedley and understand the manual on cam cover fitting or you will destroy the valves and guides

[Stev-o]

Be sure to look up the "rubber band trick" before installing your head. [or you'll risk bending a valve].  A good leak down test should give you info but a good valve job is usually key when rebuilding these old motors.  I've had good luck with Vesrah gaskets.

BTW - A rebuild of a "top end" usually includes rings and cylinder work [honing], however, you may not need that. Hopefully you'll only need a valve job.

[CJK]

Thanks Bryanj ad Stev-o for the advice. I performed the leak down test this evening, and my results indicate that only a valve job is needed, instead of a top-end rebuild as I was referring to earlier (thanks Stev-o for the info)

I used the harbor freight leak down tester but only used the PSI gauge and compared difference between air pressure in and air pressure once connected to cylinder. I did three tests each at various PSI (15, 25, and 40) and consistently saw about 5% drop across Cylinder 1,3,4 and about 10% drop at Cylinder 2. Most of the air leakage was heard through the crankcase via the oil dipstick hole.

I dropped the cylinder head off today at an automotive machine shop for resurfacing. Tomorrow AM, I'll be ordering the HG and seals.

I took some photos of the exhaust valves and port to show how ugly it looks. Photos will be uploaded is separate post as they are on my phone.

[CJK]

Cylinder 1

Cylinder 2


Cylinder 3


Cylinder 4



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[CJK]

Light rust on rockers of purchased head. Is that a concern?



I have not yet looked at the rockers currently on the bike.


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[dave500]

those rockers are fine,surface rust on non contact moving parts is not a worry,seeing you've got the head off buzz the floor out of those exhaust ports like this so you can see the entire valve seat,thatll make proper use of the exhaust pipe you plan to use,also look at the intakes runner to head mismatch,if it looks like this clean it up,theres no point in using a motor works gp pipe on a head like that except bragging rights.

[bryanj]

If you could hear air at the dipstick it is going past the rings

[CJK]

Dave - That's what I figured, but wanted to be sure. I planned to clean up the casting marks in the ports with a dremel while it's all apart similar to what Jonesy did (http://forums.sohc4.net/index.php?topic=17374.0), not taking significant material away as I don't have a flow bench and my name isn't MRieck.

Bryanj - I thought about 5% loss of PSI past the rings on a cold engine is not unusual. Would you recommend having the cylinders honed and replacing the piston rings while I'm at it?

[calj737]

If you could hear air at the dipstick it is going past the rings

+1
Time to have the piston-bore clearance checked, also the ring end gap. If within spec, a decent honing is all you’ll need. It’s very possible the rings are gummed up from sitting, and everything is useable. But a fresh hone will tighten up everything once it’s back together.

Dave500 gave great advice too. If the head is at the machinist’s, take the intakes too and have them Port matched, and the head ported intake and exhaust sides.

[BomberMann650]

Don't forget the carb jets!

[CJK]

If you could hear air at the dipstick it is going past the rings

+1
Time to have the piston-bore clearance checked, also the ring end gap. If within spec, a decent honing is all you’ll need. It’s very possible the rings are gummed up from sitting, and everything is useable. But a fresh hone will tighten up everything once it’s back together.

Dave500 gave great advice too. If the head is at the machinist’s, take the intakes too and have them Port matched, and the head ported intake and exhaust sides.

Thanks for the advice, Cal and Dave. I’ll call the machinist today and let them know I have more work for them.

Forgive my ignorance, but is there anything else I need to tell him besides that I want the intake port matched to the intakes and the head ported intake and exhaust sides? I.e. any specific characteristics of this cylinder head they should be aware of?

Depending on the cost, I’m also considering sending it to MRieck since he’s the SME.

Cal, regarding measuring the piston-bore clearance and ring-end gap...that tells me whether or not I can hone and use standard size rings or if I’ll need to have the cylinders bored out and use larger pistons and rings?


Bomberman650 - Can you elaborate on what you mean by “Don’t forget the carb jets”?

Clean them? Use correct jet size?



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[calj737]

If you’re considering MikeR, just skip your local guy and send the head and intakes to Mike. He will know what to do.

Yes, those measurements tell you about bore/ring size and whether yours are still good.

[BomberMann650]

When you port a head, it increases airflow potential measured in CFM.  That, plus a cam swap means you'll be pulling more atmosphere into the chamber. 
Without installing larger jets, the cylinders might not recieve enough fuel.  These little cb's do not like running lean A/F mixtures. 
MotoGP werks also advises increased jetting to compliment their pipe, in a stock head/carb setup.
You'll want to contact either jets r us or 6sigma racing to get some official carburetor jets delivered. 

There is a company that has shared the comparative results of different cnc porting jobs.  Their maximum gain (ports dimpled like golf balls) flows an additional 17% over original.

Cb500's came stock with 105 mains.  Those are what I put in my 550 with a 650 cam and smoothed intake tracts.  Would recommend starting there for jetting.

[bryanj]

Problem with carburation is that the rules do not always make sense,  i put a 750 kit on a 650 triumph and with no other mods it then ran rich

[calj737]

Cb500's came stock with 105 mains.

90s, 98s or 100s, not 105s are stock in the 500/550.

[BomberMann650]

Cb500's came stock with 105 mains.

90s, 98s or 100s, not 105s are stock in the 500/550.

I stand corrected.  Now I wonder how 105's ended up in the junkyard set of 627B's i purchased

[CJK]

Cb500's came stock with 105 mains.

90s, 98s or 100s, not 105s are stock in the 500/550.

I stand corrected.  Now I wonder how 105's ended up in the junkyard set of 627B's i purchased

Because Bigger jets always = more power!

The PO put 105’s on my 627B (that came on my 550 instead of the stock 022A)


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[dave500]

im running 100/40 with stock airbox and 4-1 pipe ports cleaned up.

[flatlander]

Because Bigger jets always = more power!

i can't tell if this is a joke? anyway, it's not true.

ask mike for his prices before you decide. if he's in a range  you can afford, let him do it. he knows these heads like no other, it will be a million times better than some random shop around the corner.
then order a range of keihin jets from jetsrus.com (no repros from keyster or such). probably you'll be ok with 90, 100, 105 to choose from but you could get one or two sizes larger as well, to be safe.
then i would recommend taking the bike to an experienced dyno operator to finalise the jetting. it saves a lot of time and hassle compared to plug chops.

[calj737]

ask mike for his prices before you decide. if he's in a range  you can afford, let him do it. he knows these heads like no other, it will be a million times better than some random shop around the corner.
then order a range of keihin jets from jetsrus.com (no repros from keyster or such). probably you'll be ok with 90, 100, 105 to choose from but you could get one or two sizes larger as well, to be safe.
then i would recommend taking the bike to an experienced dyno operator to finalise the jetting. it saves a lot of time and hassle compared to plug chops.

Mike’s prices are extremely reasonable, if not more affordable than most “shops” from my experience. I’ve had him do heads and a local shop, an Mike was less than my local shop for the same operations. Timing and shipping and other factors caused me to use the local guys. They did a nice job too, but Mike extracts every ounce of performance and perfection from these heads...

With a refreshed head, 650 cam, stock carbs and a MGP exhaust, 105s will probably be spot on. Don’t go lower than stock, that’s for sure. You’ll be breathing more air which will require more fuel. Induction (airbox or pods) will make more difference than the head work on jetting.

[bryanj]

I can personally recomend Mike, he did a 500 head for me and shipped it to the UK all for a very reasonable cost.

[CJK]

Because Bigger jets always = more power!

i can't tell if this is a joke? anyway, it's not true.

ask mike for his prices before you decide. if he's in a range  you can afford, let him do it. he knows these heads like no other, it will be a million times better than some random shop around the corner.
then order a range of keihin jets from jetsrus.com (no repros from keyster or such). probably you'll be ok with 90, 100, 105 to choose from but you could get one or two sizes larger as well, to be safe.
then i would recommend taking the bike to an experienced dyno operator to finalise the jetting. it saves a lot of time and hassle compared to plug chops.

I tried to make it clear I was joking by putting “always =“ but yes, just goofing since it seems like most people end up downsizing the jets the PO put in there.

Anyway, I reached out to Mike. I know he is probably the best in the world at what he does and charges a super reasonable price for the quality of work done (probably less than my local shop but with exponentially more experience.

I’m not opposed to it, just need to decide how much I’m willing to invest in the bike


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