Chronic tight valve...

[norustscott]

I have a quick question. I have a 2.0l type four. The heads have new guides and exhaust valves, the cam and lifters are new and the rebuild has about 5K. When the valves are adjust correctly I have about 145psi, 150, 150, 145...1234 compression.

The intake valve on number four continues to tighten up after about roughly 100 miles. Tight to the point that the valve is open by .001+- when hot. A hot compression test yeilds 40lpsiThe original adjust is set @ .006 cold. ths has now cycled three times. I calculate that the rest position of number 4 intake has changed at least .004 to .008".

I have not checked the alignment/level on the valves under the cover yet (straight edge test) to see if the seat is working "into" the head or that the Valve has tuliped.

Question? Valve seat going away? Valve stretching? should I continue to drive and adjust with the chance it may stop?

I guess I am looking for a logical answer to why? and why only on one cylinder? and the Intake to boot.

[John Rogers]

The easiest thing to check is the cam card to see what it says about adjusting the valves. Most are done cold, but my race engine says "HOT" since I am using chrome moly racing pushrods, etc. Other things could be the valve is stretching and this can be checked by measuring the top of the valve stem to see if the measurement changes? The seat could be sinking into the head , it may not have been pressed fully in when the heads are done. Good luck.

[norustscott]

Thanks John,

I should add that the engine is bone stock with FI. From the Cam to the lifters. I do adjust cold and did experiment with the the .006 to .008 adjust on the exhaust. .006 on the exhaust has been fine.

The Seats are of unkown age. could be original. when "checked" they showed no signs of movement.

So do you keep going hoping that it will stop? Or is it time to pull and disasemble for the third time this year...

Ah, I long for the days of pulling a t1 in an afternoon, assemble a top end rebuild, and install in time to go cruising...and the damn beetle would out drag the teener... I should have never driven a 914... go fast and turn.....

[Dave at Pelican Parts]

I'm thinking it's time to pull the heads again...

--DD

[Jake Raby]

I think you are gonna have a dropped valve REALLY soon.

Don't trust this, eith the seat is moving or the valve is stretching, pull it apart or you'll have alot worse problems really soon.If were any cam problem it would also be present on #2 as well.....

Off come the heads, who built them last time?

[norustscott]

I would rather not say who until I know for sure. The advice from the shop was that the seats had no signs of failure ... better off to leave them alone. It was not a matter of being cheap. I would have gladly paid to remove and replace all of the seats, 250 would be worth it.

I actually had asked Jake if he would do head work alone. He graciously declined... I understand this would impact his motor production schedules.

With Jake and Daves comments I am going to have to park it in the garage....and Fall is just about the best time to drive here in Maryland.

I will yank the the engine and give a report.

Thanks, Scott

[pbanders]

Originally posted by Jake Raby
I think you are gonna have a dropped valve REALLY soon.

Don't trust this, eith the seat is moving or the valve is stretching, pull it apart or you'll have alot worse problems really soon.If were any cam problem it would also be present on #2 as well.....

Off come the heads, who built them last time?

Question - isn't it unlikely that a valve would "stretch", unless it was in ductile failure (e.g. perhaps heat related, and outside of the elastic zone)? Has anyone ever measured "valve stretch"?

If the seat is moving, wouldn't it move in such a way that the valve would get looser, not tighter?

No criticism here, just trying to understand valve failure mechanisims better.

[Ron Meier]

The valve spring pressure is against the head and the tip of the valve. The spring is compressed in the rest state to provide sufficient seat pressure to "close" the valve. As the spring is compressed further, the rate goes up so that the lifter will follow the cam profile.

A valve "stretches" mainly at the interface of the head and stem by spring pressure on the seat. The seat is being pulled into the head port by spring pressure on the seat.

The preset "lash" will close up as the spring installed height becomes greater as the spring pulls the valve apart or pulls the seat into the port.

Lots of aluminum flying when one or the other comes apart (for a moment anyway).

[Dave at Pelican Parts]

You are correct about the valve stretch. In general, it occurs right before the head of the valve pops off and bounces around inside the combustion chamber. Which is right after the valve undergoes ductile failure...

Seats can "recess", or "get pounded into the head". I'm not sure of the mechanism, but I've seen one or two. This is usually followed by the seat coming back out of the head again.


Hmm, I did think of one thing that might not be a sign of impending motor failure: How sure are you that the adjuster wasn't backing off on its own? Is the jam nut tight? You might mark the rocker, the adjuster, and the jam nut with a paint pen (hit them with brake cleaner and dry them off first!) and then drive for a little bit if you want to check for this possibility.

The downside being, it's risking one of the more catastrophic failure modes noted above....

--DD

[Zeke]

Dave, I know you know what you are talking about. But, I'm trying to comprehend the adjuster nut loosening and the adjuster screw tightening at the same time.

[Jake Raby]

Nothing destroys an engine worse than a dropped valve. Many times the waste the entire engine, including crank,rods, and even the case.

When the seat moves or the valve stretches both decrease the valve clearance as the movement is toward the rocker arm, as the spring tension is constantly applying tensionin that direction..

Hey, I wish I could have helped you with the heads, but I have to keep my heads for our engines, we barely can keep up with the demand for heads as is........You would not want to buy them individually anyway, they are like gold to me and my product....and the one thing that separates "Us from them"

[Dave at Pelican Parts]

Dave, I know you know what you are talking about. But, I'm trying to comprehend the adjuster nut loosening and the adjuster screw tightening at the same time.

Seems pretty unlikely, don't it? I certainly think so. But it is one more point where something like this could conceivably be occurring, and since it's not that difficult to check (paint marks) I think it might be worthwhile to look.

If that's not what is happening, Scott has lost maybe a half-hour of time verifying that. If it is somehow happening, we may have saved him a tear-down... Like I say, always check the cheap & easy things first. Even if they are low-probability.

--DD

[norustscott]

After 25 years of adjust valves I feel confident that the adjuster is tight and not moving ( Hey I wore out a .006 feel gauge! now .0055")

I must confess that the first thing I did was doubt my adjusting skills. But have have done this 100 mile cycle three timeswith teh same result and it is only with # 4 intake valve. I even went so far as to replace the adjuster screw...no change. I could only be so lucky...hey remeber the type 4 formula: Take the effort, the cost, or the availibilit of a type one part/repair and mulitply by Four>>>

So lets say I have pulled the sucker apart and I am looking at a bare head with seats in place. What do you look for? Other than the obvious...cracks, movement and depth... I guess I could measure the valve as well.

Is there a new process or seat material I should investigate to keep the seats in place?

There is a guy on the east coast that runs a t4 altered drag car. "CHUCKLES" big motor, Turbo, EFI, two speed powerglide...get the picture One summer he dropped a valve seat almost every other race. HE mentioned that a "new" process was developed and his seat problems went away? any thoughts?

[Jake Raby]

Different seat maretial, and more interference fit and cryogenics have keep me from dropping a single seat since 1997, not one...And I have averaged atleast 50 TIV engines per year since then...even when severely overheated they won't drop, even with huge valve spring tensions...

[norustscott]

Good evening,

I just retured form the garage. My findings... well...

...My saga continues

I recently had the heads back off and sent to Rimco for new seats and guides. (The reason for the head work was the intake valve on number four would get tight after 100 mile. In the 100 miles I would loose .006 " in that period.) see original post.

Well, the heads are back on and I have put about 350 miles on the engine. I have adjusted the valves four times in that period. Most of the time I found them within .006-.007".

Last week I did experience a rough idle. I did a compression test and found number four intake had 90 psi. 1,2,3 had 155psi. Sure enough the valve was too tight.

Yesterday, on the drive home from work, the 2.0l started to run very rough. Again, plugs out and I headed straight for number four intake. Compression test.....ZERO on number four.

Tight Valve! You have got to be kidding!!! This is crazy.

When I shipped the heads off to the RIMCO, I indicated the problem with number four intake. They confirmed that it could be one of two things. Vavle seat going away or a valve stretching. They checked for both. they replaced all of the seats and checked the valve...vale was reused.. .They did replace the intake guides...they had about 1200 miles on them from the first head fresh last year.

My fear is that RIMCO missed some fatal flaw in the head. A crack? They did find three plug bosses with cracks and I had them weld them up. The heads where completely bead blasted and very clean. I think it would be hard to miss a crack.

So, has anyone had a problem like this? 25 years of type 1 never created a problem like this.

I have not contacted Rimco yet. I think I know the anwer"...oh really. Send it back and we will check it again..."

What are they checking for? ... I have heard that aluminum, like other metals, could collapse with age and distress. has anyone experienced this?


I appreciate your comments and possible direction....

Regards,

[Jake Raby]

take that head off and find the problem before you lose the entire engine. It sounds like the valve is stretching more than anything else, even the best valves can have defects.

it is time for disassembly! Valves DO NOT play, email me if you want to see the proof of what a valve can do when it drops all of a sudden into the chamber. NOTHING is worse in the failure dept than a valve, I would rather spin a bearing as drop a valve, atleast you can watch the oil pressure drop before that happens.......a dropped valve is as silent as a massive heart attack, until it happens, then you really know it happened!

[Conrad W Peden]

Ooooo! Silent but deadly.

Sounds like my Mexican lunch.

LOL

[Dave at Pelican Parts]

A few other things to check--

1; Check the valve adjusting lug. How does the face of it look?

2; Check the pushrod. Is it straight? Does it look OK? How does the length compare to the others?

3; Check the lifter. This means pulling the pushrod tube for that valve out of the motor, but you'll have to do that eventually if you pull the head, right?

While you've got the lifter out, see if you can take a look at the lobe on the cam.

Note that cam/lifter problems are unlikely as only one cylinder is being affected, not the two on the opposite sides.

--DD

[JWest]

I was thinking that (lifter) Dave, but trouble with the cam or lifter would show up as a looser valve, not tighter. As Jake had mentioned, the cam will show up on the #2 intake as well. A failure of a single lifter on #4 intake is a remote possibility, but would still be a looser rather than tighter valve.

I would have to guess a stretching valve or receding seat, as strange at that would be after being examined by RIMCO.

[norustscott]

Well, Despite the fact that it is the wifes birthday today. I think I am going to drop the engine tonight, strip down to the long block in the AM. Hey we have 8" of fresh snow...and 1/2" of fresh road salt...the 914 is not leaving the garage anytime soon.

I figured that I will be replacing all of the intake valves this time, the sodium exhuast are new.

How do I check to see if the seat is receeding? Lets see. If my logic is correct...the seat or the valve has moved/stretched...drum roll please...between .006-.010" I base this on the number of times I had a rough idle, checked compressionon number four, and found it low...95+- psi. The last time I found Zero psi. I firgure that the engine at operating temperature would grow to take up .005" of the .006" valve lash. If it is proped open enough to leak yet maintain 95psi, I would be looking at roughly .002" o stretch or seat reduction. This happened three times before the heads went to RIMCO and twice after. The final time I had zero psi. My thought is that it would have to be open at least .004" to have zero resistance and record a compression measurment of zero.

So, 2+2+2+2+5=.009" maybe more???

Can a valve stretch that much without breaking? I guess I can take the digital calipers, measure and compare against the other intake valves?

It there a specific spec. on the length of the valve? Would RIMCO have install all of the seats @ the same height in the combustion chamber. I could use the dail indicator to pick up a variance? Is that sound logic?


thanks, Scott