valve job
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Senior User
Joined: Dec 2001
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valve job
guys
as i posted before, im rebuilding my own heads because of a burnt exhaust valve. i have a question though. these heads look like they were recently rebulit because they still have the spiral knurling marks down inside of the guides. if they were indeed rebult not too long ago, why in the heck would all the valve guide seals be sooooo brittle; brittle almost to the point of breaking apart when squeezed with yr fingers? moreover, why is there a ton of black junk under the heads of the intake valves YET the exhaust valves are clean? lastly, they are completely disassembled on my workbench. i was thinking of porting them buti dont know where to start OR IF IT WOULD BE A GOOD IDEA on a stock engine! any thoughts??
thanks
as i posted before, im rebuilding my own heads because of a burnt exhaust valve. i have a question though. these heads look like they were recently rebulit because they still have the spiral knurling marks down inside of the guides. if they were indeed rebult not too long ago, why in the heck would all the valve guide seals be sooooo brittle; brittle almost to the point of breaking apart when squeezed with yr fingers? moreover, why is there a ton of black junk under the heads of the intake valves YET the exhaust valves are clean? lastly, they are completely disassembled on my workbench. i was thinking of porting them buti dont know where to start OR IF IT WOULD BE A GOOD IDEA on a stock engine! any thoughts??
thanks
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Senior User
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valve job
DF--its a 72 360. if you are standing in front of the truck looking at the engine, its the front-most cylinder on the drivers side(the one closest to the rad! as for grinding the seats----nah! i was gonna clean everything in kero real good then re-lap them with polishing compound! new seals would do it; am i missing something? i really cant afford a professional rebuild at the moment!
Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
valve job
I have done several valve jobs with a suction stick and rubbing compound before but never with a new or different valve. I'm pretty sure that when you install a new valve you should cut and grind them.
Cargo Master
Joined: Aug 2000
Posts: 2,931
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From: SW Michigan
valve job
Nut, what are you talking about-polishing compound?! Sorry guys, the stuff doesn't work. Doesn't do any harm, but the only thing it MIGHT be able to do is make you feel better. Your valves and seats are hard, and that paste is not. Don't waste your time. If you want your valves to seal properly, you have to cut the seats and grind the valves. A complete valve job would set you back about 225$, plus extra if you needed new valves, if you brought it to the shop where I work. I would imagine a local shop could do it for you in couple of days. Surely there is a machine shop within driving distance of you ? Check around, some auto repair shops have valve and seat machines of their own. DF
Senior User
Joined: Nov 2001
Posts: 294
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From: Calgary Canada
valve job
Sounds like the guides might be worn if you have a buildup of carbon on the intake valves. The intakes will suck oil down the valve stem and it will then burn onto the valve. It doesn't happen on the exhaust valves because there is no sucking there, only blowing. If you can feel play with the valve in the guide then it is worn and should be redone. On the other hand if the guides are OK then you probably just need new seals at the tops of the valve stems.
BTW, valve lapping compound is harder than the valves or seats and can be used to lap the two pieces together, but only for very minor touch-ups. If you have a burnt valve, you probably need to have that seat ground. You really should consider having the heads rebuilt at a head shop. It isn't that expensive when you consider the time and work of removing and reinstalling the heads.
BTW, valve lapping compound is harder than the valves or seats and can be used to lap the two pieces together, but only for very minor touch-ups. If you have a burnt valve, you probably need to have that seat ground. You really should consider having the heads rebuilt at a head shop. It isn't that expensive when you consider the time and work of removing and reinstalling the heads.
Senior User
Joined: Jan 2002
Posts: 255
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From: "tween the cotton and tob
valve job
That spiral stuff on the inside of your guides is indeed knurling. Its used when the guide is worn but not worn enough to be replaced. The spiral knurling increases the ID of the guide to match the valve stem and not allow oil to flow past. Its really a temp repair at best. New guides are in order. As for the brittleness.. that may be due to the hardening of the guide whaen it was knurled. When metal is worked cold it becomes what is know as "work hardned". Kinda like bending a piece a metal back and forth. Sooner or later it breaks. Same deal there.
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Senior User
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From: "tween the cotton and tob
valve job
One other note here.. Knurled guides are not al bad.. Knurle a NEW set of oversized guides and it will actually hold the oil and lube the stem of the valve better. This best be done by someone who knows what they are doin. I'm sure some of the older dudes around here will remember the knurled guides and other lil tricks like that.
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Thread Starter
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Senior User
Joined: Dec 2001
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valve job
thanks for all the insight guys. if i really had the cash, id def spring for a total prof. rebuild! HOWEVER, being on a college budget lol, i have to do the most for the least here
if i opt for the good ole new valve/ old un-cut seat/ lap-job, what is the WORST scenario im looking at if it doesnt work AFTER i get it together? i wish i knew how to post pics here because i would put a pic of the burnt valve and a pic of the bare head with a good shot of the seats.....btw..DF, where ya from? im from New Jersey
if i opt for the good ole new valve/ old un-cut seat/ lap-job, what is the WORST scenario im looking at if it doesnt work AFTER i get it together? i wish i knew how to post pics here because i would put a pic of the burnt valve and a pic of the bare head with a good shot of the seats.....btw..DF, where ya from? im from New Jersey
Post Fiend
Joined: Apr 2002
Posts: 7,157
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From: Central Kali
valve job
The seals do become hard after awhile. They can be replaced with the head on the block. I have done this several times. Takes a tool to compress the valve spring. Some use air in the cylinder to keep the valve from falling in. I put the piston at TDC; never had any problems. Have read that hand lapping is not a good substitute for machine ground valves and seats. I think the seal is better with the machine grind.
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valve job
i know i should get it professionally redone but i guess im being cheap? lol one other thing....if i put a new cam in this motor, should i put in new valve springs ect??? i just want to have some fun with this thing. what cam would you recommend? im after gobs of low end torque and a strong mid-range with less of an emphasis on high RPM runs. suggestions? more comments? THANKS GUYS!
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
valve job
Changing your cam does not require new valve springs unless your current springs are worn out or you are changing to an extremely high lift cam. From your description of what you want, I'd say the stock springs are fine for the cam you'll probably end up with. You will, however, need to drop in a new set of lifters, and you should always change your timing set while you're changing the cam. Figure $200 for all the parts needed to do the complete job (cam, lifters, timing set, lube, etc.).
You should check out the FE engine forum for specific recommendations on cams and performance upgrades. There have been lots of threads debating various cam choices, and nobody ever seems to mind debating them again.
You should check out the FE engine forum for specific recommendations on cams and performance upgrades. There have been lots of threads debating various cam choices, and nobody ever seems to mind debating them again.
Elder User
Joined: Mar 2002
Posts: 609
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From: Watauga TEXAS
valve job
I have replaced and lapped in only the burnt valves in my trucks before. Every time I purchase a $500-$700 truck with a serious lope, I find at least 1 burnt valve. I found two in each head one time. I just bought new valves from the local parts store, lapped them in real good, and change the seals. After this "temporary" repair, they've lasted for years!!!
Take a look at your timing chain- a stretched or worn out chain will cause burnt valves!!!!
Joe
Take a look at your timing chain- a stretched or worn out chain will cause burnt valves!!!!
Joe
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