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Hep with engine rebuild
Hep with engine rebuild
This is my first attempt at rebuilding an engine. I bought a '65 cb77 and the right side compression is really low. I dug into the top end and found a few things that are suspect but I have no experience here. I took some picture to see if someone could help identify whats in there.
The first pic shows the hole where the oil drains out of the head. The valves look dirty, and I really can't tell thier condition from the pic. Not sure what you're trying to show in the third pic. What are your concerns?
Davo
Davo
davomoto
64 CB77
63-7 CB77 Cafe'
67 CL77
64 CL72
66 CL77 big bore flat tracker
Many others!
64 CB77
63-7 CB77 Cafe'
67 CL77
64 CL72
66 CL77 big bore flat tracker
Many others!
In the third pic, the intake valve is sticking out. But that's on the left side, where compression was fine. Not sure if that's normal or not.
Second pic shows one of the valves, right side, is a little dirty.
I've never done this before so not sure what to look for, what's normal, etc.
Anything else I should be looking for? How can I test to see if it's a ring and if I need to replace those, do I also need to have the cylinders bored?
Thanks, just trying to learn
Second pic shows one of the valves, right side, is a little dirty.
I've never done this before so not sure what to look for, what's normal, etc.
Anything else I should be looking for? How can I test to see if it's a ring and if I need to replace those, do I also need to have the cylinders bored?
Thanks, just trying to learn
Hi skisurf,
Well there's a couple of things that you probably should have done before disassembling the engine. If compression was low, the thing to do is a leak check or differential compression check. Basically you hook up compressed air to the cylinder while that cylinder is at TDC of compression stroke. Then listen for the air leak. If compressions are bad you will hear air coming from the intake, (leaking by intake valve) exhaust pipe (leaking exhaust valve-more common than intake) or the breather tube or oil filler (leaky rings). There is more info out there on how to perform a diff comp check. If it's a leak by one of the valves, it will probably require more attention, especially if it's an exhaust valve. If it's leaky rings, you have more options. Look into the cylinder through the plug hole and check the condition of the cylinder. Also, say you know the bike has been sitting for quite a while. Then I would probably just ride with some additives in the oil and gas (like Seafoam or Marvel) and see if it clears up-check it often if you go this route.
Now that you're at this point, put the spark plugs back into the head, turn the head upside down and fill the dome with gas making sure the valves are covered (valves closed). After a while look for any gas seepage in the exhaust and intake ports.
The pic of your valves looks as though they are not seating very well.
As far as rings go, you may or may not have to do anything. Since you have the head off you might as well pull the cylinders and look at the pistons and rings. Check back here with what you find. Sometimes the rings break. Sometimes they get stuck in the grooves if the bike hasn't been started for a long time. Sometimes the cylinders get glazed to a point where the rings just don't seal as they should anymore.
Anyways, this is good because now you get to learn all about your new bike and engine.
Jethro
Well there's a couple of things that you probably should have done before disassembling the engine. If compression was low, the thing to do is a leak check or differential compression check. Basically you hook up compressed air to the cylinder while that cylinder is at TDC of compression stroke. Then listen for the air leak. If compressions are bad you will hear air coming from the intake, (leaking by intake valve) exhaust pipe (leaking exhaust valve-more common than intake) or the breather tube or oil filler (leaky rings). There is more info out there on how to perform a diff comp check. If it's a leak by one of the valves, it will probably require more attention, especially if it's an exhaust valve. If it's leaky rings, you have more options. Look into the cylinder through the plug hole and check the condition of the cylinder. Also, say you know the bike has been sitting for quite a while. Then I would probably just ride with some additives in the oil and gas (like Seafoam or Marvel) and see if it clears up-check it often if you go this route.
Now that you're at this point, put the spark plugs back into the head, turn the head upside down and fill the dome with gas making sure the valves are covered (valves closed). After a while look for any gas seepage in the exhaust and intake ports.
The pic of your valves looks as though they are not seating very well.
As far as rings go, you may or may not have to do anything. Since you have the head off you might as well pull the cylinders and look at the pistons and rings. Check back here with what you find. Sometimes the rings break. Sometimes they get stuck in the grooves if the bike hasn't been started for a long time. Sometimes the cylinders get glazed to a point where the rings just don't seal as they should anymore.
Anyways, this is good because now you get to learn all about your new bike and engine.
Jethro
Last edited by Jethro on Sat Nov 12, 2011 1:37 am, edited 1 time in total.