Topic: To Ring or Not to Ring (CB550f question)

[StreetSpirit]

Hello all,

I'm starting a resto/cafe conversion on a 1977 cb550f that I recently acquired, and I'm chasing my tail regarding piston rings. 

I've only had it running on starter fluid, but it didn't smoke or otherwise misbehave.  Previous owner said it was running smooth and strong before sitting a couple months, so the engine is probably ok...  A compression test (cold with an automotive tester) showed comp readings between 125 and 135 psi, which seems to be on the low side, but that may be a function of a cold motor. 

Basically, I'm trying to decide if I leave well enough alone or rip into the top end.  I know fresh rings are a selling point, particularly on a bike with 34k on the clock, and it would let me lap the valves and maybe mill/port the head while I'm in the motor.  However, I've never done it before and it's a bit daunting.  I'm also wondering if anybody has advice for me one way or the other.  If I do tear it down, what other items should I be replacing?  Any checks I should perform?  Also, I've seen a few people swapping in a 650 cam and I'm wondering if the mod is worth the trouble or if I should be looking at other options for a reliable boost in output.

Thanks for your help.

[OldSchool_IsCool]

Absolute values of a compression test are somewhat meaningless unless you are using the same tester that Honda uses. There are just too many variables between testers.

What is significant is that all cyl are within 10% of each other. That's generally a characteristic of a solid engine.

I'd run 'er for a few hundred more miles and test 'er again. This time hot. Then do a second comp test with engine hot and a cc of oil in the cyl (wet test). If the dry & wet numbers continue to be within 10%, then no reason to crack 'er open.

Now, if she develops an intollerable oil leak and ur intent is to sell, then you may need to. At which point, you will be replacing all gaskets & seals right on down to the base. A new cam chain & tensioner too since ur in there. Valve seals if the wet/dry indicates a need. Otherwise a valve lapping should do.

[StreetSpirit]

Well, the long range plan is definitely to sell the bike, but probably not immediately.

If it were a lower mileage bike I wouldn't even think twice, I'd just run it, but 34k is getting up there for the original rings.

[OldSchool_IsCool]

Well, the long range plan is definitely to sell the bike, but probably not immediately.

If it were a lower mileage bike I wouldn't even think twice, I'd just run it, but 34k is getting up there for the original rings.

Maybe on some brands and if ridden hard or poorly maintained.  When I opened my '77 550K3 with 36K on the clocks to fix an oil leak, the cylinder walls still had their honing marks.  Rings were withing spec too.  I went ahead and put in new rings and rehoned but only cuz I had already bought them.  I oiled the old rings and wrapped them in plastic just in case my grandchild needs them when they rebuild the bike and the needed rings are no longer available ;-)

[TwoTired]

Well, the long range plan is definitely to sell the bike, but probably not immediately.

For profit?

If it were a lower mileage bike I wouldn't even think twice, I'd just run it, but 34k is getting up there for the original rings.

Sounds like you've already made up your mind and just want us to pat your back.
But, it really depends entirely on how those miles were put on, and how well maintained the bike was kept during it's life.
34K @ 9K RPM and dirty oil will certainly wear out the rings.  Normal use and clean oil, probably not.

Check out the Engine FAQ regarding your compression test assessment.  The numbers look fine to me.  And if you used an automotive tester, the numbers will almost certainly be lower than what Honda noted with the correct low volume compression gauge.

You could also use a leak down tester to get a more accurate picture, and it will also tell you where the pressure is being lost.

[StreetSpirit]

Yeah, maybe this is just group therapy...

Also, yes I do ultimately attempt to profit from building, though I genuinely enjoy tinkering and riding old bikes just for the hell of it. 

I'm rather unemployed at the moment, and mobile wrenching and rebuilds have been keeping me afloat while I hunt for that elusive career thing.  Beats working at Starbucks, right? 

Anyway, this is the oldest and most expensive ($500) bike rebuild I've undertaken, and I want to do it right.  Profit means not doing work that doesn't need doing, but if $50 rings and 5 hours of work means $500 at resale time, that's a good investment for me. 

I'm probably going to pull the head regardless and have a looksee. 

[OldSchool_IsCool]

If you pull the head, then you'll be replacing gaskets down to the base gasket under the cyl block.  And since you're into it that far...

Bad compression, a slapping cam chain or a major oil leak are good reasons to crack into 'er.  Opening 'er up just for tourism could add $200+ to your rebuild cost and would not likely be recoverable. 

[TwoTired]

I'm probably going to pull the head regardless and have a looksee.

Then you are eating into your profit margin for recreational purposes.  About $100 just for gaskets.
OK with me, your time, your money.
Pay attention to rocker alignment while putting on the cam cover.  Lot's have bent valves upon reassembly, turning a perfectly good engine into a money pit or boat anchor.
Best to use the Honda manual and heed their instructions.  Easy to fail without it.

[Gordon]

You're in for a surprise if you think new rings are going to increase the value of the bike by $500.  In fact, if the engine is already running well in its current state, putting on new parts that aren't needed may not get you any more money at all when selling. 

[Stev-o]

I agree with Gordon. Replacing rings at 34K may actually turn off informed buyers, a maintained bike should not need rings yet.