Honda CX 500 Forum banner

1 - 20 of 35 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #1 ·
I'm hoping to receive some confirmation that my issues are stemming from a bad head gasket before I pull things apart and place some orders.

The bike is a relatively new-to-me 1979 CX500D running an old Rae-San ignition system (Raymodule) and stock VB23A carbs w/ Murray's pod filters. The jets are not stamped, but I would bet that it has not been re-jetted for the pods.

The bike starts and idles without issue; however, the right exhaust has a significant enough amount of white smoke (after having run for long enough that normal condensation would have evaporated) to indicate head gasket failure. In addition, the radiator purges maybe a tsp/tbsp of coolant out the bike after shutdown. Beyond those issues that are most likely from a bad gasket, there is also the issue of misfire that occurs mildly at low-to-mid throttle (acceleration hindered), heavily at mid-to-high throttle(rate of acceleration significantly reduced), and minimally at WOT (bike seems to catch again, but there are noticeable white plumes out of the right exhaust). The misfire is also indicated by the significantly cooler right-side primary.

Additional info: I have "cleaned" (Pine-Sol soak, carb cleaner sprayed, and air compressor blown) the carbs, and confirmed the float bowl levels to be right beneath the bowl seam. I have tested (with two different multimeters) the right side aftermarket coil to be at about 5k ohms. The 5k ohm NGK plug cap tested at 4.5k ohms. Valve clearances are within spec. I do not see any green specs on the right side spark plug, but it is noticeably wet. There also appears to be some steam out of the right-side cylinder upon spark plug removal. I do not see any froth in the oil. Allergies mean that I can't quite smell if the smoke smells sweet, but I know it does not smell like burning oil smoke.

I am pretty sure I have a bad head gasket but didn't want to pull the trigger on parts without another opinion. I think the combination of the white smoke and the misfire has me a bit confused as to whether or not this is all the result of a bad gasket, or if it is a clogged jet/hiccuping ignition system thrown into the mix; I'd appreciate any insight. Thanks!
 

·
Registered
1982 gl500
Joined
·
60 Posts
Usually white smoke indicates coolant in the combustion chamber, blue smoke is oil. Rich tune tends to cause the spark plug to get fouled. Almost nothing else causes smoke. You can do a leakdown test to confirm things if you want to get ahold of a leakdown tester - it plugs into an air compressor and injects a limited pressure air into the engine, in this case I would expect it to cause bubbles in the radiator. Usually a blown head gasket will have some obvious damage to it, once you get the heads off inspect the gaskets closely.

There is also a slight chance it is a crack somewhere, but I don't know if that happens with these engines, some heads are more prone to cracking than others and these look pretty robust - lots of extra aluminum. If nothing is obvious when inspecting then you can have a shop magnaflux the heads to confirm they aren't cracked.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #3 ·
Nice and succinct, thank you. I will do a leak-down test for peace of mind and plan on ordering head gaskets.
 

·
Registered
1982 CX500C
Joined
·
41 Posts
Certainly a leak down test will be the best way to diagnose it, but you can also check to see if there’s coolant in the oil. The oil will be milky in color if it’s contaminated.

FYI there are several possibilities for head gasket failure. As an auto mechanic the most common one I’ve seen is lack of proper cooling system maintenance which leads to either restrictions in the cooling system (ultimately causing lack of flow) or electrolysis which deteriorates the block and heads. Do your best to separate the heads while keeping the gasket in tact to determine where it failed and why.

Before assembly make sure to chase all threads for the head bolts or studs/nuts and clean with compressed air.

I’d recommend getting a service manual as well.
 

·
Super Moderator
Joined
·
22,316 Posts
OEM CX head gaskets don't do 'intact' when coming off. In fact, they're complete mongrels.

I remove the two small headbolts, loosen the large ones about 7or 8 turns, set the cylinder to TDC compression stroke and blow the head off with the leakdown tester.
 

·
Super Moderator
Joined
·
4,677 Posts
Make sure to use good head gaskets; either OEM Honda or from Murray's Carbs.https://murrayscarbs.com/product/cx-gl-500-head-gasket-x-2/
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #7 ·
Thanks for the warning CXPHREAK.

I’ve got two of Joe Hovel’s gaskets on order. Well, four actually, my other CX has oil seeping out of the left head, so I’m going to learn from this bike and then take care of that one. I also have 12 (8 for pipes from thermo housing, 4 for elbows) coolant o-rings and 4 new head dowel pins on the way. I will post pictures of the head gasket failure points.
 

·
Super Moderator
Joined
·
22,316 Posts
I use Joes headgaskets. They're good but be sure to give them retorques until they cease to move as they're quite compressable.

If you don't have Joes schedule here's mine.

Warm up bike in the shed while burping cooling system. Leave bike to cool overnight and retorque before starting again. Don't forget to adjust the valve clearances each retorque as the clearances close up as the head moves down as these are pushrod engines.

Then 100 miles, 250, 500 and by then you should be done.
 

·
Registered
1982 CX500C
Joined
·
41 Posts
OEM CX head gaskets don't do 'intact' when coming off. In fact, they're complete mongrels.

I remove the two small headbolts, loosen the large ones about 7or 8 turns, set the cylinder to TDC compression stroke and blow the head off with the leakdown tester.
I figured as much but thought I’d encourage the OP to try anyway.

I appreciate your removal procedure though - ever forget to leave the bolts in and accidentally send a head flying?:D
 

·
Registered
Joined
·
114 Posts
does that actually preserve the head gaskets or just make removal easier?
 

·
Super Moderator
Joined
·
22,316 Posts
Makes head removal easier.

You'll be lucky if you get one of these gaskets off clean by any method. In fact, if you do, it is an aftermarket gasket kit replacement.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #13 ·
Makes head removal easier.

You'll be lucky if you get one of these gaskets off clean by any method. In fact, if you do, it is an aftermarket gasket kit replacement.
Do you have any preferred scraping methods (probably a plastic scraper)? Soak them in anything prior to scraping?
 

·
Super Moderator
Joined
·
22,316 Posts
I use a small steel scraper - very carefully and will soak the gasket with acrylic paint thinner ahead of my scraper as I go to soften it a little. There are commercial gasket strippers too. With those you likely can use a plastic frost scraper.
 

·
Super Moderator
Joined
·
4,677 Posts
A sharpening stone is good for final cleanup.
 

·
Registered
1982 CX500C
Joined
·
41 Posts
Soaking it in penetrating oil also works.

Soft bladed scraper to clean the bulk of it followed by fine wool mesh or scotch brite pad for the smaller spots hard to remove. Spray a clean shop towel with brake or carb cleaner and wipe down the sealing surfaces before installation.
 

·
Super Moderator
'84 CX650E that is evolving into a GL500
Joined
·
16,291 Posts
The Honda Common Service Manual says to remove the big pieces and then clean & smooth the surfaces with a stone...
Use of solvents can damage the paint so if you feel the need to do so be very careful.
 

·
Registered
1982 gl500
Joined
·
60 Posts
Be careful not to get much junk down in between the pistons and the cylinder walls, some grit in there will scratch the cylinders right up if not removed. If you already started cleaning, you can turn the engine over a couple times slowly, cleaning the cylinder walls when at bottom dead center. Don't use air or cleaner for this, it can make dirt harder to remove. If it isn't too late, do all the cleaning on each side with the piston at the bottom and a rag stuffed in above it as protection.
 
  • Like
Reactions: rounders

·
Super Moderator
'84 CX650E that is evolving into a GL500
Joined
·
16,291 Posts
Good point. I usually set the piston a bit below 1/2 way down and wad some toilet paper above it before I start cleaning the mating surfaces and put wads in all of the openings (I twist some into a rope for the coolant passages), then when it is clean I remove everything, wipe out the cylinder, run the piston to BDC and wipe out the inevitable ring of garbage from where the piston was when I was cleaning the mating surfaces.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #20 ·
I appreciate all of the input thus far, will be keeping all of it in mind. I plan to begin disassembly on the first bike tomorrow and start on the gasket removal. While I’m in there, I was planning on replacing all of the valve stem seals. I was planning on going with Genuine seals, but for 16 seals across two bikes, it adds up. If doing the seals is necessary (is it?), is this one of those parts where the aftermarket will suffice or the Genuine is vital?
 
1 - 20 of 35 Posts
Top