Lost Compression

[moore020]

Was riding my bike in snow and it died on me. Took all the plastics off and got the spark plug and found that I dont have any compression. It was never smoking or anything of the sort. My wife was riding it and I think she had it overrevved. What are some of the possible causes? What are the easiest tests to and repair attempts?

[PaRedneckRiders]

Well did you do a compression test.
I could be worn rings or a worn bore.(no longer round)

So either new rings might fix it if not you will prob need a new bore piston and rings.

If you did a comp. test what were the numbers on it? and do you have a stock cam?

[mlabarca240]

It died all of the sudden? Did you notice it wasnt as powerful as usual or if it was blowing smoke like crazy?

[PaRedneckRiders]

Originally posted by mlabarca240
It died all of the sudden? Did you notice it wasnt as powerful as usual or if it was blowing smoke like crazy? '
Ya if it was smoking a bluish white color it means it was burning oil which would most likely mean worn rings.

[crownandmonster]

Originally posted by moore020
Was riding my bike in snow and it died on me. Took all the plastics off and got the spark plug and found that I dont have any compression. It was never smoking or anything of the sort. My wife was riding it and I think she had it overrevved. What are some of the possible causes? What are the easiest tests to and repair attempts?


I'm reading this as you took the spark plug out and didn't have compression..does this mean you did a compression test or just turned it over with the plug out. It won't have compression with the spark plug taken out.

[moore020]

It wasn't blowing any smoke at all. It was rebuilt last winter and went through an extensive break in period. I did not notice it losing any power at all prior to it dying. I did not do an actual compression test, we removed the spark plug and stuck a finger obver the hold to test for compression. In first gear it had some resistance to being pushed, but it had very little resistance to being pushed in second.

[exrider12]

check your electrical. Maybe something got wet. This doesnt sound like an engine issue to me.

[moore020]

It will try to turn over but there is no "normal" turnover sound, sounds more like a high whir.

[crownandmonster]

So the starter is turning, but the crank is not?

[moore020]

I honestly dont know, but that sounds like a very plausible idea. Any ideas on what may cause this or how hard it would be to investigate it?

[crownandmonster]

Most people can tell by sound, um I guess you could take the big plug out of the side case (right above the shifter) and then lightly bump the starter and see if the crank is moving.

[CJM]

Id check and see if its actually turning.

Friend of mine had a similar issue. Thing just died, we drove hours to get to a spot and he made it 100ft. Turned out his timing chain tensioner busted. Replaced it, was fine and blew again, chain was stretched. Replaced chain, guides and tensioner and no issues. It sounded like a glup glup noise when it tried to turn over cause it jumped time slightly and it wouldnt start.

If the starter clutch died (which wouldnt cause it to die while moving imho) you would get a whirring noise and the engine wouldnt be turning over at all I would think.

[450Rida]

Originally posted by moore020
I honestly dont know, but that sounds like a very plausible idea. Any ideas on what may cause this or how hard it would be to investigate it?

do a compression test and a leak down test. evrything u need to know on how to do them and what it should be at will be in the service manual. you can pick up both tools from princess auto or any other auto store for a reasonable price. if it was "whineing" start by checkin the starter solenoid, then the starter. check the carb aswell, water or other foriegn debris will cause it to die, and have low compression if the slide stuck open. and like CJM said if your cam chain stretched it would retard the cam timing causing it to die, and give you low compression readings. if it stretched chances are you had valve to piston contact and can add to an expensive repair.

[moore020]

Thanks for the reply sounds like I have some work to do!

[moore020]

Winner Winner Chicken Dinner to CJM, tore it apart yesterday and it was a broken cam chain. A couple of questions for you guys now. I am reading it is cool to go with a CRF 450R cam chain, is this right? Also, If I go with the CRF Cam Chain, do I need to get new sprockets and guides? I am on somewhat of a limited budget and want to get it back together for spring riding.

[CJM]

Thank you, thank you! :D

Only way to tell if you need guides is to open it up and look at them. They look worn you replace them.

You want a CRF chain, I used an 02 but I think 02-04 is the same part #.

The sprockets are probably fine, inspect them for damage but I doubt they will have any.

Buy the spring loaded tensioner while your at it and play if safe, might be fine but I wouldnt want to find out it isnt later.

[moore020]

How much and where did you get your CRF chain at? Also, are you referring to the Cam Chain tensioner that has a screw on the top and bottom and located on the pipeside of the motor?

[CJM]

I bought mine from service honda, but you can find it on ebay, bike bandit, rocky mtn, mr cycles. Anywhere really that sells OEM parts. Your local dealer might be ok too, I dont have one nearby so I buy all my stuff online.

Yes, the auto tensioner if the thing on the right side of the cylinder with 2 bolts and a screw that caps over it. Its worth replacing if your replacing everything else.

In total expect to spend about 120-150 for everything, the guides are rather costly at about 30-50 ea, the tensioner is 60 and the chain is 45-50 bucks. BUT when everythings new, chances of stuff wearing out or failing is GONE.

[BenHonda400ex]

Originally posted by CJM
I bought mine from service honda, but you can find it on ebay, bike bandit, rocky mtn, mr cycles. Anywhere really that sells OEM parts. Your local dealer might be ok too, I dont have one nearby so I buy all my stuff online.

Yes, the auto tensioner if the thing on the right side of the cylinder with 2 bolts and a screw that caps over it. Its worth replacing if your replacing everything else.

In total expect to spend about 120-150 for everything, the guides are rather costly at about 30-50 ea, the tensioner is 60 and the chain is 45-50 bucks. BUT when everythings new, chances of stuff wearing out or failing is GONE. Are you like the god of all Honda 400ex's? haha

[CJM]

Originally posted by BenHonda400ex
Are you like the god of all Honda 400ex's? haha

no, but ive had the topend apart more times than I can count. Not mine btw,my friend bought a bum 400 and we kept having issues. I can have the entire top apart and redone in like an hour or so.

it also helps this same exact situation happened to said buddy as well.

also helps im a mechanic by trade among other things.

jack of all trades, master of none?

[moore020]

Thanks for all of the information, I appreciate it. I will do the repair and let you guys know how it turns out.