Author Topic: i need advise on cb550! (Read 4663 times)

pinnacle · « **on:** April 28, 2009, 05:38:09 PM »

hello my fellow honda men! i did a compression test on my engine before i tear into it for a leaking headgasket and need help interpreting the numbers.I'll start off by telling you guys how i came to the numbers. i started off by running the bike for 10 min to warm it up, i then pulled the spark plug wires off and shut fuel off. I started at cylinder 1 and put the compression tester on it and hit my starter button and turned it over until it didn't climb any higher on the gauge topped off at 75 psi dry then added a teaspoon of oil and repeated and got 90psi. cylinder #2 dry 80psi wet 85. Cylinder #3 is where things get funny because my starter was dead by then and so i kicked it over with the kickstarter until my leg couldn't no more and i got 95psi dry and 105 wet.cylinder #4 with kickstarter again dry 95 psi wet 110 psi. What i don't understand is with the kickstarter i was getting better numbers on the gauge so i went back and did #1 and #2 again with the kickstarter and got 100 psi on #1 and 110 psi on #2 with kickstarter but by this time i had already added oil from previous test. so i am thinking that my method was flawed in some way but in the end with oil in the cylinders the psi numbers were follows 100,110,105,and 110 from cylinder number 1-4. The bike is a 78 cb550 stock motor with pod filters and fairly open exhaust. Please guys chime in and tell me what my next course of action should be and what you can interpret from these numbers as to the state of the engine do i need to rebuild it?

OldSchool_IsCool · « **Reply #1 on:** April 28, 2009, 05:45:33 PM »

Since you didn't get good DRY numbers for #1 & #2, I suggest you run the test again. A couple of revisions to your test method:

Kickstart for all tests. As you found, it is a lot easier to get a consistent kick then it is to get a consistent crank.
You didn't mention the position of your choke & throttle. Make sure both are WIDE OPEN for maximum air flow through the carbs. May even eana pull the pods off during the test.

Post a new set of wet & dry numbers here for wildly contentious opinions on what they mean!

pinnacle · « **Reply #2 on:** April 28, 2009, 05:58:36 PM »

why does the position of the throttle and choke matter if we do not have ignition? and how long do i wait for the oil to burn off on the inside of the cylinders to get good dry numbers?

OldSchool_IsCool · « **Reply #3 on:** April 28, 2009, 06:48:44 PM »

The oil will burn off within a few seconds of warming the engine again. Opening the carbs up will allow the cylinders to suck in the maximum amount of air, thus giving you maximum compression readings.

One other point, if you have the option of a short hose on your compression tester, us it. A long hose will, in effect, add a significant volume to your combustion chamber. If long is all you got, then go with it, but let us know how long it is.

pinnacle · « **Reply #4 on:** April 28, 2009, 07:57:11 PM »

ok so here is my new numbers with new methodology described by old school. Cylinder #1 115 psi dry 123 psi wet, Cylinder #95 psi dry 120 psi wet, cylinder #3 95 psi dry 125 psi wet, cylinder #4 105 psi dry and 120 psi wet. What can i conclude from this i know i have a real nasty head gasket leak i drop every few seconds. Got a new gasket set coming for it. will lapping valves when i got head off to replace seals help any?

OldSchool_IsCool · « **Reply #5 on:** April 28, 2009, 09:34:49 PM »

The large difference between wet/dry readings on #2 & #3 suggest bad rings or scored bores. Valve lap woudn't hurt, you can inspect the valve guides and replace the seals while you are in there. Be sure to keep all valve parts together and return them to their original cylinder.

But like I said before, prepare to wildly contentious opinions!

pinnacle · « **Reply #6 on:** April 28, 2009, 09:41:09 PM »

if it is bad rings where can i get new ones and if it is scored bores what can i do or should i do anything the bike has 43000 km on it should i look for a spare motor and rebuild it instead?

TwoTired · « **Reply #7 on:** April 28, 2009, 10:26:25 PM »

The 550 combustion chamber is about 15cc, and a teaspoon of oil is 5cc which is not compressible.
You are only supposed to put a squirt of oil in the chamber, enough to make a temporary seal of the piston rings, not alter the compression ratio. Raising the comp ratio will make the numbers quite a bit larger even if the rings seal perfectly.

http://forums.sohc4.net/index.php?topic=369.msg476032#msg476032

pinnacle · « **Reply #8 on:** April 29, 2009, 06:48:13 PM »

Alright so i brought a snapon leak down tester from work and thought i would check cylinders out because as two tired mentioned the method on the compression test may have flaws if not done properly. So here is what i did i hooked up the tester starting at #1 at tdc of the compression stroke and set the pressure to 90psi on the tester and on the second gauge it shows a green area for 20-30% low ,a yellow for 40-60% moderate, and red for 70-100% high cylinder leakage as i hooked up the pressure to the cylinders they all stayed put and when i put my ear to the motor with a stethoscope i can hear a little hiising coming from the exhaust valves on all cylinders but no substantial loss in pressure. May i conclude that my rings are fine and that my valves have possibly some carbon build up that is not allowing them to seal properly and that my leaking headgasket may be leaking inwards aswell explaining the smoke in the tail pipe? sombody tell me something please!

pinnacle · « **Reply #9 on:** April 29, 2009, 08:43:58 PM »

can someone take a boo and see what you think

OldSchool_IsCool · « **Reply #10 on:** April 29, 2009, 08:47:02 PM »

I've never done a leakdown test, so I can't help. Is there anyone at your shop that would know how to interpret the readings?

TwoTired · « **Reply #11 on:** April 29, 2009, 10:20:29 PM »

I don't understand your measurement data. A leak down tester has two gauges, one tells what is applied to the cylinder and the other what the cylinder maintains. It's the difference of these readings that indicates cylinder health. Then you can listen for where the leaks makes noise.

How much pressure did you lose?

You are supposed to do this test hot, as well, btw.

Cheers,

pinnacle · « **Reply #12 on:** April 29, 2009, 11:44:50 PM »

i took the bike out for a 15 min rip so it was warmed up as far as how much pressure i lost i was not losing any it maintained pressure i applied 90psi and it stayed there needle was not moving so i put my ear to the cylinders and heard some hissing from exhaust valves but very faintly

TwoTired · « **Reply #13 on:** April 30, 2009, 12:32:13 AM »

Then it sounds like your engine mechanicals are fine now. The oil leak so bad you want to tear into a perfectly good motor? You'll have to go down to the base gasket, you know, pull the jugs off the pistons. And risk bending valves when you put the cylinder cover back on.

New oil orings are that important to you?

Cheers,

pinnacle · « **Reply #14 on:** April 30, 2009, 11:45:18 AM »

quite the opposite i'm not eager to tear into a good motor but the oil leak is bad it leaksa drop every couple seconds and drips onto the exhaust causing alot of smoke.I rolleda paper towel up and put it between the fins but still coming out so at the very least i want to do the top gaskets and may clean up head and paint afterwards.

TwoTired · « **Reply #15 on:** April 30, 2009, 12:40:50 PM »

Have you determined just where it is leaking from?
May not have to go down to the head gasket. Might be able to get at the leaking bits under the cylinder cover.

Cheers,

OldSchool_IsCool · « **Reply #16 on:** April 30, 2009, 03:36:16 PM »

Double check that it is the head gasket. To do this, wash the engine while cold. Let it dry. Spray foot powder on the suspect area. when you next run the engine, the white powder will turn black as oil leaks out.

Sealing rubbers may be the true source of the leak. To change those, you only need to disassemble the engine down to the head cover. Cam shaft doesn't even need to come out.

pinnacle · « **Reply #17 on:** April 30, 2009, 04:32:13 PM »

are you refering to the o-rings that seal around the oil galleries or am i misunderstanding you.as far as i can tell the oil is coming from near cylinder#1 and runs all along under the head pipes that could be wind driving the oil that way but in the garage if i watch i can see the oil dribble out of the left front corner of head i'm open to suggestios i would like to remove head to clean up and replace valve seals aswell as lap valves to get rid of any carbon around sealing edges.

OldSchool_IsCool · « **Reply #18 on:** April 30, 2009, 06:28:56 PM »

The sealing rubbers are #14 in this image. They cover the head nuts which are inside those 6 holes you see there in the head block. There are 4 holes in the rear and 2 up front between the recesses for the spark plugs. Oil seeping through these can follow the fins to the outside edge.

I don't know for sure these are you problem, but they can be changed without taking the head off. If you want to lap the valves, then you will commit yourself to replacing all gaskets and o-rings from the base gasket on up. Not a hard job, but like TT implied, why crack into a good engine if it can be avoided?

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Author Topic: i need advise on cb550! (Read 4663 times)