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380 ci sbc bending exhaust valve

General engine tech -- Drag Racing to Circle Track

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gsbrown83
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Re: 380 ci sbc bending exhaust valve

Post by gsbrown83 » Mon Jun 03, 2019 11:10 am

Could it be an intake problem causing a lean condition

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Re: 380 ci sbc bending exhaust valve

Post by Roundybout » Mon Jun 03, 2019 11:13 am

It’s odd it bent #1 so soon after a cool down to get it to the trailer after inspecting. If it was always just #7 I’d suspect the cam or maybe a cooling issue on that cylinder but this happens with different heads, correct? Clearance or seals would be my first guess.

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Re: 380 ci sbc bending exhaust valve

Post by gsbrown83 » Mon Jun 03, 2019 11:17 am

Yes brand new dart heads. Same always number #7. It's far fetched but what are possibilities of lifter bore doing something funny when warm?

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Re: 380 ci sbc bending exhaust valve

Post by Newold1 » Mon Jun 03, 2019 7:28 pm

Does not matter at this point whose heads or whether they are new or not. Even new heads can have valve guide clearance and lubrication issues. When valves hang up in guides while heated from runs they will usually delay closing or opening event timing and the valve will do the "dance" off the top of the piston-whola bent valves! :wink:
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Re: 380 ci sbc bending exhaust valve

Post by makin chips » Mon Jun 03, 2019 7:40 pm

gsbrown83 wrote:
Mon Jun 03, 2019 11:17 am
Yes brand new dart heads. Same always number #7. It's far fetched but what are possibilities of lifter bore doing something funny when warm?
What was on it before those Darts? Same thing?

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Re: 380 ci sbc bending exhaust valve

Post by Keith Morganstein » Mon Jun 03, 2019 8:14 pm

cjperformance wrote:
Mon Jun 03, 2019 6:17 am
Would be great to see a pic of the stem when removed and uncleaned, then after being cleaned with only solvent to remove oil trace.
Pic of seals, pic of un bent stems , clearance on un bent stems etc.
I have had a couple of similar problems come in. One in an iron head was being caused by a lapped over guide k liner, the other in an ally head was caused by a cracked guide insert- cracked in the exhaust port end.
I'd want to see photos too.

I had an issue last year on a SBC marine engine. Bent an Exhaust valve in short hours. The valve stem was galled. Most exhaust Guide and stems showed signs, but only one stuck enough to bend. I installed new guide liners and engine pro nitro black valves. It was fine after that.
Automotive Machining, cylinder head rebuilding, engine building. Can't seem to quit #-o

gsbrown83
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Re: 380 ci sbc bending exhaust valve

Post by gsbrown83 » Mon Jun 03, 2019 9:57 pm

Pictures are hard for me to get as i drop it off to him and he calls with updates. He is old school so probably not big on pictures. Let me ask you guys this what is acceptable seal clearance and or type of seals and valve to guide clearance

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Re: 380 ci sbc bending exhaust valve

Post by swampbuggy » Mon Jun 03, 2019 10:20 pm

gsbrown83...i do not know exactly how much stem to guide clearance you need, but i have known people to run the clearance on the tight side trying to gain a LITTLE power and it has bitten them in the butt. Make sure you are running stem seals that will let SOME oil pass by them. Mark H.

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Re: 380 ci sbc bending exhaust valve

Post by gsbrown83 » Mon Jun 03, 2019 10:41 pm

For the tires we use I've told him I can give up alot of power to help cure this problem. I'm going to drop it back off tomorrow night. Hopefully he can find something bcz it's getting very frustrating

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Re: 380 ci sbc bending exhaust valve

Post by levisnteeshirt » Mon Jun 03, 2019 11:49 pm

Smokey said .003 stem clearance ,, most won't agree

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Re: 380 ci sbc bending exhaust valve

Post by gsbrown83 » Tue Jun 04, 2019 7:11 am

Update we removed engine last night and it has bent exhaust valves on 1 3 7. All intakes are fine. All even cylinders are fine. Am I still looking into lubrication problem and if so is it because the engine oil is all being naturally thrown to right side due to forces on track

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Re: 380 ci sbc bending exhaust valve

Post by Newold1 » Tue Jun 04, 2019 7:49 am

If the engine pan, oiling and windage control is not set up for a circle track race engine and that left side 1,3,5,7 are not oiling properly then that will very quickly overheat valves, springs guides, etc. and valves hanging up can happen for sure. Usually though if oiling from improper oil control is an issue pressures will drop dramatically and other issues will show up like bearing wear and failures. I have seen a few circle track cars with a tattle tail oil pressure light big enough in a conspicuous place to let the driver see he has an oiling problem whatever the cause. Hard to watch a pressure gauge or digital read out when your racing circle track.
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Re: 380 ci sbc bending exhaust valve

Post by gsbrown83 » Tue Jun 04, 2019 7:53 am

I have a big low oil pressure light. Oil pressure always good. He has had bearings out of the bottom and says they still look new

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Re: 380 ci sbc bending exhaust valve

Post by fdicrasto » Tue Jun 04, 2019 11:48 am

As already mentioned, some valve stem seals are too efficient, especially the perfect circle style teflon with a flat coiled spring around the top making the seal to valve stem tension too tight. I always removed that top spring and guide overlubrication was never a problem. I now prefer the viton seals such as offered by Comp Cams. Some old schoolers still like those all teflon ones. And yes, left turning circle track stuff with out top oiling can momentarily deprive that bank of oil in some cases.

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Re: 380 ci sbc bending exhaust valve

Post by F-BIRD'88 » Tue Jun 04, 2019 12:01 pm

Piston valve relief -ex valve radial clearance on that bank.
Exhaust valve seals too good. Try removing them. Or change the ex to just those crappy black umbrella seals.
So the ex valves get more oil. What do the intake stems lok like? What is the guide/stem clearance on all?

The factory oem valve covers had drippers to drip oil on the rocker/spring. Can you add something like this to the valve cover? Springs should last longer too.
Seems with tall valve covers the oil goes everywhere except where needed.
Last edited by F-BIRD'88 on Tue Jun 04, 2019 12:06 pm, edited 1 time in total.

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