Seized intake cam on 250F :(

[jimt_yz400]

I really hate to admit this but I screwed up my 250F. I know that some of you will look at me as being a idiot but nevertheless we all make mistakes, unfortunately this one will be costly.

This is what happend:
I installed a new piston and rings into my 250F. It really didn't need it after measuring the ring cap of the old gap but I did it anyways since I planned on racing the D36 Enduro series in NorCal.
This went well and I rode the bike for few miles on Sat. But there was a pblm. The bike would idle at 2000 or more rpm and would not always fall. I thought that it was jetting of and air leak but it didn't
act like it had an air leak of lean on the bottom. The bike ran great all over but it would idle really high.

I found out later that day the I had the exhaust and intake cams one tooth advanced. Ok, so last night I adjusted them and set them the way that manual states.
The next it would not start. I checked tht plug and it was fine. I then took it to the track and a friend of mine took the valve cover off and we checked the cam timing and I adjusted the fule screw a little and it then fired right up, idled perfect and had good throttle response. My son took it out to the track and it died on him before he could get there. I gave him my bike to ride and jumped on the pblm bike. I started if and it it idled fine but then died and made a strange "clank" like a chain being yanked after it died. I then pumped it through a few times and it seemed to be ok, no weird sounds etc. though it did feel a little stiff going thru the stroke when I was attempting to kick start it. It then started right up and I rode a few laps (two) then it started to have some low end response pblm like low fuel/low float bowl level.

I took it back and shut it off. It then was very difficult to kick over though not like a piston seize.

Ok, I tore it apart and here is what I found:
Intake cam wwas difficult to rotate, the exhaust was ok. I removed the intake cap and cam and the journal nearest the clutch side was scoured as well as the cam and the cap. There was also some scoring on the other journal on the intake but not as bad. The exhaust was scored very little but it's not perfect.

So, what the hell happened? Everything else in the motor (I haven't split the cases yet) looked ok ie: the piston and cyl and cyl head looked great. Did i screw up in placing the cams back in, not
torquing it down correclty or did I not oil the cams well enough or is there a pblm with the oil pump?
Can the cyl be repaired or is it now a through away item? I notice that Yamaha sells the head and caps (for the cam) as an assy.

I'm very *P*&%ed that this happened since I usually have alot more luck in all of the motor work that I do so it's very disheartening to think that I actually caused this!!

Any ideas???
:( :( :(

 

[jimt_yz400]

I meant to say :
Can the Cyl head cam journal be repaired or do I have to buy a whole new Cyl head assy ($548.00!!!!!!)?

The BIG issue here is what really happened!!! If it is the oil pump then there
probably is a heck of a lot more damage. The thing is that there was lots of oil
in the cam area, it wasn't dry. The oil pump source is at the same area where the journal is seized/scored. This is the source correct?

This REALLY makes me want to buy a 2-stroke again!!!

 

[SFO]

Call Mike @ EDCO.
Engine Dynamics

He can clip cam caps and rebore/hone the journal area.
I have seen his repairs and they are flawless.
Tell him Big Bill formerly of Kibblewhite sent ya.

 

[jimt_yz400]

Bill,
Does this sound like an oil starvation pblm? The more I think about it that is the only thing that makes sense, or maybe oil failure (Motul 3000 10W40, non synthetic). I might even take the engine to someone to split the cases since I'm *very* depressed and kind of feaked that I actually DID something.
Really I'm not a novice at this so to have something like this happen is kinda
weird.
Where is EDCO (Engine Dynamics )? Is it in SF? Do you have the number?

 

[SFO]

If it ran fine before, I would be hard pressed to say it was a lubrication problem.
It could have seized for a lot of reasons.
Call megacycle and ask them for edco's #, or Kibblewhite.
I am just building my rolodex again and don't have the #.
I believe you will be able to get it right.
Mike is a great head guy, has a serdi, welds, has a machine shop, superflow, and yada-yada-yada...
He will figure it out and stand behind his work.
If you want to cruise by the shop and check me out, or if you want assistance with putting it back together again, I am still game.
Bill

 

[jimt_yz400]

Found their number, they are in Petaluma:

ENGINE DYNAMICS COMPANY, LLC. THE PERFORMANCE PEOPLE. 1010 Lakeville Street Petaluma
CA 94952 edco@enginedynamics.com. Phone (707)763-7519 / Fax (707)763-3759. ...
http://www.enginedynamics.com/
I'll be in Berkeley this morning so maybe I'll drive up there to have him take a look at it. I feel that I need to have some check the rest of the motor out and I do have some freinds that can split the cases but I feel that I need someone that knows what they are doing, especially if this was the sympton and not the cause. We need to find the cause!! OTherwise it'll happen again.
THX for the info!! I may take you up on the assembly, though I'll probably need to spit the cases ans go thru everything or have someone do it for me.

Know a good bulider that can inspect the engine and diagnose the pblm or are you one?

 

[bashn]

Did you pay careful attention both the dissassembly and reassembly instructions? The manual very aggressively states the cam journal covers must be loosened and tightened in STEPS. I loosen the the bolts in three steps, using the specified pattern in the manual. Failure to adhere to this procedure could result in cap warpage, which in turn will sieze the cams. Did you try rotating the cams by hand after torqing the caps? They should turn smoothly. Another trick I learned from another manual is to generously oil the cam during installation and pour plenty of oil onto the top of the head after installation.:)

Mark

 

[will pattison]

after 3 yz thumpers, i can say that you are not alone, and i am not an amateur mechanic. yamaha has made it very difficult - at least on the bigger motors - to get to the cam cap bolts on the intake side. unless you have a wobble socket or some other trick up your sleeve, the frame's backbone is right where you need to be with your torque wrench. since the caps are very sensitive to how tight they are, this can mean big trouble.

i have seen slight galling on the cam caps even when the torque wrench said i did it right. my only conclusion is that because the bolts and the corresponding torque values are so small, that the margin for error is equally tiny. in those cases where there was a bit of galling, i have always been able to clean them up and get things working fine. it takes a bit of fine emery cloth, some wd-40, time, patience, and a good eye, but it can be done. it certainly costs less and is less hassle than buying a new head or having the damaged one repaired. not knowing how bad yours is, i can't really suggest what you should do, but i thought you might want to know my experience.

what would be really nice is if yamaha would put some sort of replaceable insert in there....

 

[Farmer John]

I have had Mike @ EDCO do work for me before.
The man walks on water in my book!
94 XR650L- fixed head after both ex seats came out & fragmented.
90 DR650 - repaired cam journals
SRX 600 - took a trashed head & made it perfect.
Aprox 8 or 9 SR/TT/XT 500 road race motors - I asked that they be able to run with 4 valve XR motors on a road race course. They were not the longest lasting motors, but that is not what I asked for.

 

[DualSportr]

We have seen MANY of these failures from overtightening of the cam cover bolts on the 400 and 426 (we don't have any sponsored racers running the 250 this year). Lots were done by race mechanics, so if it makes you feel better, you're not alone.

Although this issue is covered in the manual, it really doesn't stress it enough.

Anyway, basically what we've learned over the years is that everything that will rotate in the engine once it's together should be rotated and lubricated prior to final assembly. Same is true of cranks, gear assemblies and bearings in the lower end, and also cam rotation. It's easy to pinch camshafts in many different engine models (including XR80's and 100's), so it really is something that should be checked.

Anyway - we have saved one head like this - it was for a sponsored racer of ours - the head had dozens of hours of porting work done to it, so we felt it was worth salvaging. It took our shop another 8 hours to fix, and the cover had to be torqued by our R&D head guy and nobody else. It's a delicate operation, and easier to mess up than do right.

 

[jimt_yz400]

Bashn,
How do you tunr the cams if the chain is attached ? Do you mean install the intake w.o the chain on then attempt to turn it ? I always have a pblm with getting the chain on so I have to losen both cams to get the chain on. Maybe I can bolt the intake down and play around with the exhaust cam to get ti all aligned.

The failure is able to be fixed, it'll be about $350.00 with a high performance
valve grind. The REAL pblm is how the hell dis this happen!! The cap can only go on one way and that is down. So as you bolt if on it should go into place.
I 'll check all oil lines and the pump..........what else?
I'm still beside myself that I might have initiated this failure!!!

 

[jimt_yz400]

DualSportr.... you're making me nervous!! I was told that I should ONLY torque to 5ft lbs not the specified 7.5 by the guy doing my head work. He will also make the cap/cam clearance a little more than what stock specified.
Stock it VERY close, .8 thousands to 2.1 thousands. After the failure I could
not find a plastiguage small enough to mearure the clearance (of course not,it was barely moveable!!)

 

[Rich Rohrich]

Originally posted by jimt_yz400

Stock it VERY close, .8 thousands to 2.1 thousands. After the failure I could
not find a plastiguage small enough to mearure the clearance (of course not,it was barely moveable!!)

2450x01 Green plastigage will cover that clearance range. I've found that not aligining the cam gears correctly side to side can cause also the cams to seize at initial startup. If you look down the cam chain line from the top you can get a visual clue as to the relative location. If the cam bearing are properly lubed a VERY light tap with a screwdriver handle is all it takes to align them. If they aren't lubed or the caps are over torqued they won't budge and there is a high probability of trouble.

 

[jimt_yz400]

Rich,
Yes I used red so that's why it didn't work. I'll be EXTRA careful next time and maybe to this when I'm not tired from a day of riding and hopefully before 11PM so that I get it right. This isn't the 1st time that I've had the cams off of an engine. I've checked all of the 400's and the 426 that I had and I've never had a pblm........its just a little strange that's all.
Thx for everyones advice on this. I hope it WAS a bad install of the cams/caps and not an oil pump pblm.......the piston looks great so I don't think that it is a pump pblm but........:o

 

[jimt_yz400]

Thx for all of the feedback on my pblm.

I put the bike back to gether this weekend and took it on a long ride (about 30 miles). It seems that I had warped the cap when I was torquing it down.
I obviously did not have it installed correctly when I was tightening the cap bolts. Engine Dynamcs did a great job with the head. They gave me a 3 angle
valve gind with some cleaning of the ports (a mild porting job) which beleive it or not did affect how the bike runs. It pulls harder in in the mid than it did before and seems to want to rev a little easier. I m really happy with how it turned out and thx to SFO for recommending Mike at Engine Dynamics. I might have him do my other bike since I am truly impressed with how well it
runs after the valve grind and the porting.

Also, I'd like to thank the folks that gave me the tips on moving the cams after
you have all of the caps torqued. If you have the plug removed you should be able to move the cams with your hand and there should be no binding.

Cheers!!

 

[SFO]

Jimbo...

Mike has saved my ass countless times...
#1 Pro-stock gs1150 head seized the cam like your yz...he welded and bored/honed the cam journals
#2 ex Spencer head I got enthusiastic replacing the guides and cracked the head in many places. He welded the guide bosses back into one piece and blended the porting job so the customer(or me) couldn't tell that his priceless head(to him) was almost ruined.
Thats just off of the top of my head(sic)!
His prices are reasonable as well, its like he doesn't know what those so-cal rapists are getting for this kind of work.:D
I also know a guy that is his equivalent for big twins, but that might be a different subject.
I am glad that he worked out for you.
What do you think about going to mikes sky ranch for x-mas / new years?:)

 

[jimt_yz400]

Mikes Sky Ranch? Sure!! Sign me up. But for the whole entire week(s) of Xmas and New Years or was it Xmas or New Years? I'm sure that the wife would be kinda pissed if I was gone that long. Let me know what you're talking about, more info pls!!
jamest@netapp.com