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Discussion Starter #1
The engine I was building over lockdown has failed to start. I've not run a compression test yet but I'm fairly sure that's the problem.

Can I re-use the head gaskets and rings if necessary? It hasn't run so it's not been subject to heat or revs above what the starter spins it at. I don't have alot of money and I've spent a fair bit on Honda head gaskets, new rings and bearings. Re-usable after disassembly and evaluation?
 

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Discussion Starter #3
Rings yes. Head gaskets likely not.

Take a compression test before proceeding because I doubt if these things will be your issue.
I'm hoping not, Mark. The flame that came out of the exhaust from putting a little petrol in the balancing port wasn't very forceful. It was more like a mild "whoof" than a pop. I've got too much money invested, money I don't really have, to waste on head gaskets and stuff.
 

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1978 CX500 "The Grub", '83 GL650, '82 GL500 Project "AdventureWing", '79 CX500C, '78 CX500 Scrambler
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If you got fire in the exhaust, I'd suspect ignition timing/swapped coil leads.
Maybe you already said you've verified that.
 

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Discussion Starter #5
If you got fire in the exhaust, I'd suspect ignition timing/swapped coil leads.
Maybe you already said you've verified that.
The thing is Randall I just kind of dropped the old engine out, running very well but knocking a bit, and put the rebuilt one in. I didn't mess with the carbs, coils or coil wires. In theory ( I know) it should have fired right up as nothing was really disturbed. I had the carbs and ignition spot on before removing the engine in hopes that I wouldn't have to fuss with such things. I'm no stranger to removing and installing CX engines, but it IS possible I missed something I guess. Waiting for my compression tester to arrive and for the garage to a be a little bit warmer!
 

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1978 CX500 "The Grub", '83 GL650, '82 GL500 Project "AdventureWing", '79 CX500C, '78 CX500 Scrambler
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Did you paint this engine and/or mounting hardware? Poor ground contact is the only other idea that comes to mind.
 

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If you can do a leakdown test as well as a compression test.

You really don't want to pull the engine down due to low compression only to find you had a valve sealing problem.

+ what Randall said. I always file mounting points to bare metal for this reason.

A rebuilt motor can have low compression until the rings bed. But anything north of 100 PSI should see it start.
 

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Discussion Starter #8
Did you paint this engine and/or mounting hardware? Poor ground contact is the only other idea that comes to mind.
No paint. I'm dreading the results of the compression test. I'll be happy if it's within limits, not so much if it fails. That means I've not done the rings right. Maybe didn't de-glaze the cylinders enough. Maybe didn't lap the valves enough. Frustrating to say the least.
 

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Discussion Starter #9
If you can do a leakdown test as well as a compression test.

You really don't want to pull the engine down due to low compression only to find you had a valve sealing problem.

+ what Randall said. I always file mounting points to bare metal for this reason.

A rebuilt motor can have low compression until the rings bed. But anything north of 100 PSI should see it start.
I don't have a leakdown tester. I'm waiting for my cheap ebay compression tester. I do have a small portable air compressor for tires (tyres) though. Don't know what it's max pressure is though.
 

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Corrosion on valve seats and faces can be an issue with motors that have been laid up for a while. Sometimes this will sort itself once the motor is running if it is just crap caught in the sealing area.

My leakdown tester is just a metal spark plug body, a piece of 1/2" tube and a compressor line fitting.

Mine was made for me by a friend and is silver soldered. It could also be welded. Can you do either?

Any photos of your cam chain when it was set up?
 

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Discussion Starter #11
Corrosion on valve seats and faces can be an issue with motors that have been laid up for a while. Sometimes this will sort itself once the motor is running if it is just crap caught in the sealing area.

My leakdown tester is just a metal spark plug body, a piece of 1/2" tube and a compressor line fitting.

Mine was made for me by a friend and is silver soldered. It could also be welded. Can you do either?

Any photos of your cam chain when it was set up?
I've lapped the valves with coarse, then fine compound. Shouldn't be an issue but doesn't mean it isn't. I don't have the means to weld or solder. I have a soldering gun, though I'm thinking you mean soldering with a torch?
 

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Discussion Starter #13
If you've lapped them I doubt this is the issue. If they leak it will be by a small amount that shouldn't prevent a start.
Is there a picture available of what your leakdown tester should look like? I may have to fashion one.
 

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I made mine from an old spark plug with the innards removed and a pipe nipple epoxy metaled into place. An air compressor fitting screwed onto the end of the pipe nipple. No welding involved.
 
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Hi
Just to make sure you open the throttle all the way when you do the compression test
not opening the throttle will give you a low compression reading
also drain the float bowels before you do the compression test.You don't want to wash the cylinder's down Make sure you ground the spark plugs. Not done it can kill the CDI box
Seen two people do that when they did a compression test
Good luck

TLD
 

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How fresh is your fuel? Did you drain the carbs?
 

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Discussion Starter #18

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Discussion Starter #19
Hi
Just to make sure you open the throttle all the way when you do the compression test
not opening the throttle will give you a low compression reading
also drain the float bowels before you do the compression test.You don't want to wash the cylinder's down Make sure you ground the spark plugs. Not done it can kill the CDI box
Seen two people do that when they did a compression test
Good luck

TLD
Good advice. No carbs on it at the moment, I took them off. No exhaust either. Tape the plugs to the front hanger bolts?
 
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