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Author Topic:   Valvetrain Troubles
ryan
Dirt Forum Champ
Total posts: 776
posted May 08, 2005 06:45 AM  
This might we longwinded but here we go. Last night I get going in hotlaps and feel something break, pull off and pull a valve cover and see a broken stud(screw in) on #7 exhaust, changed that went out for heat race and it missed bad so I pulled off right away I got back pulled the valvecover again thinking maybe we lashed on the wrong stroke and found the rocker next to it to be very loose so..we pulled that rocker and noticed the stud was marred up on the bottom and the pushrod cup on the rocker was cracked and the pushrod was bent about 4 different ways with a small piece still left down there. This was just on #7 and its the same setup as lastyear, but with new springs(same brand, style, part number) The week before we had replaced that rocker because it was blue on the bottom. Last year we had problems breaking them because of hitting the guides, which have since been machined down, so we were used to the discolored rocker. What are some solutions to this. I'm thinking bent valve or maybe a guide that is seizing up. When we assembled the heads I didn't notice any valve going in any different than the others I dont know how the valve could be bent without hitting the piston. Could the stud have broken on the exhaust and then caused the problems on the intake side because the pressure? Don't really seem like a oiling or geometry issue because its just on that one.

[This message has been edited by ryan (edited May 08, 2005).]

istock2
Dirt Newbie

Total posts: 4
posted May 08, 2005 09:25 AM  
what lifters are you running

ryan
Dirt Forum Champ
Total posts: 776
posted May 08, 2005 10:27 AM  
Solid, ran same cam and lifters as last year.

mod2_x
Dirt Full Roller

Total posts: 38
posted May 08, 2005 11:05 AM  
Ryan, I am not much of an engine guy and this is the first time I have heard someone say that they lashed on the wrong stroke. We recently checked valves and I to am having a missing problem which you have replied to. I cant help but think that this may also be contributing to my problem. What would be the effects of setting valve lash on the wrong stroke?

ryan
Dirt Forum Champ
Total posts: 776
posted May 08, 2005 11:47 AM  
I didn't lash on the wrong stroke we just checked that guess I didn't need to put that in there
We just pulled the head and the valves are straight and the guides feel fine. I did however find that it looked like the intake gasket was possibly leaking water into that hole and the piston was very clean almost new looking and its been raced one full night, practice and about 4 laps last night. I don't know I'm lost. Could it be the stud was bent during the winter by us or the machine shop, on the rocker we took off it the ball wore a grove into the rocker. I would just take it as a stud breaking and either the pressure of no exhaust or the poly landing just right to bind up the intake side if it weren't for the blued rocker the week before.

Mod We lash ours like in the toolbox, one group turn it over and do the other group. On that method anyways if you lashed at the wrong time I would think that it would be very loose because you would set it when it was supposed to be already down or part way down.

[This message has been edited by ryan (edited May 08, 2005).]

ryan
Dirt Forum Champ
Total posts: 776
posted May 08, 2005 08:23 PM  



 
Here's some pictures. Rockers new this year this is the only one like it was pulled off last week.

Raz_900
Dirt Forum Champ
Total posts: 635
posted May 08, 2005 08:52 PM  
IMHO, you're coil binding the springs or sumthing of the sort. There always has to be a valve or 2 that are the shortest installed height. There's pretty much nothing else that will break valve train parts like that.... well, excessive valve float will. But I'm betting on coil bind.

rico 08
Dirt Forum Champ
Total posts: 1139
posted May 09, 2005 05:50 AM  
looks like the rocker was turning sideways and causing that groove,probably coil bind.When the exhaust broke that made the intake break.

IowaFuzzy1
Dirt Maniac

Total posts: 136
posted May 09, 2005 07:11 AM  
How much lift on your cam?Too much lift with stock type rockers causes the rocker to slide back and forth rather than just rock .this causes excessive heat and also puts an excessive side load on studs and can cause binding which will bend push rods and cause the splitting of the rocker such as you have.This is accumulative stress,it dosen't just happen.If its leagle in your class your best bet is to switch to roller rockers.Good Luck

ryan
Dirt Forum Champ
Total posts: 776
posted May 09, 2005 04:39 PM  
I'm going on the third year with this setup we checked clearances on one cylinder but not all of them this is the first broken stud unless I got a bad spring on that valve. I will double check before re-installing tho.. The cam I run is a 530/550 lift. I run 1.46 crane springs 998931. The are advertised up to .600 lift in one catalog and to .650 in another.
Roller Rockers are a no go a few have tried and failed.
Can anybody tell me why the stud broke and the pushrod was straight? Why on the intake side did the pushrod bend and leave the stud? They pushrods are the hardened type for use with guideplates but they aren't the moly ones. I think the bent pushrod on the intake side came after the exhuast stud let go. Thanks

UPDATE: I checked how much clearance I had on the head that was still on the motor and at full lift on the exhaust side there is .095 more on the intake

[This message has been edited by ryan (edited May 09, 2005).]

ryan
Dirt Forum Champ
Total posts: 776
posted May 10, 2005 04:11 PM  
Any more theories than coil bind I thought minimum was .050. I find it hard to beleive no one else has had this problem.

rico 08
Dirt Forum Champ
Total posts: 1139
posted May 10, 2005 04:26 PM  
If the exhaust breaks then the pressure that would normally go out the exhaust will just stay in the cylinder..then when the intake tries to open it can't so the pushrod bends,just like using air to hold the valves and change the springs,same principal.that's alot of lift for a stock rocker.

ryan
Dirt Forum Champ
Total posts: 776
posted May 10, 2005 08:14 PM  
I agree with you on why the intake went out but I want to find a reason on why the exhaust went out, just so I can prevent it from happening again, if it wasn't for the blued rocker the week before I wouldn't worry about it. I guess I'll put it back together and keep an eye on clearances and if it happens again I'll say screw it and park it. I dropped from 10th to 24th or so last week.

El Santo
Dirt Full Roller

Total posts: 36
posted May 10, 2005 10:24 PM  
Look at the pushrod slot on the cylinder heads where the pushrods come through. If there is any amount of side wear that will cause your rocker arms to be cocked to one side, especially with that much lift, and will put the stud and rocker in a bind and it will break. We had a good set of heads that the slots got wore out and I had to drill out the pushrod slots and go to long slot self-aligning rockers, and that fixed the problem. If you're running oil restrictors with stock rockers, TAKE THEM OUT! They are doing you no good.

ryan
Dirt Forum Champ
Total posts: 776
posted May 11, 2005 08:44 PM  
I run guideplates in Bowtie heads and they are fine. I think I found the problem my installed hieght was wrong and caused excessive spring pressure.

iowatoolman
Dirt Freak

Total posts: 369
posted May 11, 2005 09:55 PM  
sorry its to late to get in on this but i had a machine shop do the same thing to my heads but instead of too much it was not enough i ended bending all the intake valves and a couple of exhaust valves

oh yea btw use the scorpion roller rockers i have had very good luck with them just make sure to get all of the assembly grease out by soaking them in thinner or solvent then dry them with air pressure then soak in oil before putting them on your motor

live and learn

drive hard or drive home

[This message has been edited by iowatoolman (edited May 11, 2005).]

ryan
Dirt Forum Champ
Total posts: 776
posted May 11, 2005 10:51 PM  
Roller Rockers are illegal.

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