Topic: 1974 CB550 Ticking After Top End Rebuild + Cam Swap

[Mkubs]

Howdy folks - it's been a while, but I've tried a few different things that I thought I'd list out here...

• Re-installed the exhaust/headers to ensure there is no exhaust leak
• Re-lapped the valve and valve seats
• Swapped cylinder heads with different valves because I thought it may have been my valves and valve guides

None of these got rid of the tapping sound. However, I did the classic screwdriver to the ear trick and pinpointed that a fair amount of the tapping was concentrated at the cylinders. Which made me think there may be something wrong with my pistons.
I looked into piston slapping, and now I think that's exactly what's happening. I checked my pistons a while back and noticed that they can pivot quite substantially about the wrist pin, but I didn't think anything of it because it seemed like the rings were still making solid contact. I attached pictures for feedback. I plan on taking the top end apart again (for the 4th time!!) to measure the bore, the pistons, and the rings.
Maybe I completely missed that my cylinders have been bored out? I don't know, but I'll definitely  be checking this weekend.
Let me know what you guys think!

Thanks!

[Mkubs]

Just measured the diameter of the old pistons....they are 58.95-59mm in diameter.
I'm going to swap the old pistons back in and put new, oversized rings in them.

[RAFster122s]

Your old pistons were larger than stock if they measure at 59mm...if you are measuring with calipers then how much measurement error do you have?  Stock is 58.5mm diameter...

What type of hone did you use and what did the cylinders measure after honing?
It is not uncommon for cylinders to have eccentric wear, honing alone cannot correct this issue.

Align boring the cylinders to reestablish the cylinder alignment can restore some lost power from the cylinders drifting during initial break in when the material around the liners allowed the cylinders not to remain in alignment with the crankshaft. The metal for the cylinder surround was not ideal. Align boring restores that lost power, it is a one time issue as after break-in the material surrounding the cylinder liners stabilizes.

[calj737]

The picture of those 3 bores does not show much in the way of honing marks. Remind us, what compression values did you get for each cylinder? Are you detecting any blow-by last the rings?

[Mkubs]

Your old pistons were larger than stock if they measure at 59mm...if you are measuring with calipers then how much measurement error do you have?  Stock is 58.5mm diameter...

What type of hone did you use and what did the cylinders measure after honing?
It is not uncommon for cylinders to have eccentric wear, honing alone cannot correct this issue.

Align boring the cylinders to reestablish the cylinder alignment can restore some lost power from the cylinders drifting during initial break in when the material around the liners allowed the cylinders not to remain in alignment with the crankshaft. The metal for the cylinder surround was not ideal. Align boring restores that lost power, it is a one time issue as after break-in the material surrounding the cylinder liners stabilizes.

I need to get back into the cylinder to measure the diameter after honing.
I used the typical stone hone - https://www.common-motor.com/honda-motorcycle-cylinder-hone?srsltid=AfmBOopSlxKWhOVODCYMjrmYyyAUAF3GWs1BIFPhTn_cLwrNVXwY8FnI

From what I've read though, the piston to bore clearance for these is supposed to be no more than 0.026mm. My naive self didn't measure the current clearance, but it certainly looks to be more than 0.026mm. Hence why I think there might be piston slapping.

The picture of those 3 bores does not show much in the way of honing marks. Remind us, what compression values did you get for each cylinder? Are you detecting any blow-by last the rings?

Apologies, I should've clarified - the pictures are of the same cylinder. I was attempting to display the front to back play of the piston to the bore. I could be wrong, but is that not way too much space? Hence my thought that there is piston slapping.

Before the rebuild, the compression was measured at the following:

• C1: 63psi
• C2 and C3: 60psi
• C4: 68psi

I still have to measure the compression after the piston and ring replacement, but each time I went into the engine, there was some sort of oil (and possibly water?) mixture. From what I've read, this could be due to the rings settling in and the engine needing to burn off the oil. I did go back in to re-align the rings to be oriented per the manuals instructions.

[bryanj]

That looks too big to me

[Mkubs]

That looks too big to me

I assume you're referring to the gap, correct?

[bryanj]

Correct, but the only way to be certain is remove the cylinders plus one piston then check ring gaps and piston skirt clearance

[calj737]

Correct, but the only way to be certain is remove the cylinders plus one piston then check ring gaps and piston skirt clearance

+1

[Mkubs]

Got back into the engine today. Here are the following measurement...

• Bore diameter of all 4 cylinders: 59.00mm (+/-0.02mm)
• Diameter of piston skirt: 58.5mm

The new pistons that I put in here were part of a kit. Therefore, if the pistons are undersized, the rings will be as well. Now that that's confirmed, I'll be in the market for piston rings for 0.5mm oversized pistons. I'm going to put the original pistons back with the new rings since it didn't seem like there was substantial wear on the piston body.
I also believe the vertical striations on the cylinder walls confirm my suspicion of piston slapping (see pictures).

Anyone order piston rings from common motors? https://www.common-motor.com/honda-cb550k-cb550f-piston-rings?gad_source=1&gclid=Cj0KCQjw8--2BhCHARIsAF_w1gwi0konqQ5o-sp4fl8qpc42NBUHie_PPy2F7PUh18EzYuAcEfpGFNQaAo33EALw_wcB

On a separate note, when I got to the pistons, pistons 3 and 4 had a surprisingly larger amount of dirty oil/gas(?) built up on the top surface. Any thoughts as to possible causes?

Thank you again to all for the help! The feedback and expertise on this forum is invaluable.

[Don R]

 Deposits on the pistons and head can be caused by low compression and incomplete combustion.

[calj737]

You don’t want to run 58.5mm pistons with any sized ring in a 59mm bore. The motor will not like it. You’ll damage the pistons, the bores, and blow oil like it’s a Cummins diesel.

[bryanj]

That block has been overbored by 0.5mm and as said you can not just fit oversize rings, you need +0.50 mm oversize piston kits ASSUMING there is zero bore damage, or you need +1.0mm kits and a further rebore. Try cruzinimage in japan for piston kits

[Mkubs]

Deposits on the pistons and head can be caused by low compression and incomplete combustion.

I'd imagine the undersized pistons and rings aren't helping.

You don’t want to run 58.5mm pistons with any sized ring in a 59mm bore. The motor will not like it. You’ll damage the pistons, the bores, and blow oil like it’s a Cummins diesel.

That block has been overbored by 0.5mm and as said you can not just fit oversize rings, you need +0.50 mm oversize piston kits ASSUMING there is zero bore damage, or you need +1.0mm kits and a further rebore. Try cruzinimage in japan for piston kits

As mentioned in an earlier posts, I didn't realize that the cylinders were overboard by 0.5mm. I thought I was putting new pistons and rings in a standard 58.5mm bore.

The pistons I removed (that I thought were original size) were actually already 59mm.
I'm going to measure whether or not the oversized ringson the 59mm pistons are still sufficient or if I'll need new ones, but I'll probably end up getting new ones anyway.