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Discussion Starter #1
Hello,
I got a good deal ($400) on a CM400E which I'm planning to pick up (assuming the electrical works, which the seller says it does) this week. It needs a head gasket and before I finalize the sale I want to know what I should look for that would be a red flag for a ridiculous or expensive repair. I have already sent requests for quotes to 2 local machine shops to see if the head is level and if not to level it. Other than a warped head, what might be wrong to cause a head gasket failure and should it be a deal breaker?
Thanks!
 

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Head gasket failure is pretty rare and a warped head even more so. Usual problems in that area are the 2 rubber seals between the head and cylinder and the valve cover gasket/grommets.
I'd check compression, spec is 185 but low to 155 or so will be ok. Other than that you're looking at the basic overall condition and if everything is there that should be.
 

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Discussion Starter #3
So do you think there are any more serious underlying problems that show a failed head gasket as a symptom, or should I just replace the gasket, change the oil and not worry about it?
 

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Just a second thought here as beyond the motor work how is the rest of the bike? Tires have date codes and after 5 years even if the tread looks good they should be replaced. The battery and fork seals are areas to check and brake pads for wear. The carbs will need cleaning if the bike has sat for a few years and how is the interior of the gas tank as far as rusty interior.
How mechanically inclined are you in removing a head and cam realignment and possibly the barrels to avoid seepage at the cases once the tension is removed by taking off the head.

This maybe a case of $400 turning into a $1400 repair and so you might be better off buying a $1200 bike that is running and has has some of the work/parts above replaced already by the PO.
 

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Discussion Starter #5
The bike has almost brand new tires, a new battery and has just had all of the engine seals other than the head gasket redone. It only needs the head gasket and one fork seal to be perfect.
 

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About the only likely "underlying problem" would be loose head bolts and that will be corrected during the replacement. Head gasket replacement is fairly straight forward and not a bad way to get your feet wet if you're wanting to learn about wrenching.

Do you have the factory service manual?
 

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Discussion Starter #7
I'm ordering an Athena gasket set and fork seals from bike bandit and picking up a used clymer manual on ebay. While I have it apart I'm going to check the valve lash too probably. This is my first serious in-engine work but my dad and my uncle are really good around engines in case I get stuck.
 

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Maybe I'm overthinking this but I talked to an older guy who does a lot of wrenching (to be fair, mostly on British bikes) and he said that those 80s Hondas are bulletproof so if it needs a head gasket something must really be wrong to cause it. That didn't sound quite right to me so I decided to do some more research before blowing off the seller or committing to the sale.
 
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