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View Full Version : Piston to valve clearance??


Hot Wheels
04-09-2009, 12:29 AM
what kind of clearance should i have between the piston and valve??
sbc

lun40119
04-09-2009, 12:46 AM
I am running .060, and .105 on 4.125 bore.....that is safe. I know there are guys running alot closer, but I tell you what when you look in the exhaust port, and see what .060 looks like........................:eek:

Awesome Bill
04-09-2009, 10:34 AM
You can run the intake as close as .030 and the exhaust as close as .060. The intake valve is chasing the piston and the piston is chasing the exhaust valve. So if your timing chain has a little stretch under proper loading, the piston to valve always gets closer on the exhuast. This is why exhuast piston to valve should always be maintained @ .060, you can loose .050 easy and especially is the engine runs backwards!

Hot Wheels
04-09-2009, 11:57 PM
Thank you Very Much!!!

Trmnatr
04-10-2009, 03:28 PM
Thank you Very Much!!!

What is your clearance now ?

Awesome Bill
04-11-2009, 10:56 AM
Not a problem @ all

JAKEJR266
04-21-2009, 10:32 PM
Depends on how much you want to push the envelope. CompCams recommends a minimum of .100/.125, In/Ex.

Jake

Awesome Bill
04-22-2009, 09:32 AM
that is for horse shoe players who flock shoot!

lun40119
04-22-2009, 09:34 AM
That is fricken funny :D :D :D

Hot Wheels
04-24-2009, 02:17 AM
hahaha that is funny Awsome Bill

Awesome Bill
04-29-2009, 11:11 AM
Even the bible says laughter is as good as medicine!

JAKEJR266
05-22-2009, 08:14 PM
OP asked about PV clearance. I didn't just pull those numbers out of the air or made them up. Everything I've read from the pros, including Engine Masters, Chevy High Performance, GM High-Tech Performance, on and on, all say .100/.125.

In an interview with, I believe, was a CompCams Tech guru, he went so far as to say don't even start your engine if you have less than .100"/.125". The entire interview is in one of the mags I have around here somewhere and if you're interested in reading it, I can probably track it down and post the mag issue.

Of course, if you choose to disregard that advice and run tighter clearances, be my guest; it's your engine. Tighter clearances are only SAFE up until the point that the piston and valve have an unhappy meeting.

Like the guy on another Forum who recently was at the top of second gear (6000 rpms), went to hit third and mistakenly went back to FIRST - BANG!
It's your call.

Jake

West Point ROCKS!

JAKEJR266
05-23-2009, 12:58 AM
I found the specific quote in a CompCams catalog: "Do not try to operate the engine with less than .100" clearance on the intake and .125" on the exhaust. Costly engine damage will occur."

Once the engine floats the valves, the piston will catch up and hit a valve (usually an exhaust) while it's hanging open and before the valve has time to close.

So it becomes an issue of not "if", but a matter of "when".

As I wrote before, it's your call.

Jake

West Point ROCKS!

jerry clayton
05-23-2009, 02:43 AM
It will always be an exhaust that gets hit---

Intakes should have a minimun of .020 at about 10 degrees past top center and exhaust at before top center---of course when you get this close the valve notch needs to be in the exact correct place---the closet comtact point can be at the edge of the notch as the relative motion between the valves and piston are somewhat sideways

want-a-be
05-23-2009, 08:19 AM
I found the specific quote in a CompCams catalog: "Do not try to operate the engine with less than .100" clearance on the intake and .125" on the exhaust. Costly engine damage will occur."

Once the engine floats the valves, the piston will catch up and hit a valve (usually an exhaust) while it's hanging open and before the valve has time to close.

So it becomes an issue of not "if", but a matter of "when".

As I wrote before, it's your call.

Jake

West Point ROCKS!

Guess I've been doing this wrong for the past 25+ years then. I use a minimum of .095" @ about 10 btdc for the exhaust and about .045" @ about 10 atdc for the intakes.

If the springs are set up correctly for the application then valve float shouldn't be a problem.

Don

lun40119
05-23-2009, 11:14 AM
Guess I should take mine apart then. .060 and .105. John Gardner who built the short block, assured me that I am fine. Guy worked on Greg Anderson's PS team, before consulting with some local shops around the Madison area. Seems to me he even built a SBC for Matt Kenseths personal vehicle. There are alot of things Jake that you read, that may be a little safe. The experiance that these guys here have, some of them should be writing the books.

It isn't that I dont agree with you, you should look in one of my exhaust ports during overlap when the piston is near TDC. :eek: And it has been to 8000.

want-a-be
05-23-2009, 01:09 PM
Guess I should take mine apart then. .060 and .105. John Gardner who built the short block, assured me that I am fine. Guy worked on Greg Anderson's PS team, before consulting with some local shops around the Madison area. Seems to me he even built a SBC for Matt Kenseths personal vehicle.

LOL Greg Anderson!!?!?!?!! who is he again??? Working for someone like him then what would Mr Gardner know? lol...kidding of course. Sounds like he did a great job on from what I've seen.

Have a good weekend bud.

Don

lun40119
05-23-2009, 01:22 PM
Nice to see you back again Don. What you been up to. How is Wayne County Ill treating you this time of year. John is a really great guy, he is the guy that did the no-hole balancing, and also did all the dyno work on mine, as well as Jims 502. Either way good to have you back.

lun40119
05-23-2009, 03:46 PM
It will always be an exhaust that gets hit---

Intakes should have a minimun of .020 at about 10 degrees past top center and exhaust at before top center---of course when you get this close the valve notch needs to be in the exact correct place---the closet comtact point can be at the edge of the notch as the relative motion between the valves and piston are somewhat sideways

Jerry, what do you use as a rule of thumb for the exhausts at 10 btdc??? Do you mean you use .020 on both???????

jerry clayton
05-23-2009, 04:19 PM
If you are running the cam at where you only have around .020 the exhaust will be .075-.080 or more---I have only gotten close because of advancing or retarding the cam to move the power around for down low or top end.

However--as rod ratios affect the piston acceleration/deceleration at top center, the rates of closure do vary and an exhaust vale that maybe had lost a spring or starting to sieze in the guide could be slowed enough to allow piston contact.

Any failure in the cam drive system will make instant junk no matter what your clearances are

The biggest recurring thing that causes a problem with valve piston clearance is uncompatibility of valve angles and/or the curvature of the valve notch is not concentric to the valve centerline---

several times when examining an engine I have found rub marks about half way down the valve notch, indicating that the relative motion between the piston valve is not a simple straight line motion.

And then these days, with valve centerline spacing moved this way so much, that way so much, then head angles changed, how do you possibly hope to get parts out of a box bought on line or E bay that will work together???

lun40119
05-23-2009, 04:38 PM
I agree with you there, when I first brought all my crap to the machine shop, John was very worried bout the Mahle pistons working with my cam. Not so much the ptv depth as the radius of the valve contacting the notch like you say. He actually had one of my cylinder heads shipped to him from the cylinder head guy, so he could mock it up so he knew for sure. I told him I had planned on mocking it up, but he wanted to be sure in his mind. I guess I don't blame him. Then friggen UPS lost one of my cylinder heads, and that is a whole other heart attack that happened while building this turd :D.........

JAKEJR266
05-23-2009, 04:55 PM
As I wrote before, each person can run whatever clearance he or she choses; it's their choice. Yet when a poster asks what clearance he should run, if I choose to respond, I feel obligated to give him what could be considered as the industry standard recommendation.

I recall back in the day (close to 40 years ago) when I was young and limber, I once built a 468 BB for one of the teams I use to build engines for that I'd tightened the quench so much that the intake valve was actually kissing the piston. Upon tear down for freshening, I could see definite indications of how much I'd pushed it. Engine was never hurt from that, but it's because I was more lucky than smart.

The last engine I built, a 434 Mini-Rammed SBC using 15 degree Brodix heads, BowTie block and Jesel shaft system, when I mocked it up, the P to V was too tight. So I tore it down, removed, then had all the pistons fly cut and everything re-balanced. Even though it called for more work and extra cost, that's how strongly I felt about those clearances.

Don't get me wrong, I'm not trying to change anyone's mind. I'm only the messanger here, trying to pass along information I've learned over the years. Being 64 years old now, I've finally learned not to take unnecessary chances or, if you do, sometimes you'll bite the bear and sometimes the bear'll bite you.

Jake

West Point ROCKS!

lun40119
05-23-2009, 05:07 PM
You don't have to defend your answers Jake.

jerry clayton
05-23-2009, 05:21 PM
Jake---I don't have any problem with what you told the op.
I was adding comments about the total picture of v/p clearance issues and what I have run things to. Forty years ago--those bbc were decked way down to get the pistons dome up higher to where the flat part of the piston needed to be cut also---of course then the valve pockets needed to be cut especially for the 2.300 intakes--still have the alum vise plates for my mill to cut the angles that the valves were out---then came angle milling the heads, the Dart heads that were already laid over and on and on


By the way---thanks for the help with the postings on the LT SHP !!!!!

Jerry

PS
Tell us about West Point-----

Awesome Bill
05-27-2009, 10:28 AM
You have to remember when people like the tech guru @ comp cams? who the hell is he and what has he built? these people tell you this to keep is so safe you will never be really fast. On Comp Eliminator engines, we have run the intake valve as close as .025 on the intake and .040 on the exhaust @ 10,000 rpm. Now Jerry is absolutely right about piston speed, rod angles piston to valve and head angles all playing a part. A simple valve with a point on it @ 10-5 before TDC will put you near perfect position to put a little mark on intake and exhaust. Now take a dial caliper and lock it in .050" larger than your valve and trace out the pattern holding one end on the dot and walk the other around the notch. If it is anywhere near the line, you have to remove it and also use a radiused cutter.

Now for you boyz who just want to stick a big cam in and sound great with out checking anything, use the .100" method. but you have to remember as soon as you start the engine, you loose .050 on the exhaust and gain .050+ on the intake. So your .100" for either theory is bull____!. You will always need a little more on the exhaust because of stretch and cam twist if you have it.

If your engine floats the valves, you have junk anyway so go ahead and bust her up so you can fix it to make some power. Valve float? what the hell is that with todays parts. If you want to hold the hydraulic lifter motor over 6000 rpm with a heavy 2.3 or larger intake valve then you might as well take a ball peen hammer and smack your head with it few times just to do it to see what happens.

Every combination has its proper installed parts and skilled labor to make sure it matches your combination. People on tech lines are some times idiots! Of course no one @ Dart is like this, but a lot of times they are just people who have been put into a position of general knowledge and they are following simple basic very safe guidelines.

If an engine is put together by a professional who does this, it will not have any problems with piston to valve even as close as .010 on the intake valve!. The engine better not run backwards for sure, but at that spec, with a steel rod, it will never touch the piston and if it does, it will leave the name of the valve manufacture into the piston and not hurt anything. I have done it and seen it many times. Exhaust the same way but with more ptv starting. Most of us has seen the racoon eyes on the tops of pistons on nice race engines that operate well above 7000 rpm. If I am wrong on this you let me know.

Mu rule of thumb for a novius is .060-.100 on intake and exhaust and you better not be playing with clay unless that is all you got! use a dial indicator and a pair of checking springs with the head gasket and the parts your going to run and the geometry pattern better be .010-.020 wide pattern on the valve tip!

JAKEJR266
05-29-2009, 06:00 PM
West Point? That's my son; he's what they call a "Firsty", beginning his fourth and final year there. He graduates next May and will be conmmissioned as a 2nd Lieutenant, majoring in Law. Right now he's at Ft. Hood, near Killeen, TX doing a summer assignment there. He's going AirBorne too; wants to jump in as the tip of the spear.

He has a month "off" before returning to the Point in mid July. During that off time we'll pull the engine on his 96 LT1 Vette and install the new Dart Pro1s, RRs and a custom ground CompCams HR I spec'd and bought. I chose Comp's CRC lobes. We're shooting for max torque, so I kept the duration on the short side but the valve lift high.

I'll be using the clay method to check piston to valve, since I've used that method since Hector was a Pup, about 30 years or more. Even Comp says it's the easiest and perhaps most accurate method to use. I prefer to follow the recommendations of the engineers who test and come up with what to do and what not to.

By the way, when I applied for acceptance to the Point, I was told I was too old; guess they're right since I'm 64 years old, LOL! I already did Air Force, back when Viet Nam was going Hot and Heavy.

Here's a little more info:

I've got a Harvard grad too, Electrical Engineering, class of 2005. The US Government gobbled her up and right now she's working in the Embassy in Algeria.

Another one skipped high school altogether; went straight to college from the 8th grade. She graduated with a B/A in Photo Journalism in 2008 at age 18 and is now working in New Zealand.

My last cutie-pie is a Junior at Howard. She's the "Environmentalist" of the family.

They're all doing well; I like to think it's genetic, LOL

Sorry for getting off topic so much, just couldn't resist the opening.

Jake

West Point ROCKS!

lun40119
05-29-2009, 06:12 PM
Jake, I am not making heads or tails of that post.........Did I provoke that???? Eitherway, sounds like you have some kids to be proud of.

JAKEJR266
05-30-2009, 05:12 PM
Jake, I am not making heads or tails of that post.........Did I provoke that???? Eitherway, sounds like you have some kids to be proud of.


LOL, no not you.

Jerry Clayton asked me to tell him about West Point, so my response sort of took on a mind of it's own. Sorry 'bout that.

Jake

West Point ROCKS!

Awesome Bill
02-14-2010, 11:04 AM
what kind of clearance should i have between the piston and valve??
sbc

You can run as tight as .025" on the intake and .040" on the exhaust with steel rods, aluminum you better add .020" and rpm factor will cause the exhaust to get tighter. That is how close we have run them.

I suggest, keeping .060" on the intake and .080" on the exhaust. If the engine runs backward, you could have problems and tighter than these #'s

JAKEJR266
02-14-2010, 06:41 PM
Wow, and all the time I'd thought this one had quietly slid off into the sunset. LOL

Even though over the years I've run P/V so tight the valves actually kissed the piston, leaving nice little witness marks of what had happened, I definitely DON'T recommend it.

When it comes to things like this, I revert to the industry, generally recommended clearances. Clearances found in catalogs or websites of CompCams, Crane, Lunati, etc.

CompCams newest catalog, 106-07, recommends a minimum of .100" on the intake and .125" on the exhaust and also recommends the clay method, even showing diagrams on how it should be done.

Should someone choose to deviate from those recommendations, all I can say is "Whatever"

Jake

West Point ROCKS! Nation's Top College Per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

Awesome Bill
02-15-2010, 10:28 AM
Wow, and all the time I'd thought this one had quietly slid off into the sunset. LOL

Even though over the years I've run P/V so tight the valves actually kissed the piston, leaving nice little witness marks of what had happened, I definitely DON'T recommend it.

THAT IS WHY I SAID I HAVE RUN THEM THAT TIGHT BUT SUGGEST THE .060 AND .080. OBVIOUSLY YOUR HAVING PROBLEMS UNDERSTANDING WHERE YOU GAIN PV AND WHERE YOU LOOSE PV WHEN IT ALL GETS UP AND RUNNING.

When it comes to things like this, I revert to the industry, generally recommended clearances. Clearances found in catalogs or websites of CompCams, Crane, Lunati, etc.

YOU HOLLOW ABOUT INDUSTRY STANDARDS AND KEEPING IT SAFE BUT SAFE RARELY MAKES REALLY GOOD POWER!

CompCams newest catalog, 106-07, recommends a minimum of .100" on the intake and .125" on the exhaust and also recommends the clay method, even showing diagrams on how it should be done.

HAVE YOU EVER LOOKED @ WHAT .100" IS? THAT IS LIKE DRIVING A BIKE DOWN A 4 LANE HIGHWAY WHEN IT COMES TO HAVING ENOUGH!

Should someone choose to deviate from those recommendations, all I can say is "Whatever"

THAT IS WHY PROFESSIONALS CAN GET AWAY WITH THE AS TIGHT AS AND YOU CAN ONLY HOPE TO!

Jake

West Point ROCKS! Nation's Top College Per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

Just as many perverts and do nothings come out of the really good colleges as the not so good ones, and that is a fact! Just because someone goes to WEST POINT means only 1 thing, you paid toooooo much!

JAKEJR266
02-15-2010, 12:47 PM
Here's a photo of me in a roadster I built the +.100" BB engine for and use to drive in quarter mile runs. This was taken more than 20 years ago at Great Lakes Dragway in WI as I was about to warm the engine before time trials.

It ran 8-teens in the quarter mile at 175+ MPH and has the engine I referenced having valves that kissed the pistons. Most often, though, it ran mid-8s because of an intermittent trans brake issue I could never resolve to the point I felt confident of it working properly. In staging. I'd occasionally get pushed through the staging lights causing a RED LIGHT. So in competition, I had to resort to brake torquing.

Although the engine in the photo ran a tunnel ram, the other BB, normally aspirtated engines I built ran single Dominators, were all under 500 CID and still ran 8s, but with 25 or so less MPH of course. On those single carbed engines I maintained SAFE piston to valve clearances.

Back then I kept written records on all the engines I built including all the clearance specs. Yet, over time and in moving from one state to another, the records got away from me. It's been a long time to remember all the clearances, but IIRC only one engine I built had less than .100"/.125" and (from memory) it ran .080"/.100".

I warned the car owner but he didn't want to shoulder the cost of the machine work. I also told him, his driver and their friends that I wouldn't be responsible for a valve train failure like bent valves, broken rocker arms, etc.

The owner promised to let me have the clearances opened on the first freshening of the engine, but he never did, claiming that since he was running a Power Glide it would be okay. No problem ever occurred though, but on each pass I had my fingers crossed, LOL


I do specifically recall, though, that on another engine (not sure which), during mock-up, I found the piston to valve too tight and tore the engine back down to have the valve pockets deepened and the balance re-checked.

There's no end to the different specs engine builders use - seems to be as much an ART as it is a SCIENCE. Yet when clearance issues arise on this Forum or on the several others I visit, I recommend those that are generally recommended by industry leaders, not necessarily those that I've "tried".

I'd HATE to recommend something that could end up damaging someone else's engine. Besides, the difference in running UNSAFE/QUESTIONABLE clearances Vs those that are SAFE doesn't translate into much improved performance anyway. Certainly not enough to justify taking the chance.

Occasionally, on other Forums, I've read where a member missed a shift and bent a bunch of valves. Four Forums come to mind, CF, ThirdGen.org, CamaroZ28 and LS1LT1 if anyone would like to track them down. Summer of 09 seems to be the time frame I read the last one, but I didn't make note of which Forum.

As with many things, choosing to push the envelope is an option, but most often, not the recommended ones. Ask the engine builder if he'll cover the repair costs should his non-recommended clearances prove to be diasterous. I already know what the response will be.

However, as I've written many times before, "To each his own".

We should be done beatin' on this by now; I know I am.

http://i140.photobucket.com/albums/r21/JCAMERON266/KIDS/SCAN0011-1.jpg

Jake

JAKEJR266
02-15-2010, 01:18 PM
Oh, as an off-topic, side note, your West Point comment was unwarranted and offensive as I'm sure others will also agree. No need to be jealous of my son's accomplishment and success. Comments like those let your TRUE personality shine through for all to see.

And to just clear up another indication of your obvious lack of knowledge, West Point doesn't cost the Cadet or his family any money; NONE. It's paid for out of income taxes, Department of Defense appropriations budget.

That budget is funded from Income Tax, and, if you DO pay income tax, thank you for your financial contribution to my son's education and for his service to the defense of the United States of America.

Members are taking notice of what you post, just in case you aren't paying attention. Becomes an issue of credibility.

With that, I plan to completely ignore any of you future posts and I'll see if I can find a way to block you entirely. Beyond that, any future posts of a similar, negative, personal nature will cause me to report them to a Forum Moderator asking that punitive action be against you. YOU ARE FOREWARNED!

Jake

jerry clayton
02-15-2010, 01:34 PM
Jake

94 days and counting---Congrats to your entire family. I'd hate to think that West Point didn't exist and where our country would be without it and Annapolis-----Hmmmmmm, thats in Maryland, isn't it???maybe that explains Bill's remark??? Army/Navy????

I worry more about stopping from 175 at the Grove than the valve/piston clearance!!!

Jerry

Dart Vader
02-15-2010, 02:07 PM
Just as many perverts and do nothings come out of the really good colleges as the not so good ones, and that is a fact! Just because someone goes to WEST POINT means only 1 thing, you paid toooooo much!
Is it really necessary to go for personal attacks on other forum members?
This comment was out of line... whatever your personal feelings may be, there is no need to insert them in this thread. They aren't relevant and they're very combative.

The board isn't here for this sort of thing.

JAKEJR266
02-15-2010, 02:41 PM
Jake

94 days and counting---Congrats to your entire family. I'd hate to think that West Point didn't exist and where our country would be without it and Annapolis-----Hmmmmmm, thats in Maryland, isn't it???maybe that explains Bill's remark??? Army/Navy????

I worry more about stopping from 175 at the Grove than the valve/piston clearance!!!

Jerry

Yes, in MD. I even took Ryan there for a tour when he was considering going Navy. We had a Navy Commander visit our home a few times trying to convince Ryan to go Navy. An Air Force colonel tried his luck, too. He visited use a couple of times. None of that worked though, primarily because he'd done Army ROTC in highschool.

Thanks for your well-received comments. Yes, I'm proud of him beyond words. I've got a Harvard grad too, with the D.O.D., also. She's attacking the wars from the other direction, Intelligence.


You're right. P/V was the fartherest thing from my mind on the top end, especially when I couldn't see anything directly in front of me. Now factor in night-time runs and things REALLY get exciting!

Each time I pulled the chute handle I said a prayer, LOL.

One time the chute wrapped around the wheelie-bars without deploying and I barely had enough room to stop. Imagine my feelings when I had thoughts of meeting up with the passing traffic. CRASH, BANG, but no 'Thank You M'am'. LOL

Team use to hate for me to pop it because they had to re-pack it - Hel*, I'd done my job, right?

Of course all this was when I was young, limber and didn't know any better, LOL.

Jake

jerry clayton
02-15-2010, 02:52 PM
Had that wheelie bar/chute deal happen only once---also stuck throttle only once--lucky wasn't at the Grove but they both did happen on the same run--luckily it was at Byron and I finally got stopped way down by the nuke towers---chrome trim blew off the windshield---figured must have got up in the 190s before got it shut down

JAKEJR266
02-15-2010, 03:02 PM
Had that wheelie bar/chute deal happen only once---also stuck throttle only once--lucky wasn't at the Grove but they both did happen on the same run--luckily it was at Byron and I finally got stopped way down by the nuke towers---chrome trim blew off the windshield---figured must have got up in the 190s before got it shut down

LOL, sounds like FUN! Those were the days.

Isn't Byron the track that had the starting line pad re-done and afterwards no one - with any kind of power - could launch? Seems like that was the track we went to for the very first shake down pass after Leon bought the Roadster.

IIRC I was warned by the starter not to try to drive through it if the car got squirrelly. I still did a sharp 90 though. LOL

Man, does this bring back memories.

Jake

JAKEJR266
02-15-2010, 03:07 PM
BTW, we solved the chute/wheelie-bar problem by installing a Cup Car window net between the two wheelie bars. Then the chute would bounch off the net, back into the airflow and blossom.

How'd you guys solve your problem?

Jake

jerry clayton
02-15-2010, 03:12 PM
I let someone else drive after that

JAKEJR266
02-15-2010, 03:29 PM
I let someone else drive after that

LOL, now why didn't I think of that!?

Jake