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Valve Clearance Problems!

 
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jeffejoy
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Joined: 23 Jan 2004
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PostPosted: Sat Jan 31, 2004 5:44 pm    Post subject: Valve Clearance Problems! Reply with quote

Confused I just bent all my pushrod on a fresh rebuild because I did not allow enough clearance between my exhaust valve and the pistons. How much will I have to fly cut my pistons to make everything work. Here are my spec's:

Dart Iron Eagle 230 Head with 49cc chamber 1.60 exhaust valve, 2.05 Intake. Pistons .020 down from deck of block. Pistons have .240 dome. 4.030 bore, 3.48 stroke. Head gasket thickness .045 Gross lift on exhaust valve .607 valve time on exh. open at 71 BBDC close at 31 ATDC. Pushrod length 7.950 Rocker arm ratio 1.50 to 1 With the valves closed and the piston at TDC I current have .280 total clearance.

Your Help will be greatly appreciated!
Jeff Ellis
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Hanz
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Location: Casselberry, FL
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2003 Dodge Ram

PostPosted: Sat Jan 31, 2004 5:51 pm    Post subject: Reply with quote

The onle way to know is mock it up with valvetrain, and playdough on the piston, and turn it over. Dissassemble and mic the playdough. You want about .100 clearance, a little less is OK if you have good springs.

I just sold a set of these heads, customer intsalled on a motor with flattops and zero deck, he checked his clearance and had .075, a little small but he's going to run it...first race was today, but probably got rained out...oh well speed week starts Thursday...! Hanz

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jeffejoy
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PostPosted: Sat Jan 31, 2004 5:58 pm    Post subject: Valve Clearance Problem Reply with quote

I have mocked up the engine. There is 0 clearance between the exhaust valve and the piston now. I have about .045 clearance between the intake and the piston. How do I know what how much to cut from the piston dome? Is there dome to cut or will I need to get piston with less dome. Last year I ran the same cam and pistons with 64cc heads with no clearance problems. In an effort get better flow and more compression I upgraded heads. I am afraid I will have to buy new pistons now as well. Don't know if I can afford that this year.

Thanks Jeff
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Hanz
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2003 Dodge Ram

PostPosted: Sat Jan 31, 2004 6:10 pm    Post subject: Reply with quote

My cust had about .010 diff between in/ex. So if you have .045 intake, I would think ex would be right about zero. Maybe open up the ex valve adjustment by say .030, to get a playdough reading, and then add (subtract) the .030 from the reading.

Then you have to either mic the dome/pockets to see if there is material to cut deeper, or look in the piston book sometimes they tell you the dome thickness, or solid/hollow.

Just curious, what piston do you have?

My customer wants to up his CR more, so I was going to call JE and see if they have a 49cc dedicated shelf piston yet. Hanz

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jeffejoy
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PostPosted: Sat Jan 31, 2004 6:21 pm    Post subject: Reply with quote

I had the rocker clearance on the exhasut valve at .020. I actually have less then zero clearance because I not only bent I broke some of my pushrods.

My pistons are speed pro Part#L2252A

Thanks Jeff
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bill jones
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PostPosted: Sat Jan 31, 2004 7:03 pm    Post subject: Reply with quote

-I wouldn't worry about cutting those pistons .100" on the exhaust or intake.
-They are plenty thick to do that.
-Problem is you need to disassemble the engine and remove the pistons and have someone flycut them.
-It would be a good idea to remove the front 4 valves on one head and then make up centerpunch out of an old valve that you can accurately locate the valve centerlines.
-The pistons now are generic meaning you can use any piston in any cylinder but once you have the valve pockets machined that usually makes a small exhaust pocket and a large intake pocket so then you end up with 4 left and 4 right pistons.
-If you haven't removed the heads yet I would also look real close for the dome to be banging the head on the sparkplug side of the dome.
------------------------------
-Since you have bent all the pushrods I would bet money that the valves are also bent.
-The cam specs you list at 71+31+180 is 280 duration but are the timing numbers at .050" lobe lift?
-Assuming they are an example is a Comp Cams #cs316-316-r6 is a 280 duration with .622" lift (measured at the valve-race ready) and the valves are open right at .227"INTand .237"EXH at TDC when checked race ready.
-So you need to know how far open the valves are at TDC not just what the clearance was with the piston at TDC.
-BUT the intake valves hit about 8 to 10 degrees after TDC and the exhaust usually hits about 12 to 8 degrees before TDC so that is where the action needs to checked for sure.
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jeffejoy
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PostPosted: Wed Feb 04, 2004 6:47 pm    Post subject: Cutting pistons Reply with quote

I have talked with a friend of mine that has been racing for sometime now and he told me to try advancing my cam timing by 2 degrees. Yes the specs for the cam were at .050

I agree with you that I may have bent valves. I plan to check them after I have fixed my clearance problem.

I mached up the engine this weekend with no pushrods to measure the clearance between the head and the piston. I have .280 clearance and the dome is not touching the spark plug or head surface.

I will let everyone know if the cam timing change fixing my problem. I am not looking forward to cutting the valve reliefs. My friend is doing this now and stated that he has invested about 3 hours per piston in nothing but labor and then will have to mach up every cylnder again at the end for clearance.

When I advance the cam timing I will lose 5 hp at 7500 rmp but will gain 5 ft lbs torque at 5500 rpm. If my clearance is okay I will end up at 610 horse at 7500 and 500 ft lbs torque at 5500 rpm. My convertor stalls at 5000 with the trans brake on. I am hoping all this equates to a 6.50 at 110mph in the eight. Last year with old double hump chevy heads and only 500 peak horsepower my best pass was 7.11 at 96mph.
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bill jones
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PostPosted: Wed Feb 04, 2004 11:30 pm    Post subject: Reply with quote

-Whatever you do you HAVE TO CHECK on either side of TDC race ready by pulling the valves down with a valve spring tester tool (like a Moroso) or something like that until you can feel them touch the pistons and have a dial indicator on the retainer at the same time so that you can see EXACTLY what you have.
-And then check every cylinder and know what all 16 are doing.
-----------------------------
-When you advance the cam the intake clearance will be less by about .008" to .010" for each degree and you will gain that same amount on the the exhaust.
-You need a least .040" on the intake and about .070" on the exhaust at the closest point of contact and most people want about double that to be safe.
-These numbers of .040" and .070" ARE NOT recommended by anybody but if you have good valve springs and you check each valve and you stay under the valve float limit it is enough.
------------------------------
-Those pistons are one of the earliest designs that TRW ever made for a 350 way back in the late 60's and they don't have deep enough reliefs for big cams and/or high ratio rockers.
-I feel that you are sh-tting your self if you don't get serious and get in there and find out exactly what's happening.
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techinspector1
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PostPosted: Thu Feb 05, 2004 12:54 am    Post subject: Reply with quote

I've cut valve reliefs before using Isky's cutters. It's not that big of a deal. I outlined it for 79_z28406sbc in a previous post. Go about 3/4 way down this page where I start off with the sentence "THE PLOT THICKENS"
http://smokemup.com/bb/viewtopic.php?t=723&start=0

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bill jones
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PostPosted: Thu Feb 05, 2004 1:22 am    Post subject: Reply with quote

-I have Isky cutters and I occasionally use them to fix the edges of valve pockets and to do flattops but when you get to cutting a dome where more than 50% of the Isky cutter is trying to cut or when the center of the Isky tool is upon the aluminum, the going gets very tedious and you need a lot more patience that I have to cut even another .040".
-The mistake here is that the combination of parts have gotten the boy in trouble and to fix it he needs to find out what he's really up against and deal with it the best way he can.
-I cut pistons using a mill and a piston vise and a flycutter and it's really a pretty easy process if you have the center punch marks or valve contact reference, but if the notches need to be done with the Isky tools that's real labor intensive if you have to cut very much depth.
-Been there and done that and that's why I have the real equipment.
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jeffejoy
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PostPosted: Thu Feb 05, 2004 5:03 pm    Post subject: Reply with quote

Thanks to everyone for your information. I plan to advance my cam tonight and check my clearance again. Bill, Thanks for the idea of using the valve spring compressor and dial indicator. I think I can find enough friends to loan me these tools. I just wish I had thought of that earlier.

Yes I understand that my pistons are probably not the best, but I am on a limited budget. My plans were to strengthen the top end of my engine this year. I am sure by next year I will be forced to rebuild the bottom end. I don't think I want to trust the pistons and rods into a third season.

I am in Northern Missouri and we have almost a foot of snow on the ground right now, so I have plenty of time to finish the job. I will keep everyone up to date on my progress.

Come the first race, the first weekend in May I will scan a copy of my time slip. If it is respectable, don't want to embarrass myself. Sometimes there are a lot bugs to work out on opening weekend.

Thanks to Everyone, Jeff
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Hanz
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2003 Dodge Ram

PostPosted: Thu Feb 05, 2004 5:50 pm    Post subject: Re: Valve Clearance Problem Reply with quote

jeffejoy wrote:
Last year I ran the same cam and pistons with 64cc heads with no clearance problems.


The smaller chamber necessitates the valves to be .100 closer to the deck than on (Dart) 64cc heads, which coupled with possible shallow valve reliefs lead to the interferance.

Wiseco has a profile for domed pistons to fit these heads, and I imagine JE does also, but you'll be looking at a 750 dollar bill.

Hanz

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rking
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PostPosted: Thu Feb 12, 2004 12:41 am    Post subject: Reply with quote

Cool
Call Summit and you can custom order Ross pistons for less than 600 dollars if I remember right
they will teell you what they need to know and then take that info too the enngine buils=der to get the right numbers
later and
GB
rk
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jeffejoy
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PostPosted: Sat Feb 14, 2004 2:41 pm    Post subject: Valve Clearance Problem Solved Reply with quote

I have finally solved my problem. I ordered from JEGS some camshaft gear bushings only $24.98 after shipping. The offset bushings allowed me to change the cam timing in increments of 1, 3, 5 & 7 degrees before or after TDC. With my crank gear set at 2 degrees retarded or TDC my exhaust valve hit the piston, with it set at 2 degree advance the exhaust valve cleared by .200 of an inch but the intake valve hit.

So I set the crank gear back to TDC and put a the 5 degree advance bushing in the cam gear. It was a simple installation. All I had to do was drill the bolt holes and the line-up stud out to the diameter of the bushings, 13/32" then insert the offset bushing in the line-up stud hole. After putting in the bushing I used a chisel and made a indentation on both sides of the bushing to keep it from coming back out. The only other thing I did was replace my .018" thick steel gasket with a .045" thick gasket.

After clay checking the pistons I now have .085" on the exhaust valve and .060 on the intake. I know that I am running it close on my exhaust valve, but I am running an automatic so I shouldn't have any problem with missing a gear and over reeving the engine. I have my RPM Limiter set at 8600 and my shift light at 8000. I have been told others have survived with this close of a tolerance. Besides the ultimate goal is to get it as tight as possible to make compression, right?

Thanks to everyone for your help. I have a busy week ahead and I am waiting on a new valve stud girdle to come in so it may be a couple weeks before I can get if fired up again. Besides my driveway is still covered with snow. The last time I tried to fire the car up in the garage I almost burned the house down. I not taking that chance. My wife would never forgive me. Besides I don't have enough home owners insurance to cover the cost of replacing the car.

Thanks again!
Jeff
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