fredtman
New Member
I'm considering buying a 1981 Honda 400cmf Hondmatic that has 11,000 miles. What kind of issues should I look out for? What routine maintenance is required for this bike?
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What Should I watch out for when buying a CM400 Hondamatic?
- Thread starter fredtman
- Start date
Compression check. Done with throttle held wide open, both plugs removed and cranked until gauge stops rising. Spec is 185 +/-14 psi. Below 155 will present problems in the near future.
Check for obvious oil leaks, general condition. If it starts will it idle after hot.
Basic maintenance is pretty simple stuff like valve adjust every 6K, oil/filter changes every 3K, drive chain lube/adjust as needed, etc. Timing is fixed and it's a CDI ignition so no points
Check for obvious oil leaks, general condition. If it starts will it idle after hot.
Basic maintenance is pretty simple stuff like valve adjust every 6K, oil/filter changes every 3K, drive chain lube/adjust as needed, etc. Timing is fixed and it's a CDI ignition so no points
Boosted
Veteran Member
..brake fluid refreshment/renewal every year, two, or three dependent upon type and number of heat cycles/exposure to hot sun while parked...
battery tending
tire air pressures...
..Their intake manifolds or "insulators" that connect the carbs to the motor are different (smaller bore) than those used on the manually shifted bikes AND they're hard to find when needing replacement, along with another part(s) I've forgotten specifically... the "change switch" or "neutral safety switch" ??
Matic Master @Maraakate will know more of what I'm mentioning...
battery tending
tire air pressures...
..Their intake manifolds or "insulators" that connect the carbs to the motor are different (smaller bore) than those used on the manually shifted bikes AND they're hard to find when needing replacement, along with another part(s) I've forgotten specifically... the "change switch" or "neutral safety switch" ??
Matic Master @Maraakate will know more of what I'm mentioning...
Maraakate
Veteran Member
The intake manifolds, yes. There are no real aftermarket substitutes and when they were sporadically available they only lasted for a couple of years. That "change switch" is hard to find, but if the gear indicator is working then it is there and working fine.
CDI is a problem. Not saying this to get you to buy one from me. If someone is bragging about low miles and low usage that's ironically an issue because the capacitors in the CDI are use it or lose it. NOS CDI is prohibitively expensive, but also a false economy because the dielectric dries out in the capacitors from sitting around doing nothing.
Open the airbox, make sure there isn't a mouse nest in there. Pull the two plugs at the bottom of the airbox to drain any residual junk out of them. They're supposed to get pulled every so often and nobody does it.
Besides compression check for leaks from cylinder head to cylinder after riding it for about 10 minutes. If it's been sitting a long time it's not unusual for it start weeping oil there. There are grommets that go over the dowel pins between those two parts and they dry out and start causing an oil leak. It's not super hard to replace, but if you have little experience in doing so it can be a bit tricky.
Unusually loud noises. Cam chain tension, incredibly loose valves (or their keepers floating around in the head... have seen this before), and incredibly loose balancer chain can cause these problems.
The stock exhaust likes to rot out at the joints. Especially if it saw a lot of short trips and never got the pipes up to full operating temp. Feel under the muffler where it joins to the chamber. If it's pushing a lot of air, then check to see if there's a large rotted out hole.
CDI is a problem. Not saying this to get you to buy one from me. If someone is bragging about low miles and low usage that's ironically an issue because the capacitors in the CDI are use it or lose it. NOS CDI is prohibitively expensive, but also a false economy because the dielectric dries out in the capacitors from sitting around doing nothing.
Open the airbox, make sure there isn't a mouse nest in there. Pull the two plugs at the bottom of the airbox to drain any residual junk out of them. They're supposed to get pulled every so often and nobody does it.
Besides compression check for leaks from cylinder head to cylinder after riding it for about 10 minutes. If it's been sitting a long time it's not unusual for it start weeping oil there. There are grommets that go over the dowel pins between those two parts and they dry out and start causing an oil leak. It's not super hard to replace, but if you have little experience in doing so it can be a bit tricky.
Unusually loud noises. Cam chain tension, incredibly loose valves (or their keepers floating around in the head... have seen this before), and incredibly loose balancer chain can cause these problems.
The stock exhaust likes to rot out at the joints. Especially if it saw a lot of short trips and never got the pipes up to full operating temp. Feel under the muffler where it joins to the chamber. If it's pushing a lot of air, then check to see if there's a large rotted out hole.