cylinder condition opinion (Picture included)

[Racincc85]

Hey guys - I pulled the head today on my 1984 honda CB700sc (700cc air cooled inline 4) motorcycle to replace the valve stem seals due to excessive oil burning on deceleration. I've never pulled a head before and don't know what to make of the condition of the cylinders so I thought I'd post a pic and see what you guys thought.



There are no deep gashes or cuts in the walls but there is plenty of carbon on the piston tops. What would be the best way to clean all of that crap off? Thanks!

[UncleBob]

can't see much in that pic. but I don't see anything scary

if you want to really check things out, pull the cylinders off.

IMO, I'd at least ball hone the cylinders and re-ring the pistons while you're there.

[Racincc85]

Sorry for the bad picture. Thanks for the opinion though! I did think about re-ringing the pistons but the bike only has 33k on it so is it really necessary? I'm tight on cash and it'll cost another $100 for a complete ring kit. It ran well before disassembly other than the fact that it burned oil awfully due to the bad valve stem seals. Also, whats the best way to remove all the carbon and crap? Soak it will carb cleaner?

[UncleBob]

Originally Posted by Racincc85

Sorry for the bad picture. Thanks for the opinion though! I did think about re-ringing the pistons but the bike only has 33k on it so is it really necessary? I'm tight on cash and it'll cost another $100 for a complete ring kit. It ran well before disassembly other than the fact that it burned oil awfully due to the bad valve stem seals. Also, whats the best way to remove all the carbon and crap? Soak it will carb cleaner?

depends who you ask. Many would tell you 33K miles is rebuild time for a bike.

IMO, if you were burning oil, thats enough reason. Nothing worse than putting it all back together and finding it still burns oil

until you inspect the piston rings, I definitely wouldn't make any assumptions

[Racincc85]

Good point. I've put so much time into this thing so far I might as well do it right so I only have to do it once. I'll have to sell some of my air tools to pay for it but fun does come at a price unfortunately. I took a closer look at the cylinders and all of the crosshatching is gone. I'll get a micrometer and measure the diameter of the cylinders to see if they are still in spec. If they are and I just go with the ball hone would I use standard size rings instead of oversize? On the bright side all the bearings are in good shape. I had the bottom end apart in the summer to replace the alternator chain and everything looked good.

One more thing - can I use a regular piston ring compressor to reinstall the pistons or do I have to use a special one since the pistons are installed to the bottom of the cylinders instead of the top?

[UncleBob]

I can't speak for the CB700 specifically, but most bikes have a too short of a stroke to use normal ring compressors. Not enough room for the tool

I use a small pick or screw driver and *carefully* work the rings in. Its not very hard but it takes patience

Its not uncommon for the cross hatch to be worn away. I wouldn't stress about that. But you do want to look for excessive blowby under the rings, and carbon build up in the ring lands. Get a bore gauge, and check for taper or egging

Honda would have offered oversized pistons, but with the age of the bike you may not be able to get them anymore. You could get aftermarket pistons, but your eally don't want to know how much that would cost....usually around $700

Most likely your cylinders are fine. All you will need is rings and a quick hone

[curtis73]

UncleBob is wise. He kicks enough a$$ that I would listen to him

I'll just add my opinion. I've done a few CBs and found that most of the oil burning usually happens in the head. I did have one that I rebuilt the head and found that it was actually the rings leaking oil and I continued to run it for three years. I just changed the plugs more frequently.

CBs are pretty reliable. The early single cam CBs are a little more bulletproof, but the later ones are perfectly viable. I just sold an 84 SS that had 87,000 on the original assembly... which is a lot in reference to older bikes.

As far as getting the rings in: I used a set of channel locks to lightly compress the sides of the rings, then I used a pair of needle-nose pliers wrapped with electrical tape to push in on the gap without galling the rings. It took a bit of finesse but it worked.

[Racincc85]

thanks for the advice guys. A buddy of mine is buying my air tools that I don't absolutely need so I've got the cash to do this how. One set of rings and a hone coming up!

[Racincc85]

Update - I just got the cylinder block off and all looks good. There was no evidence of blowby (which I'm guessing would be carbon deposits under the compression rings) and the cylinders looked good. This is actually turning out to be a fun project. I've never re-rung a motor before so it's one more thing I can check off the list!

[UncleBob]

take some pics of a piston

[Moppie]

Go on Bob, you know you want to recommend a turbo....

[Racincc85]

^ with the way the carbs are set up on this bike that would be one hell of an interesting pressure box to build!

Anyways, I had a picture of a piston but my friend deleted everything off of my camera and I've already got the pistons cleaned up so I can't take another. I found some pictures on another website of pistons from engines with blowby and mine didn't show any of the signs.

The flex hone I ordered should be here tomorrow so hopefully I can get this thing back together this week and see how it runs. Spring break is over so I've got limited time to work on it now. I'm also going to try installing the pistons without the ring compressors. Should be an interesting excercise for my patience

[UncleBob]

Originally Posted by Racincc85

^ with the way the carbs are set up on this bike that would be one hell of an interesting pressure box to build!

nah, its real easy. Don't need to build a box covering the whole carb, just the inlets

[Racincc85]

this turbo idea is intriguing now... I think you just spent my next few paychecks!

I had another idea for compressing the rings - would a solid stainless steel hose clamp work?

[UncleBob]

Originally Posted by Racincc85

this turbo idea is intriguing now... I think you just spent my next few paychecks!

I had another idea for compressing the rings - would a solid stainless steel hose clamp work?

hehe, its dangerous to talk to me, if you like doubling the power of bikes.....I've been known to make a lot of people broke with my encouragement

The top two rings are the difficult ones. The oil rings usually go right in without trouble. You could definitely give it a wirl with the hose clamps. I've gotten good with the pick-method, and it only takes me 5 minutes to get the cylinders on, so I've never tried that method