NEED HELP 426 Piston Problem!!

[3wildones]

OK-I'm the mom asking the question here - so forgive if I don't use all the correct terms, dad's at work and I'm doing this for him. Our son has an 01 400ex which he wanted to improve on. My husband has always done the 2-stroke thing so learning the 4 stroke motor has been a learning experience. We have a couple of friends who have done alot of work on these but not to this extent - here's the problem. He wanted to go up to the 416 (wiseco piston kit) and did so. Had it bored out by a professional and had the valves and all checked out at a local atv shop (not a honda shop though). All went back together, but seemed to have a little rough sound - anyway it blew. Valves ended up hitting the piston and broke and came out the exhaust. OK - tore it all apart again, got a 426 kit and mechanic said to have the new piston "shaved off" 120 thousandths. Had it rebored, had the piston shaved, put all back together and found the valves to be hitting again - so stopped everything. He has a stage 3 hot cam and apparently this is too much. So for now they put the stock cam back in - but now is back to square one on the "power" thing. Yesterday, went to a race and had a guy suggest a "JE" piston, he said that this won't hit the valves and would work with the hot cam. NOW --- after buying 2 new piston kits, is this necessary or is their another fix for this problem that we are just overlooking?? This is my son's project and he is trying to keep it as affordable as possible. The new 426 piston is also a Wiseco. Also - are their any other tips for doing this - my husband and the friends helping are very experienced and with motor work - just new to the 4 stroke, and are just needing advice from someone who knows the answer to this situation. Thanks so so much for any advice!!!!

[underpowered]

the vavles should never hit the piston. is sounds as if your timing is off. it the timing is off in the engine the valves will open to early or close to late causing them to contact the piston. i would check the timing. also check to make sure the timing cahin is not stretched. if it is, it could cause enough slack to allow some slight contact. a new piston will not solve anything, it is something other than the piston causing this to happen. i am running a 426 with the old stage 2 hotcam with a wiseco piston with no probems in over 3 years. It is not the piston, but somehting in the valve train.

[F-16Guy]

All HotCam cams are drop-in cams, so it isn't really possible for the valves to be hitting the piston if everything is assembled correctly and the piston is 12:1 compression ratio or less (most common with Wiseco is 10:1 or 11:1). Piston installation is basically the same as a 2-stroke, just make sure that the ring gap is set and things are lubed with fresh engine oil during assembly. Here are some things for your husband and son to look at when putting the top end and cam back together:

1. The engine needs to be at top dead center when installing the cam. Remove both round plugs in the left crank case cover (flywheel cover) by unscrewing them with Allen wrenches. Use a breaker bar or wratchet and a socket on the flywheel bolt to turn the crank counter-clockwise. While slowly turning, look in the small hole and line up the line next to the "T" on the flywheel with the notch on the cover.

2. The HotCams cam doesn't use the stock decompression mechanism, so you'll need to remove the plunger (small steel rod) and spring from the head inboard of the cam gear.

3. Make sure the cam is installed with the lobes facing down with plenty of assembly lube on all bearing and lobe surfaces. There are three marks on the cam gear; when installed properly with the piston at TDC, the cam lobes should face down and two of the cam gear marks should line up closely with the valve cover gasket surface while the third faces up. The timing chain tensioner should not be installed while doing any of this; wait until after the cam is installed.

4. The cam bearing with the rubber seal needs to be installed on the gear side with the seal facing away from the gear. This is very important to the lubrication of the top end because the seal creates an oil pocket at the end of the cam and forces oil into the cam and out the journals.

5. Once the cam and the valve cover are installed, you'll need to install the timing chain tensioner. First, remove the Phillips head screw (it's really just a cap) from the tensioner. Now retract the tensioner by pushing in on the plunger while turning the small flat blade screw clockwise until it stops. It should stay retracted as long as you don't mess with the screw. Carefully install the tensioner and gasket and tighten bolts. Now unscrew the flatblade screw to place tension on the chain. Finally, install the Phillips screw cap.

For bolt and nut torque specs, print this page:
http://www.atvriders.com/articles/torque400ex.html

[3wildones]

Thanks so much for the fast responses!! Talked to husband and he said there he feels there probably is a little stretch in the chain. OK - so I just ordered a new one. Now is there anything else that I should get to go with that. Nothing is broken or worn or anything. And the step by step instruction were great! He felt that he followed those pretty much, but I'm printing them off to have them just to make sure when this thing comes apart again to replace the chain. Also - when setting the timing - exact steps to doing this would be helpful (that may have been part of the last post, but I want to make sure that he has that). He felt that he had it in "time" - but still kinda questioned it. So any very explicit instruction on that would be great!!! He also wanted me to ask what the other marks on the flywheel were for?? I noticed 2 marks, then an "F" and then the "T". He just wondered what the other marks besides the T were for. Thanks for all advice and help on this!! My son (and husband) have been beside themselves on this.

[GPracer2500]

The "F" mark is an ignition timing mark (not to be confused with anything to to with the valve timing). The "F" indicates initial ignition advance. Those other two hash marks that are farther away are the final ignition timing indicators. The ignition timing changes as the RPMs go up.

ETA: Also, if you guys don't have a service manual then that would be at the top of my short list. If for no other reason, it's necessary for the nut/bolt torque specs.

[F-16Guy]

I kind of doubt that the timing chain could stretch enough to cause valve interference, but a new chain couldn't hurt anything. Where did you get your chain? Was it for the 400ex? You can get a timing chain for a 2002 CRF450R (dirt bike) for about $27 from Service Honda. That chain is what most people use because it's the same length as the 400ex chain, but there is one extra plate per link which makes it more resistant to stretching. I have one in my engine, and I used one in a 406 that I built. It's a direct replacement; no modifications necessary (and much cheaper than stock or "heavy duty" repacement chains).

[3wildones]

Ordered a stock 400ex cam chain from Honda of Troy. Screwed up didn't I. Oh well - I know it will be right - but coulda saved some money going with the other. If the timing chain had a little stretch and the timing was incorrectly set - would those have caused the problem together?? I know that he was really having a fit when he was trying to get that set correctly. He thought it was basically right but said it could have been a little off???? Is there ANYTHING else that could have caused the valves to hit. OH - When he put it all back together the second time after the rebore and the shaving - he also put clay on top of the piston and turned the motor over by hand to see if it was hitting. (was told to do this by a mechanic). There were NO marks in the clay at all - but yet when everything was reassembled and started up - they started hitting. ??? Oh - and exactly which manual should we get - I've been looking and find "repair" "owners" etc etc -- several different ones. Which is the one we need??

[F-16Guy]

You want either a Clymer repair manual or a Honda Service manual. The Service manual will have every detail you could possibly imagine, and would probably be overkill for a top-end rebuild. A Clymer manual will cover everything you need plus some, and it's far less expensive. You can order one online or get it at your local cycle shop.

Type into Google: Clymer repair manual, trx400ex

[cals400ex]

yeah get a service manual for sure!!!!!!!!! you need to put a small piece of clay over the valve reliefs. i will post a picture to show you that not much is needed but it needs to be in the proper place too. if the valves were not hitting the clay then something had to be wrong. either you used too thin of a piece of clay or everything wasn't installed. when you turn the motor over you need to make sure you install everything including the valve cover on the 400ex. the valve cover needs to be on in order for the valves to move. so the cam, cam sprocket, valve cover, etc all needs to be on the bike. also, you need to make sure your valve clearances are correct before you turn it over as well.

timing the bike:


turn the crank with a 17mm socket counterclockwise to align up the T. put the cam in with the lobes facing down. the cam sprocket will have 3 dash lines in it. two of those lines are to be parallel with the top of the head. so, you need to look from the side of the motor with you being eye level with the cam sprocket. then look to make sure the dashes align with the head. these dashes are not to be parallel with the ground. since the top of the head isn't parallel with the ground, neither will the dash marks. the third line must face UP, not down. i find it easiest to put the cam sprocket on the chain first. see how it aligns with the head. if it is not right take the sprocket out and turn it so it aligns with the head while NOT rotating the cam chain. then i put the cam sprocket on the cam with the cam lobes facing down. i check the dash marks again to make sure they align with the head before i tighten up the cam sprocket bolts to their 14 ft-lbs. i use locktite on those bolts too. but if you are claying the motor first then i wouldn't use lock tite this time because you will have to take it all back down to take the clay off of the top of the piston before you can start the bike anyways. after the cam sprocket bolts are on then i rotate the crank with that 17mm socket. i make several revolutions. i then come back to the T mark when the cam lobes are facing down. NOTE: the cam lobes will be facing up if you rotate it 360 degrees. you need to make two full rotations for the lobes on the cam to be facing down again. after you are on the T with the lobes facing down then double check to make sure the timing is right. are the two dash marks parallel with the head? is the other dash mark facing up? after this you can put the head cover back on. tighten it down and check the valve clearance.

[cals400ex]

also, with the hotcam you do not use the spring and plunger in the head. you will see a spring and plunger in the head under the camshaft. the hotcams do NOT use these so you take them out before assembly.

here are pics of clay on top of a piston before clay checking a motor. you do not want a lot of clay or it can get stuck in the valves etc. i use fairly small pieces in the middle of the valve reliefs. also, i put the clay on about 1/4 inch tall. this is a 450r motor with a thermal coated piston but you get the idea. the concept is the same.


also, you will need a valve job at a minimum after wrecking your valves. your head may even be trashed. let someone that knows what they are doing determine that.

[cals400ex]

claying motor:

[smitht316]

just an idea.... but is the piston in backwards..... i know the arrow has to point towards a certain way. dont know off the top of my head but im sure someone out there knows it

[F-16Guy]

Originally posted by smitht316
just an idea.... but is the piston in backwards..... i know the arrow has to point towards a certain way. dont know off the top of my head but im sure someone out there knows it
That's a good question. The arrow on a Wiseco piston should face forward, toward the front of the quad (or case, if the engine is out). Good thought.

[3wildones]

I'll ask the husband when he gets home - never heard him say anything about that, so could be??? New camchain is on the way as well as Clymer manual. This info is all great! We appreciate anything you can tell us!

Marcie

[-copyguy-]

Originally posted by 3wildones
I'll ask the husband when he gets home - never heard him say anything about that, so could be??? New camchain is on the way as well as Clymer manual. This info is all great! We appreciate anything you can tell us!

Marcie

Sent you a PM. might help you get started before the Clymer gets there...

[cals400ex]

instead of messing with arrows on some pistons and others not having arrows.......take the head. put the piston below the head and line up the larger valves with the larger valve reliefs. if nothing else, this is just a good second check.

[prepracing]

also what kind of head gasket are you running, some builders try to squeeze some extra compression out by only running one layer ( out of 3 ) of the stock honda gasket set. And with some setups thats doesn't leave enough clearance...... :devil: