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Posted by: Jetsetsurfshop Apr 2 2016, 06:36 PM

On my first outing with the new engine tragedy struck. While giving it a little bit of RPM the engine made a noise I never heard before and then dropped a cylinder. Limped it home and this is what I found today.
That's the top of the valve you see still with the keeper! Damn.
Anyone have any thoughts on what happened here?
Everything we did was the same as the last build except we installed a more aggressive camshaft.



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Posted by: Jetsetsurfshop Apr 2 2016, 06:37 PM

Oh yeah
Broke the rocker arm too.

Posted by: Mark Henry Apr 2 2016, 06:59 PM

Ouch
what valves are those? Used stock? Intake or exhaust?
I see late adjusters, you shouldn't do that but that would only mash the valve stem end.
engine spec details please.

Posted by: Jetsetsurfshop Apr 2 2016, 07:05 PM

48mm intake
38mm exhaust
They are stainless steel.
We used the adjusters that the car had on it when I bought it. It was a mid build. What are you suggesting?

2258cc
44 webers
Duel springs

Old lift on cam was .465 new lift is .533

Posted by: stugray Apr 2 2016, 07:31 PM

Did you have valve relief pockets in the pistons?
with .533 you might have interference, more-so with oversize valves

Posted by: Jetsetsurfshop Apr 2 2016, 07:36 PM

We had the pistons done to fit the valve. I tested the fitment with playdoh.

Posted by: fixer34 Apr 2 2016, 08:17 PM

If that is the valve spring retainer, then you didn't have the classic valve-piston interference. It appears the valve shaft failed, probably just a little down from the retainer. Maybe a fracture or defect and the double springs plus some extra rpms caused it to break. The good news is you most likely didn't damage the piston, cylinder, or head.

Posted by: Valy Apr 2 2016, 08:52 PM

That's a lot of lift for stock adjusters. The force they apply when they start to push is too much off axis so it tends to bend the valve stem. That together with high RPM will brake the stem at the upper weakest point, where the retainers hold the valve.
I bet it's not an interface issue as that will bend and brake the valve near its head.
I would recommend adjusters that have a moving foot like the 911 ones or the ones that have a ball in their foot.

Posted by: Cracker Apr 2 2016, 08:53 PM

Bummer! I hate to see that...it IS part of the game. Hopefully the piston is fine.

T

Posted by: Mark Henry Apr 2 2016, 10:00 PM

Well Valy nailed it and it could be at least part of the reason for the failure.
.533 doesn't sound like a mild cam.

Still like to know what was the rest of the engine parts you used, specs and more pics of the damage. For one I want to see the head spring/guide boss area.

Guessing at what you have and the damage is just a waste of my time.
Asking for help, but only giving out half of the info is one of my pet peeves.

Posted by: Jetsetsurfshop Apr 3 2016, 05:08 AM

Didn't mean to be so vague. I've never seen this before and thought it'd would be a good this to post up as I fix it for future shade tree mechanics
Here's those specs (most of what I remember)
78mm crank dpr
Scat h rods
Je 96 mm Pistons with valve relief
Heads are what the car came with and there on there last leg
48 mm intake
38 mm exhaust
49 cc head chamber
Dual valve springs
Custom length pushrods
Stock valve train
Camshaft duration is 318 lift is 533 (this is from memory)
44 dual Webers

I found all these lovely parts last night and started to tear the rest down. Was going to try and remove the head from the car but the cooling tin behind the oil cooler looks like it's in the way. I'm hoping that the piston isn't damaged. We don't believe it is, but will post pics when I get there. I'm in retail and this is my season. Its agonizing to not be able to wrench but it will have to wait.
I think valy nailed it too. Sounds like new valve train is in my future.

Posted by: The Cabinetmaker Apr 3 2016, 05:48 AM

I'm confused. Bigger valves, monster cam, dual springs, custom pushrods. How is that a stock valve train?

Then you say in your first post that you only added a more aggressive cam on the last build and used the old pushrods. Do you think they were still the right length?

How many times have you rebuilt this engine?

I know this might piss you off, but I think you should have someone else rebuild this engine properly.

Posted by: McMark Apr 3 2016, 06:32 AM

I would love to see the valve train geometry before it broke.

This seems like one of those situations where we realize once again that an engine is a combo -- it's an ecosystem -- and one change can have cascading effects. I wouldn't be comfortable building an engine with that fast of ramp rates, using larger (heavier) valves that was meant to rev. If someone came to me with those specs, I would say, "Let's spend a lot of money on valve train lightening."

Is component mismatch your problem? Dunno.
Is incorrect setup your problem? Dunno.

But building an engine that aggressive takes a lot of checking and planning to get right.

When you can, post some pictures of the valve area. Maybe there's a clue in seeing the rest of the valves.

Posted by: Mark Henry Apr 3 2016, 06:40 AM

I'm guessing that the cam is a Scat C-55, way too much for that stock valvetrain.
When you get there I still want to see how the head looks at the valve guide boss.
I'd also like to see the other side with the intact rockers.

Posted by: Jetsetsurfshop Apr 3 2016, 08:14 AM

Cabinetmaker
I meant stock rocker arms. Sorry.
The pushrods are the same from the last build with the web 494 cam. They are not stock. I custom cut them then back then and they could be the wrong length.
This is my third engine, first problem like this. Not pissed at all. Its all good.

Mcmark
As far as the geometry goes, were going to look at it when i drop the engine. I kinda hurried this build to make it to a NASA event. That will teach me. I will post more pictures as I get the engine out. I will take my time now and inspect and measure. There will be clues, I'm sure of it.

Mark Henry
You could be right about the cam. When George and I did Chumpcar last year my car was a little better the a mid-pack car. I was hoping to squeeze a couple more HP out of this engine and run with the big dogs in an old ass 914. Looks like I over did it.

Time to go to work.

Posted by: stugray Apr 3 2016, 09:48 AM

And how much clearance did you have?
Just from memory you need somewhere around .120 min, but I would have to check my notes.

I was imagining the valve barely touching the piston, not breaking off.
That would cause MUCH higher forces on the valve stem at full open exacerbating a valve geometry problem and stressing the weakest point on the valve stem (where the retainer goes).

Posted by: HAM Inc Apr 3 2016, 10:18 AM

The valve breaking in that position is a classic symptom of valve float and launch and/or coil bind. With a big heavy valve and aggressive cam all of those situations can occur at the same time.

The spring may not have been in coil bind at lower revs, but a heavy valve and aggressive cam can easily put a valve in a launch condition.

What were you turning it when it let go?

I noticed in the pic that the keepers appear to butt, meaning they are floating in the keeper grooves. That will contribute in a big way to this type of failure in a valve float, launch situation.

If those are the springs I think they are they are very unsuited for 48mm valves and an aggressive cam when fresh, much less when they have some hard track miles on them. Around 15 hours of hard track time is max for them. They typically lose around 8-10% of open pressure by then.

A failure of a rocker and valve at the keeper grooves is almost certain to be preceded by float, coil bind or geometry problems. Generally all of the above happen when a major misapplication of components occurs.