380 ci sbc bending exhaust valve

[bentvalves]

give the problem ex valves .0022" clearance and go from there.

if you already have .0022" then give it .0025"

[PRH]

Measure the offending guide bores from top to bottom.

I’ve seen it many times with bronze guides where the ex port end of the guide shrinks down to almost zero clearance.
If you’re experiencing that on your heads, you can run a reamer several thou bigger than the bore diameter, from the bottom up, about .250-.375 from the bottom, as an oversized counter bore.
Or hone the bottom of the guide bell mouthed by about .001 or so.
Exhaust guides only.

With a few of the dirt motors I helped out on, any less than .0025 ex guide clearance and you’d stick a valve.

If running Viton steel jacketed seals, remove the spring from the top of the exhaust seals and make sure there’s a chamfer on the top of the guide(which acts as a little oil reservoir).

[gsbrown83]

Prh that's good info thankyou. I do believe we r chasing a guide seal issue. 4 years no issues but I need to find out tonight if he replaced the guides this winter with my original heads when the problem started. The weird part is the new heads came with guides I'm beginning to wonder if the type of seals he is using will not work or work to well especially on the left side of the motor

[Newold1]

As I said earlier, even new heads when they come out of the box should have valve stem to guide clearances checked and set to clearances decided as adequate. If the exhaust guides have viton metal jacket seals on the exhaust guides the seal spring should be removed and as mentioned here in this thread earlier its a good idea to have a chamfer at the top of the guide to allow lubricating oil to stay there and make sure the valve stem and guide remain lubricated. On 3/8" and 5/16" valve stems I like to see a minimum of .0015" on intakes to .0020" On exhausts I like .0020" minimum and .0030" maximum both of these for silicon bronze guides.

[PRH]

On the heads I was doing(brodix dirt spec heads), the ootb ex guide clearance was a nominal .0015”.
They needed another thou added to that or you had stuck valves.

[gsbrown83]

It's dropped back off at builders I'll know more tomorrow let me ask you guys this. Being a dart little m block is there anything block related oil galley or etc that could be causing a shortage of oil to top

[gsbrown83]

^
Lack of oil to the left side mainly is what I meant

[af2]

http://dartheads.com/dart-product/little-m-sbc-iron/

Go to the Tech sheet.

Read up because most people don't understand the oiling..

[fdicrasto]

OEM blocks(sbc) usually required lifter gallery restrictors but the aftermarket stuff does not need restrictors. I have seen instances where a builder made the mistake of utilizing them and caused oil starvation issues up top. Doesn't seem likely in your case but just a heads up.

[makin chips]

Prh that's good info thankyou. I do believe we r chasing a guide seal issue. 4 years no issues but I need to find out tonight if he replaced the guides this winter with my original heads when the problem started. The weird part is the new heads came with guides I'm beginning to wonder if the type of seals he is using will not work or work to well especially on the left side of the motor

What were the original heads? Same thing you replaced them with? Or something completely different? That's not been made very clear. Thanks.

[gsbrown83]

I had dart steel 215cc heads and they were replaced with 235cc.

[modok]

Steel
SO, what's the clearance?

[JoePorting]

Check your pushrod to valve cover clearance. Sometimes the valve cover will bind on the pushrods, especially with big long shaft rockers.

[Schurkey]

it has bent exhaust valves on 1 3 7.

Always #7. Then #7 and #1. Now 7, 1, and 3. Things seem to be getting worse instead of better.

Any chance there's an obstruction in the cooling system leading to localized overheating? Someone forgot to remove the core plugs after pounding them in? Head gasket doesn't have properly-located or properly-sized holes connecting block and head?

What intake manifold are you using? Single-plane or dual-plane?






Have you considered running the engine 20 laps, and then inspecting it BEFORE the valve(s) seize?

[Krooser]

Ditch the exhaust valve seals... Old Indian trick.

Seriously... I read that years ago. My engines (351C) never seemed to miss them. I was running a dirt sportsman car... 6500 rpm...

The 388 SBM I'm working on won't get exhaust valve seals either.