|
Author
|
Topic: Excessive wear? (valves)
|
ukracer
Gearhead Posts: 164
From: South Wales UK
Registered: Apr 2003
|
posted 01-19-2004 09:42 AM
   
I have pulled the 351W out of my circuit race Mustang for a quick rebuild and to fit bigger SS valves. As the engine was built about 15 months ago and has only done a few thousand miles and 8 races, I was not expecting too much damage. However, most valvestems seem to have worn badly (guides were bronzewalled and new stock valves) with a noticeable ridge (mikes to 1/2 thou). On top of this, the tips of some valves were mushroomed enough to take a file to get them out, as well as the keeper grooves which had to be filed to get the valve out without damaging the guide. Also the tips of some valves were badly brinnelled and chipped (has roller tip Magnum rockers). Cam is a CC XE268 with .512/.520 lift (IIRC) and correct springs at correct height. Has spring cups. This engine has never seen 6000 rpm and has only been to 5500 a few times. I am a little disappointed at the short life of these parts. Any thoughts?
IP: Logged |
Moneymaker
Administrator Posts: 26811
From: Lyons, IL, USA
Registered: May 99
|
posted 01-19-2004 10:14 AM
Geometry is off. The rocker arm roller tip is not riding centered throughout the valve travel.
You need to change the length of your pushrods.
PS, normally mush roomed valve stem tips are a sign of valve float. FYI------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
IP: Logged |
ukracer
Gearhead Posts: 164
From: South Wales UK
Registered: Apr 2003
|
posted 01-19-2004 10:30 AM
I have always been very picky about geometry. The wear patterns are almost perfectly centred on the tips and I have watched the roller cycle across the tip and it looks very good. If you are referring to the valvestem wear, the odd thing is that it appears to be more 'sideways' than 'forward', so it is at 90 degrees for the normal thrust face. It has rail-type rockers (race rules) and uses the valve tip to laterally stabilise much of the valvetrain.
I know that floating valves hammers them to death but I have never heard it and like I say, it has the right CC springs at the right installed height and it has not been over-revved (remember my first ever post- won't rev past 5000?) I am not arguing with you Alex, I appreciate your experience but I have honestly checked the geometry and am just trying to give more info to try to track down this problem. Thanks.
Cheers, Martin.
IP: Logged |
Moneymaker
Administrator Posts: 26811
From: Lyons, IL, USA
Registered: May 99
|
posted 01-19-2004 10:54 AM
Martin, no arguing at all, just hypothisis.
Look closely at the valve springs then.
Look between the coils for signs of chaffing.
That would be a certain indicator of valve float.------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
IP: Logged |
bluestreek
Gearhead Posts: 1724
From: Athens,GA
Registered: Jul 2001
|
posted 01-19-2004 11:22 AM
I agree with Alex. Sounds like some valve float going on. When you rebuild the heads, make sure the springs give 125# seat pressure. Make sure the springs coils are not binding. The stainless valves will be less prone to chipping and mushrooming. You might also want to use titanium retainers (if rules allow) to loose some valvetrain weight.------------------
1966 Mustang Coupe: Custom glass hood and BIG scoop sits atop a 289 stroked to 331 c.i., Steel crank, rods and girdle, TFS alum. heads, Stealth 8020 intake, Xtreme 268 Solid Roller, Holley 750 HP, long tubes, 4speed, 9" 3.50 posi.
11.86 @ 116 mph (7.62 @ 93 mph)daily driver!
DanH
IP: Logged |
ukracer
Gearhead Posts: 164
From: South Wales UK
Registered: Apr 2003
|
posted 01-21-2004 04:27 AM
Sorry to come back on this but I am confused.
The 'right' springs for this cam are 942's. According to CC's website, these springs spec at 115lb @ 1.7" and are for up to .500" lift. This cam is over .500" lift.
I have closely inspected the springs and there is no sign of contact. Valve float would certainly explain some of the problems I have had (not revving) but I don't see how it's happening. My 460 has CJ valves and 3/8" pushrods (heavy), single springs and RPM cam with .580" lift and regularly sees over 6000rpm. Has been like this for 9 years, so why does my little 351 have a problem?
IIRC Comp list a 972 as 'premium' for the XE268 but has more installed height. What problems can I expect if I have more seat pressure. (over 125lbs)?
Cheers, Martin.
IP: Logged |
Moneymaker
Administrator Posts: 26811
From: Lyons, IL, USA
Registered: May 99
|
posted 01-21-2004 09:31 AM
Two other possibilities.
1)Look at the bottom of the valve spring retainer and see if it has been making contact with the top of the guide.
2)This is one that we have experianced ourselves. Valve bounce caused by inadequate spring pressure. Although rules dictate a stock valve lift of .445 in our stockers, the cam profile we use in Tony's record holding Capri is rather "radical" to put it mildly. We found out on the dyno that we would suffer valve bounce about 5500 RPM. This is in effect the valve hanging open after being bounced off of the seat. We thought that 125 lbs of seat pressure was plenty, but we were wrong. We changed springs right on the dyno (to 972's ironically)and that cured the issue up to 6200. We set them up at 160 lbs. We later improved the seat pressure even more and have no valve bounce at all.------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
IP: Logged |
ukracer
Gearhead Posts: 164
From: South Wales UK
Registered: Apr 2003
|
posted 01-21-2004 09:39 AM
Alex, thanks for chiming in again. I am strongly suspecting inadequate springs and feel that Comp have recommended the wrong ones for the job. Seems like I might have to step up to 972's and the changes to accomodate them. :-(
Still, if it cures the problems, it will be worth it. From what I have been reading on the net, weak springs may explain why it has been insensitive to tuning. Thanks again.
Cheers, Martin.
PS, would you care to stab a guess at the sort of springs/pressures I need?[This message has been edited by ukracer (edited 01-21-2004).]
IP: Logged | |
Mustangsandmore Forums
