Honds Fourtrax 300
 

Hey guys i purchased a Honda Fourtrax 300 recently cause it wont run, i did a compression test and go 90 psi . I checked valve clearance and was in spec at .006 in , so then i checked the decompression lever at tdc and its not holding valve open. I have been having a hard time finding a service manual for this bike, i believe its in the 90's. Im thinking maybe rings are gone and it needs a top end... thcd for any info and help.

Super-common and excellent quad, the 88-2000 TRX300FW. It came in 2WD or full-time 4x4.

Service manuals and parts are cheap and common on eBay. Namura piston/ring kits work well.

I have had 3, and one is my longest-term ownership of any ATV. A 1996, which I have owned for nearly 8y, after
rescuing it from extensive abuse.

It may fix right up with just new rings. Pop the head and look to see if decomp lever is not causing a problem. You might
want to first pressurize the plug hole to determine if your lack of compression is thru rings or valves.

thxs for the reply, i was playing with the bike today and i adjusted the valves just to be certain and now i have 150psi... im geting blow back throught the carb now so i wonder if timing is out.

What mark is the one to use for TDC , the I I or the ---I mark..

Well i dug into motor and found timing chains is very loose and tensioner is out all the way and it jumped timing. There is some damage to the valve cover and head where the one end of the cam sits on. So i will share some pics an dlet me know what you think im looking at replacing... thxs
https://cimg9.ibsrv.net/gimg/atvconn...4a4ac80bb8.jpg
https://cimg5.ibsrv.net/gimg/atvconn...03048310d2.jpg

So i looked more into motor and found that it had jumped timing, chain is loose with tensioner all the way out. My cam has some wear and the head and valve cover are damaged at the end of the cam pretty good. Looks like it needs a bit of parts..

https://cimg9.ibsrv.net/gimg/atvconn...f356c6718e.jpg
https://cimg7.ibsrv.net/gimg/atvconn...d8c4b4406c.jpg

Wow, looks like classical oil starvation in the head. Did the quad run out of oil?

This may all be fixable with a new head. There is a good chance that oil starvation destroyed your cam journals before
anything bad happened to other bearings in the lower part of the engine, or the rings. Your 150psi compression test proves
your rings, at least, are OK.

Those were awesome machines, I can well remember when those came out in the market place. A write up from one of the big atv magazines stated" how could anyone ever need any more power than what these machines put out" ? They were king of the hill when compared to everyone else's 230 and 250 machines. I had a Kawasaki Praire 300 for 16 yrs and thought I would never need any more power, it went everywhere I ask it to go without issue.

If you go for a used head, the head and cam cover will have been machined together, so buy the pair. Never known an air cooled engine that didn't seize the little end and/or piston first, when starved of oil, but have had the same failure on a Suzuki 400KQ due to gasket goo blocking the oilway to the head. We got a local engine machinist to bore the cam journal oversize and fit a sleeve on the cam, as Suzuki heads are expensive.

That's a great innovative fix, MM, but what was the cost of line-boring new cam journals? You are correct, a used head is going to be spendy.