differences between 69 and 70 3927186 heads?

[Joe L.]

Re: differences between 69 and 70 3927186 heads?

here's a couple of pictures of my broken heart......

The valve head broke off from the stem. Spring, retainers etc were still attached, but the head of the valve went for a wild ride. Interesting in that I put a torch on the heat riser valve spring and it opened immediately. But it definitely wasn't opening on a hot enging. It will be replaced and wired open for non judging. I can't think of another reason this would happen and it seems too much of a coincidence that it would be the cylinder right above the heat riser.

[ATTACH=CONFIG]124309[/ATTACH][ATTACH=CONFIG]124310[/ATTACH]

Richard------

You mentioned earlier that the engine is an L-46. You also mentioned that it was completely rebuilt. Was it rebuilt with 300 hp "flat top" pistons because that's what you have?

[Richard R.]

Re: differences between 69 and 70 3927186 heads?

well, I didn't expect that. Pistons are forged federal sealed power LW-2256f 40. The builder selected them. Engine pulled (multiple) 400HP on the dyno with the wrong (undersized) carburetor. Not a stroker, but we did use a roller cam and roller lifters.

Joe, what should I have used/use?

[Joe L.]

Re: differences between 69 and 70 3927186 heads?

well, I didn't expect that. Pistons are forged federal sealed power LW-2256f 40. The builder selected them. Engine pulled (multiple) 400HP on the dyno with the wrong (undersized) carburetor. Not a stroker, but we did use a roller cam and roller lifters.

Joe, what should I have used/use?

Richard------


Original L-46 pistons were "pop-up" style and produced an advertised compression ratio of 11:1. The pistons you have may well be the ones you mention. However, they have a "flat-top" configuration like the 300 HP pistons used for 1969-70. As such, I would expect they would produce a compression ratio similar to the advertised 10:1 of those engines since the combustion chamber volume of 300 HP engines and L-46 was about the same. Of course many factors can affect final compression ratio such as head surfacing, cylinder overbore, gasket thickness, etc. Your engine builder probably selected these pistons to reduce compression ratio in view of current gasoline and the fact that likely head surfacing and cylinder overbore would have the affect of increasing compression ratio. I do note, though, that composition head gaskets were used rather than original style shim gaskets. The composition head gaskets would have the effect of reducing compression ratio.

[Richard R.]

Re: differences between 69 and 70 3927186 heads?

here's a better picture of #6 cylinder. Hard to tell if the stem broke or was melted since it was beat up pretty bad. The shop that has it now is a different shop than did the rebuild. I moved during the restoration and this shop seems to know it's stuff. But then again, the last one did too....

On my next trip to the shop, I will take a few pictures of the disassembled engine. Specifically the pistons and the broken of valve. piston.jpg

[Leif A.]

Re: differences between 69 and 70 3927186 heads?

here's a better picture of #6 cylinder. Hard to tell if the stem broke or was melted since it was beat up pretty bad. The shop that has it now is a different shop than did the rebuild. I moved during the restoration and this shop seems to know it's stuff. But then again, the last one did too....

On my next trip to the shop, I will take a few pictures of the disassembled engine. Specifically the pistons and the broken of valve. [ATTACH=CONFIG]124330[/ATTACH]

Are those cracks at 2 o'clock and 5 o'clock in the cylinder wall?

[Patrick B.]

Re: differences between 69 and 70 3927186 heads?

well, I didn't expect that. Pistons are forged federal sealed power LW-2256f 40. The builder selected them. Engine pulled (multiple) 400HP on the dyno with the wrong (undersized) carburetor. Not a stroker, but we did use a roller cam and roller lifters.

Joe, what should I have used/use?

[David M.]

Re: differences between 69 and 70 3927186 heads?

I see a hell of a lot of rust for such low miles.
Was there straight water in this engine?
Did it sit for a while?
Is there a possibility this engine froze?

The head gasket exhibits liquid creep around #6 seal ring.

The pix also look like the valves kissed the reliefs in all cylinders? Could just be the pics. I blew them up but it blurred/pixelated.
Whats the 1 3 5 7 side look like?

Interesting failure. Certainly requires full disassembly.

I be interested in final calculated CR, gross valve lift, push rod length and rocker static ratio. Something is off.
Unless it froze. The valved seized in the guide and the piston sent it home.

[Richard R.]

Re: differences between 69 and 70 3927186 heads?

Yes, those are cracks in the cylinder wall. You can't see the third one from the pic I posted. The shop is going to put a sleeve in the cylinder. To them, it's a routine repair. To me, I am just glad to keep the block. On my next trip over to the shop I will get some more pics. I hadn't pulled the other head at the time, but it's all apart now. The shop didn't see anything unusual with the left side head and block. Plus there wasn't any indication the valves were impacting the pistons.

The engine was rebuilt about 11 years ago, but did sit a spell while I was finishing the restore. there was never just plain water in the block. Always had antifreeze mix. Engine was made operational (coolant, fuel lines, etc.) about 2 years ago. Other than fussing with timing and carb settings a bit, I hadn't had any other indications of something wrong.

[Mark F.]

Re: differences between 69 and 70 3927186 heads?

Bill------This is the original product, GM #1052627, the predecessor of the 88862628:

Ingredients are probably listed in highest to lowest concentrations:

• Naphtha
• 2-Butoxyethanol
• Oleic acid, ammonium salt
• Liquified Petroleum Gas (LPG)
• 4-Methyl-2-pentanol

gmpartsgiant.com has it for $11
eBay has a can on for $39.95 (OBO)

[Gary B.]

Re: differences between 69 and 70 3927186 heads?

Mark,

The killer with gmpartsdirect has always been the shipping cost. I input both a west coast and an east coast zip code and the shipping is over $70 for that one can of penetrant. Amazon sells it for $15.95 with free shipping for Prime members.

Gary

[Mark F.]

Re: differences between 69 and 70 3927186 heads?

Mark,

The killer with gmpartsdirect has always been the shipping cost. I input both a west coast and an east coast zip code and the shipping is over $70 for that one can of penetrant. Amazing sells it for $15.95 with free shipping fir Prime members. Gary

OMG, Gary !
YIKES - what a rip-off !
I've never dealt with them, so I didn't know...
thanks for the heads up

[Richard R.]

The rest of the story.....

I picked up my engine from the shop this week. They repaired the cylinder with a sleeve, replaced the pistons, valves, valve springs, oil pump etc. Kept the cam, crank, rest of the valve train. Replaced the one head that was toast with a good dated part. It is running sweet. Good oil pressure, good torque and HP. We left the flat top pistons in specifically for the fuel, at their recommendation. compression is at 10.5:1

Just as a reminder, this is an L46 original block to the car and when it was rebuilt the time before, we installed a roller cam and roller lifters.

But here's the interesting part - I have been talking to them on and off about trying to figure out what happened to it. My initial guess was a malfunctioning heat riser valve since I discovered that it wasn't opening properly, right before the engine let loose. But they couldn't find any heat related damage, anywhere. Upon assembly and initial run on the dyno, the builder noticed a slight noise and put his hand on the valve cover. He felt something that wasn't right. Removed the valve cover on the right side and noticed marks on the oil baffle, right below the PCV valve. This also happens to be above the valve that failed, #6. He removed the other side and saw the same thing although not as pronounced. He corrected the intereference with the rockers and it all appears and runs good.

His guess, which is probably correct, is the roller rocker interference caused the valve to hang and the piston hit the valve and snapped it off, causing all the other damage. The rest of the valves were fine. I don't have a better answer and since the previous shop installed the roller, I can only guess they missed the problem in the build. Which would explain also why the engine didn't last very long. They should have checked for interference and caught it. They didn't. Jerks.

I'm still going to replace the heat riser valve though. Can't wait to get it back in the car!

A couple pictures of the cleaned up piston are below.

Just though you may want to add this to the body of knowledge out there.

Best,

Rich
piston #6 a.jpg piston #6 b.jpg

[Leif A.]

Richard,
Congratulations on, what sounds like, a successful rebuild and finding the culprit. Just a thought...you said you're going to be replacing the exhaust manifold heat riser. Might I suggest that you, either, dremel the valve out of the new heat riser or use a spacer instead. If you're not driving your car on a regular basis in sub freezing temperatures, you won't notice the missing valve. Just something to consider.

[Richard R.]

Correction on what material was removed from the valve cover. I took the covers off today to take a look and you can see by the attached pictures they ground off some of the "bumps" on the underside and a bit into the cover itself. Builder told me he was pretty anxious when he did it. I thought it was on the baffle.

Leif, you're right about just removing the valve inside the housing since this is a warm weather car. I had thought about removing the valve since I was so freaked out by the mishap, but I am planning to PV this car (It blew the day before I was leaving to do that) and I want a functional valve for that. If I could replace the spring without damaging it, I may try that.

Thanks for the suggestion!

Rich
inside valve cover a.jpg inside valve cover b.jpg

[Joe L.]

Correction on what material was removed from the valve cover. I took the covers off today to take a look and you can see by the attached pictures they ground off some of the "bumps" on the underside and a bit into the cover itself. Builder told me he was pretty anxious when he did it. I thought it was on the baffle.

Leif, you're right about just removing the valve inside the housing since this is a warm weather car. I had thought about removing the valve since I was so freaked out by the mishap, but I am planning to PV this car (It blew the day before I was leaving to do that) and I want a functional valve for that. If I could replace the spring without damaging it, I may try that.

Thanks for the suggestion!

Rich
inside valve cover a.jpg inside valve cover b.jpg

Rich-----

The "bumps" you describe and picture are actually called DRIPPERS. They were used on 1969 and later original aluminum valve covers. They are designed to provide extra, drip lubrication to original rocker arm pivot fulcrums. They are unnecessary if roller fulcrum rocker arms are used. In this case, the "posi-lock" style rocker arm nuts will usually interfere with the drippers. That's not a good thing but I do not understand how that sort of interference could cause the type of problem you experienced.