Ready to go back to stock EX Cam!!! Help please.

After reading all of this, all I can say is: I'll take my bike to a local shop and have mine installed professionally. Holy shit, what a pain in the ass nightmare! I've got the same bike and the same Hotcams exhaust cam. I'll gladly spend some money to avoid the pain Josh has gone through. :applause:

What Josh is going through in pain and headache :bonk: is IMHO concurrently giving him heaps of knowledge about the bike, so at the end hopefully the good outweighs the bad, and all he lost was some ride time.... Hang in there Josh the lurkers are pulling for you.... :applause:


Did you ever find the spring that you dropped into the engine?

How far down did it go?

My suggestions would be to pull the cylinder since you have the head off and re-ring the piston.

It also would not be that expensive to send the cylinder to Millenium have it replated and honed ($113.00) and replace the piston with a new OEM yamaha piston and ring set.

This way you have a complete new top end.

What a shame it would be to get it all put back together and find you have no compression and a stuck ring after all of this?

Buy a Cometic gasket set or an OEM set if you like but unless you are overboring the cylinder use an OEM piston.

If you wanted to big bore it to a 446 then get the JE piston part # 175001 and have Millenium or US Chrome keep the piston to wall clearance at .030mm or .0012 in.

The bottom line is you have the top end 80% apart, don't sell yourself short and NOT inspect the piston and rings while you are this far in.

Don't be afraid of compressing the rings to get the piston back in the cylinder either, you do that on the bench and then install the piston and cylinder as a unit onto the rod.

Sounds hard but it really is easy, I have done it twice myself..

It is nice to have an extra set of hands at this stage.....someone to support the piston and cylinder while you put the wrist pin clips in place.

Heres some pics of the way I did it.








Just keep everything clean and notice that I put duct tape over the oil line holes, water pipe holes, and also note that you need to order the rubber O-rings that seal the water pipes, new copper crush washers to seal the oil lines and use the same oil you run in the bike to lube the cylinder wall before you install the piston in the bore.

Also use an air gun to blow out all the holes and water jackets in the cylinder and head and clean everything really good with acetone before you oil it and put things together.

Also make sure you scrape the sealing surfaces of the head to cylinder contact as well as the cylinder to case contact spotlessly clean using a razor blade and acetone, and also place a good clean rag inside the cavity where the exposed crank and rod are immediately after you pull the cylinder and BEOFRE you try to get the circlips off the wrist pin when pulling the piston.

If you need more help and or want to talk to someone on the phone PM me and I will gladly give you my phone number and walk you through it when you need help.

Please explain to me what is a stuck ring and what causes it? Would you see evidence of this on the cylinder wall? I don't have a lot of money to dump into this, so upgrades are out. I just want to get it back together and make it run again. Thanks,


Josh, if I were in MO I would give you a hand with this. I have done alot of engine work, just not much on these bikes. I am a California Chiefs fan so I can't be much help to ya. I do have to say that your handling of your situation has been pretty damn impressive and I am pulling for you along with what seems to be alot of other TT'ers. I definately agree with Teamscream that as far in as you are, you should do some intesive measuring at least and see how worn the cyl walls are. if they aren't out of spec, then F'it, throw rings at it and go back together with it. Good luck and please keep us posted as you have been doing all along.


Please explain to me what is a stuck ring and what causes it? Would you see evidence of this on the cylinder wall? I don't have a lot of money to dump into this, so upgrades are out. I just want to get it back together and make it run again. Thanks,


I went into this in detail on

THIS THREAD scroll down until you see my post, another member has a similar situation and I gave all the reasons I have seen personally or come across in my experiences.

P.S. if you are not going to go with getting the cylinder replated and honed, the next level down would be to get a new piston kit (comes with rings, circlips and a wrist pin) or the next step below that would be to just get a set of rings and gaskets AND THE WATER PIPE O-RINGS along with oil line copper crush washers and put it back together, use a little bit of silicone spray or cooking oil on the rubber o-rings and rub them between your thumb and finger to saturate them before putting them in....good practice with rubber.

keep us posted.


I am inclined to believe that the piston and cylinder are in good shape. This engine has very low hours on it for it's age. I bought it new in NOV of 2004, it was a showroom leftover. I would say it may have 50-80 hours on it tops. Regular oil changes/filter cleanings and the standard maintenance stuff. It ran very strong until I tried to put the hotcam in it, and that is when it went to crap. After reading your post on the other thread, I am still not clear on what a stuck ring is and why it would cause a loss of compression. Also, what should I expect to see for compression on this engine with the stock cam? Thanks,


I am still not clear on what a stuck ring is and why it would cause a loss of compression.
I think he is talking about blow by, where the rings don't seal. Did you go through heaps of oil???

No, not a drop. Guys, This engine was in like new condition before I installed the hotcam. It ran great, all I wanted the hotcam for was the autodecomp.


I took the cylinder to a highly recommended old guy to have it honed. New rings and gaskets come in Wednesday. Back together with it next week sometime, wish me luck everyone. I did not end up finding anything wrong, the cylinder was barely broken in, the piston looks and measures like new, the valves don't leak, the gaskets look good but I guess you can never tell. Wish me luck, if nothing else I have been learning a ton about this motor. Thanks for all of your replies, and I will let you all know how it turns out.


Right on jb!

Just take your time and make sure you have 2 types of torque wrenches before you start.

One that does foot pounds down to below 7ft/lbs

And (or) one that does inch pounds (the cam caps).

WASH the cylinder with warm soapy water after you get it back from the hone job then blow it out with air and immediately wipe it with the oil you will use in the engine (use your fingers) make sure you get oil everywhere on the cylinder surface. Also oil the wrist pin holes in the piston.

Put the piston (with the rings properly lined up) into the lightly oiled cylinder bore while it is on the bench. Put the wrist pin into the piston on ONE side I put it on the side I am NOT going to be standing on so I can see the hole in the rod and get it lined up easily (which would be the cam chain side), I also put one of the circlips in the piston (cam chain side) so I know when the wrist pin is all the way in when I connect it to the rod.

Put the base gasket in place on the bottom of the cylinder (use a small amount of silicone seal to keep it in place)

Slide the cylinder and piston down on to the rod and push the wrist pin through the rod until it stops on the circlip you installed.

Then put the other circlip in (this can be a bit tricky but take your time and use tiny needle nose pliers and a small steel pick to get it seated properly).

Once the circlip is in place, spin it around a little bit in its groove to make absolutely certain it is all the way in its groove, it should rotate fairly easily.

Then you have to pull the cam chain up through the hole and secure it with a piece of wire to the frame or whatever.

Then make sure you put the cam chain guide (the exhaust valve side) down through the cam chain opening of the cylinder and get it in place properly.

Then rotate the flywheel while holding the cylinder and piston as a unit so that you can get the cylinder flange down all the way into the cases.

Then lock the cylinder down.

If you don't have a couple of 3/4" drive deep sockets to slide over the head bolts then make sure before you start this process you get a foot of 1/2" PVC pipe and cut a couple of short pieces to place over the bolts with a couple of washers large enough cover the top of the PVC pieces run these down through the holes in the cylinder to lock the cylinder in place so you can rotate the engine and watch the piston go up and down in the bore before you put the head on, this just allows you to make sure the rings are not hanging up and that everything rotates freely BEFORE you put the head on, once you put the head on the head gasket and torque it, the head gasket is finished, theres no taking it back off and using it again so this step helps you make sure you are ready to put the head on, and clean any little debris that might have fallen into the bore while you were working and add one more coat of oil to the cylinder before you put the head on.

I don't use assembly lube on pistons or rings I use the oil that I am going to run in the motor.

You can however use assembly lube on the wrist pin if you want to, its not a bad idea, I use oil there as well.

After you have rotated the motor a couple of times, inspect the bore for any scratches that might indicate a ring digging into the bore, then rotate it to TDC and follow the head assembly procedure in the manual and you should be good to go, make sure you use clean rags to plug any holes as you build upward, it would be a bummer to drop a cam circlip down the timing chain hole after you get that far into the build so cover your tracks as you go.

Like I said before, if you have any problems at all you can call me on the phone and I will walk you through whatever you need help with.

Its not that big of a deal but you don't want to have to take it apart because you forgot one step along the way like getting the cam chain guide in its little lock down position (hint hint).

Good luck with it brother!



keep this post going. I'm lookig at replacing my ex cam and can't decide on HOTCAMs or OEM '03 450 Cam. Waiting to see what caused your pain though. Good luck!

OK Guys,

I have it all back together in stock form with YZ timing. Kicked 3 times and she fired right up. The only problems I noted during the whole tear down were this. One intake valve was at .102, specs say .100 to .150 so I went ahead and re-shimmed this valve. The other thing I found was that when I got the new rings, they were much tighter against the cylinder walls. I don't really know of a good way to explain this, but they had considerably more force outward than the original rings did.

Basically I found that I am capable of tearing down the engine, but I still have no diagnosis for the original problem. And at this point I am just happy to hear that sweet thump thump again. I am going to leave it alone for a while, and will decide later on which way to go with the decomp upgrade. Keep the Hotcam, or go the 03 YZF route. Thanks for all the help guys.


Glad the bike is OK and you are back up and riding! Maybe the new Hot Cams were just not right to spec? Send them back to Hot cams for inspection and then you will know if you want to try to put them back in or not. See you at Chadwick this spring TT ride! :thumbsup:

I bought ex and in cams from hotcams myself.. The ex with decomp, did not push down the valve enough for decomping, so i had to kickstart my bike.. The starter couldnt manage to start the bike..

I sendt them a email, and they actually sendt me a new cam for free! Thats customer service!

Problem is, that i measured both ex cams to be exactly the same, so i did not mount this.. I put back the stock cam, and love my el start button the way it is supposed to work...

Havent contacted hotcams about this again..

you have me all worried now, my bike is doing EXACTLY the same thing, BUT, all i have done is installed a new cam chain and timed to YZ, it ran good the first time, but with a very high and unstable idle, then after that i could hardly start it, kickbacks a lot and backfires, and would only try to start then die, i thought it was a jetting issue so i got a new plug and rejetted, i havnt tried to start it since, but it gets me thinking it could be an issue with the timing chain perhaps??


My kick back problem was my mistake it timing the hotcam. If it is kicking back you have probably moved the cam too far. With the piston at TDC, you should have 12 pins in the chain between the 12 o'clock timing marks for YZ timing and 13 pins for WR timing. Your cam lobes should be facing outward from center, and the exhaust cam will be slightly elevated in reference to the head with yz timing. If you have the means to take and post pictures that would be helpful. Hope this helps.


im working in a wr400f 99 model, ill take off the head cover and take some pics at TDC. i also installed a kibblewhite valve spring kit at the same time. hmm ill post later tomorrow with pics



Sorry, I read your signature and then edited my earlier post while you were reposting. Take a look, and if you want I can give you a call right quick.


no worries thanks for that, im in australia though :thumbsup: but ill definatley post some pics

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