Big issue from Little part...

[Knukle Head]

I've been working on my x for a while and I was just about to take my victory lap because it was all back together and running strong. (full write up with pictures) Then it happened ... on Monday after a week running strong, it started to run rough and then it cut off .. I swore I heard the piston slap a valve.. I was close to the house so I towed it back to my garage and immediately dropped the engine. .
To my surprise the timing was exactly where I left it (I checked it no less the 11times when it was installed ) This in my mind was the worst of all worlds. I didn't know what was going on and I had just pulled the motor!!! I started to question what I really heard.

I then decide to purchase I an OTC leak down tester (love this tool) and check the cylinders... Ahaaaa there was surely and issue with 90% loss in cylinder 1 and 3. Further investigation showed me that the issue was the last intake valve on cylinder 3 and the exhaust valves. (Not sure which one) Cylinder 1 was just leaking from the exhaust valves (not sure which one).

So I know knew there was an issue but I had no idea why.. timing was still perfect (((head scratch)) I start the process of digging down to the head and I find IT!!!!! A little barrel shim laying in the upper rear timing belt cover... I immediately know where this goes and what caused the problem..

On the back of the cam pulley there are these little barrel shims. My shim had come out and it allowed my cam to turn independent of the cam pulley. I did in-fact hear contact, I'm not crazy...
Now, I will continue to remove the rear bank head and see what the true damage is.. (fingers crossed)

Here is the million dollar question for anyone with knowledge.. What was supposed to keep those shims in the back of the cam pulley?

To be continued>>>

 

[OLDMNSX]

Gene,
Sure sorry to hear of your misfortune. Do you see the part in question in this parts diagram of the cams and gears?
http://www.dchautomotiveparts.com/a...l-engine/engine-cat/camshaft-timing-belt-scat
I'm a visual kind of guy. I've got to see a picture, but it sounds like a bent valve or two.
Brad

 

[Knukle Head]

In the diagram you referenced it shows as a little dowel pin or (key)on the back of all the pulleys .. when you install the cams the "key slot" should face up .. these keys slide half way into the pulley and half way into the cam key slot so that the cam and pulley stay together.. I'm sure I have some bent valves, I just need to know how to keep those keys in place so this does not happen again..

As a follow up question, in a case where there are bent valves is it likely new valve guides will be needed or should I just inspect?

- - - Updated - - -

Happy
I will give a full write up once this latest issue is addressed..


Great tool

Yikes....

Used rubber gloves to detect where the leak was coming from (intake exhaust rings)



This is what a leaking intake valve looks like using the "glove" method..


On the back of these pulleys there is a small key ...


The culprit!!! (placed on the frame and not really focused )

 

[OLDMNSX]

Gene,
The key is called a "Half Moon Key". It is captured in a machined Half Moon slot in the cam. The cam gear key way is straight cut to slide over the key and keep the key from escaping. It is very easy to dislodge the half moon key when installing the cam gear. After installing the gear look down the key way with a light to insurer proper installation of the key before installing the gear retaining bolt.

Valve guide damage from the bent valves is possible, but not likely. Wear may be a problem though. Be sure to inspect the "Lost Motion Assemblies" for normal operation while you have the head apart.

Hang in there "Knuckle Head"
Brad

http://www.scienceofspeed.com/products/engine_performance_products/NSX/ScienceofSpeed/LMA/

 

[Knukle Head]

Here is the damage

I still find the retaining method for the keys interesting because it seems like the "keys" are short enough to work their way out.. here is a shot of the front head Keys still in place..


Looks like the cams put up a fight before letting the keys go..


If I buy all new valves will I have to resurface the valve seats ?
Would used valves on the damaged cylinders be risky?

- - - Updated - - -

Almost forgot this shot of the pistons which look fine to me...you can clearly see where there was contact on cylinder 3..

 

[davidf]

I'll say this. It's not my money but I'd really consider replacing the Lost Motion assemblies since it's this far down. Sorry about your misfortune. Oh, and some headers. Let that thing breathe.:wink:

 

[Knukle Head]

Thank you for the words of encouragement gentlemen.. I actually have the lost motion upgrade from sos ( I'm spoiling my soon to be build thread)

The header issue is sooooo tough for me..
Money is not unlimited and I am saving up to purchase the pride v2 exhaust (love love love the sound)... Since the Pride is restrictive, I figured there was no point in getting headers to just restrict the flow at the exhaust ..

But hate the factory headers, every time I see them I second guess my choice.

 

[davidf]

I'd take advantage of the "OBO" statement. Very decent headers.


http://www.nsxprime.com/forum/showthread.php/185015-SOS-Headers-great-shape

 

[OLDMNSX]

Gene,
Here is the thought on your question New or Used Valves? 1. Are you going to do a complete valve job on both heads or just repair the damaged valves? 2. Are you going to do all of the valves on just the head with the damaged valves, or just fix the damaged valves? 3. Do you have some used valves? You will need to fit either new or used valves to the seats.

Maybe someone out in NSX land has some good used valves for you.

A complete valve job can get VERY expensive! Have you checked the other cam gear keys for proper installation?
Brad

 

[Knukle Head]

I was just going to repair the bent valves, so I bought used valves from a prime member.. In order fit the used valve to the seat, do I need to take the head to the machine shop, or is this a process I need to research myself..?

 

[OLDMNSX]

Gene,
I would take the head and valves to a machine shop to look at them and then do what is needed. I would guess that they would grind the valve and seat to make a good seal. Probably replace the valve stem seals too. Everything else should be useable. He may want to surface the head to, or at least make sure that it is true.
Brad

 

[Knukle Head]

I just had the head surfaced so I think I'm prob good.. I talked to some race specialist and they said I should "lap" the valves on my head .. They told me how to get it done my self ...whooot!!!!
Gentlemen, I will be lapping the valves as soon as they arrive!!!
Dare I hope to be on the road this weekend.. ... <-- shhhhh I cant say this its too fragile...
As far as those keys are concerned, they will be installed with a very minute amount of JB weld.

 

[Old Guy]

I have never done this on an NSX (and don't ever want to be in the position of doing it!); but, I have done it on other engines. Lapping is usually a 'final fit' activity and as such you cannot have any damage to the valve mating surface or the seat. If you do, then its off to the machine shop to have the seat refaced. The valve guides also need to be in good shape, otherwise your lapping may end up being non concentric around the axis of the valve. Since you are installing used valves, check the diameter of the valve stem to make sure that it is within service limits and unless you are confident in their history, I would also have a machine shop check them to make sure they are straight. If the replacement valves check out, then with the valve inserted in the guide, use a dial gauge to check for excess lateral movement of the valve stem. If all of this is good, then you can proceed to the lapping / final fit of the valve.

If the valve contacted the piston, I would really want to be sure that the valve guide was not damaged in the process.

 

[Dr. JL]

I would not recommend valve lapping. New engine valves are not lapped from the factory. My Local performance shop machinist told me he's repaired many heads from folks trying to save a few hundred bucks by lapping valves. He had a grin on his face when he told me this.

 

[JD Cross]

Have never been in this area in my engine so would like to learn some things here before I go in there in the future.

Is the slot machined into the end of the camshaft tapered in any way to keep the key from backing out of the cam gear?
If it isn't what keeps the key from backing out?
If the key isn't fully inserted into the cam gear pulley does the key still lay flat in the slot allowing you to bolt on the cam gear?

In the pic of the end of the camshaft it looks like some metal was torn/abraded from the left side of the key slot.
What would cause this?

 

[Old Guy]

I would not recommend valve lapping. New engine valves are not lapped from the factory. My Local performance shop machinist told me he's repaired many heads from folks trying to save a few hundred bucks by lapping valves. He had a grin on his face when he told me this.

Agreed; but, on a rebuild it depends on the skills of the machine shop. If after the repair, a test with machinists layout blue shows a nice even contact band around the periphery of the valve , don't mess with it. Tiny variations may be cleaned up with lapping. If there are significant variations in the width of the band then its back to the (to a different!) machine shop. Lapping is definitely not a repair technique and it is admittedly a bit 'old school'.

- - - Updated - - -

Have never been in this area in my engine so would like to learn some things here before I go in there in the future.

Is the slot machined into the end of the camshaft tapered in any way to keep the key from backing out of the cam gear?
If it isn't what keeps the key from backing out?
If the key isn't fully inserted into the cam gear pulley does the key still lay flat in the slot allowing you to bolt on the cam gear?

In the pic of the end of the camshaft it looks like some metal was torn/abraded from the left side of the key slot.
What would cause this?

Typically, gears or sprockets mounted on a shaft are positioned by a woodruff key which locks the position of mating slots on the shaft and the hub of the gear / sprocket. The Woodruff key is half moon shaped which fits into a half moon slot on the shaft. The half moon shape prevents the key from moving axially on the shaft and is typically kept in place by being completely covered by the hub of the gear / sprocket.

In the third picture in post #4 , it looks like the back half of the slot on the end of the camshaft has the half moon shape of a Woodruff key. In a normal Woodruff key installation the slot would be curved up at both ends of the slot preventing any axial movement of the key. Clearly the Honda design is not like that. Also, Honda refers to the locators as dowels rather than keys and in the photos they do not look like a woodruff key. My initial reaction was that because the key / dowel was exposed on the back side of the gear hub, the hub was probably not seated properly allowing the key / dowel to pop out. However, given the unconventional nature of the slot and the key / dowel arrangement I think my initial reaction is probably incorrect. From looking at the service manual and the photos, it is not clear to me how this should work. You need somebody who has pulled the cam gears off of an NSX engine to advise on the proper assembly.

As a matter of interest, when this was first posted, I dug my shop manual out of the car to see if it provided any specific instructions around assembly of this particular part. I didn't find anything.

 

[JD Cross]

In a normal Woodruff key installation the slot would be curved up at both ends of the slot preventing any axial movement of the key. Clearly the Honda design is not like that.

My experience with Woodruff keys, albeit in sawmill machinery not cars, is that the slot is always curved up to prevent the key from backing out or the key is long enough to fill the slot almost completely. In either case the key is prevented from backing out.
It's most unHondalike to allow a condition where the key(dowel) could back out enough to allow the pulley to spin free.
I've not heard of this happening with any frequency before.

I noticed the OP's pulley are painted blue and the key has some blue paint as well.
Perhaps he could comment on whether these are painted oem pulleys and key or aftermarket pulleys and key?
In pic #8 in post 3 we can see how short the key is and in pic 2 in post 5 we can see how the key has plenty of room to back out.
Puzzling design from Honda.

Hopefully someone who has worked on this area can chime in.
If this design is standard then all of us have exposure to this key backing out.

 

[Old Guy]

I noticed the OP's pulley are painted blue and the key has some blue paint as well.
Perhaps he could comment on whether these are painted oem pulleys and key or aftermarket pulleys and key?

If this design is standard then all of us have exposure to this key backing out.

I also noticed the blue pulleys and was thinking bad aftermarket parts; however, the pictures in the service manual of the stock pulleys suggests that they are just painted stock Honda parts.

I doubt that there is a design issue. I am still thinking some kind of assembly issue.

 

[Kaz-kzukNA1]

I was in the middle of writing something for the aftermarket header/coolant tank in another thread but it will take hours and another member wanted some advice for this post so decided to finish this one first.....

Out of about 7,000 NSX in Japan, I never heard of valve damage caused by this guide/dowel pin backing off.
Even without the pin, if the cam pulley was seated properly and if the pulley bolt was tightened to the spec, then I think it will take long time before you start seeing even a small loss of torque at the pulley bolt.
In order to cause valve damage, the pulley needs to be fairly loose allowing the camshaft and the pulley to rotate at different timing or the camshaft to stop somewhere pressing down on the rocker arm while cam pulley rotating.

The camshaft on alone can't spin by itself.
As the OP experienced the issue just 1 week after working on the TB area, I'm afraid I can't ignore the possibility of installation issue.

Ideally, I wanted to wait before posting here until after I measured the length of the guide pin and the amount pressed inside the pulley body but for now, I'll post the camshaft side first.
As you can see, it is very unlikely for the pin to be able to back off far enough to dislocate itself from the pulley.

From the photo by the OP showing the damaged cut out (slot), it looked that somehow the pulley bolt got loose (pin still held inside the pulley and very likely to be in its original position), pulley started to rattle, at some point the rattle was big enough allowing the pin to wedge itself just at the upper side of the cut out (slot) on the camshaft, eventually the force was enough to allow the pin to climb over the cut out (slot) resulting in wrong cam timing (started to feel rough) and eventually the pin got dislodged resulting in engine shut down due to completely wrong timing and vent valve. The cut out (slot) was damaged during this process.

The OP wrote that his TB (cam pulley markings) was still at the same timing as where he left before so I believe the TB itself didn't jump a tooth hence the only way to damage the valve is to disintegrate the link between the cam pulley and the camshaft timing and that can only be done by the loose pulley bolt.

I'm in the process of Eng Refresh for another owner so hope I can measure the length of guide (dowel) pin and also the length held inside the pulley body.
Above photos are from my engine so several years ago.

As a side note, the pin can't go the other way round (TB middle cover side) as it's blocked by the big washer of the pulley bolt.

Kaz

 

[JD Cross]

Thanks for the clarification Kaz. You've answered the OP's question.
Can see with the tapered slot in the camshaft that if the pulley is installed and torqued correctly there is no possibility of the dowel working itself out.

 

[Mac Attack]

From my engine rebuild, I had a few observations on the OEM cams and pulleys:

1) I never tried to pull out the dowels from the pulleys, but they looked like a nice tight interference fit. Like Kaz said, they are constrained on the other end by the bolt washer.
2) It seemed like there was enough "play" in the dowel and tapered camshaft slot that the pulley could be rotated about +/- 0.5 degree... so there is a little bit of wiggle room radially. IIRC, the torque on these bolts is about 60ft-lbs, so they are nice and snug!

I have two hypotheses why the above happened:

1) Like wheels and the interfacing lug nuts, never paint on critically-torqued areas. When you torque something like this down to 60-80 ft-lbs, the paint has already chipped and the head friction is not there. Unless you masked off the gear retaining bolt head seating area before painting, then "untorquing" would occur when you decelerate the engine with a load on it (why that particular area on the rear bank intake cam key is worn). How tight was this retaining bolt when you took the pulley off? Just a little loose will put a lot of cyclic stress on that little pressed-in dowel pin and eventually loosen it up.

2) Did you try to remove the dowels when the cam pulleys were painted, and if so, were they placed back into the correct depth (all the way flush on the opposite side)? If they weren't, and you torqued the pulley on the cam, then you could have bent the dowels slightly against the arc on the cams and it would be easier for them to work their way out later.

Either way, this problem most likely had something to do with painting the cam pulleys. I'm with you though - I spent a lot of time cleaning mine up after 125k miles. I even went through each pulley tooth and hand-scraped all the old TB "gunk" off so my new TB would have a nice, clean surface to slide on. You can't just take a wire wheel to them though. I assume they have some anodized coating on them so I was very careful!

While your engine is apart and if you didn't scrape off the paint underneath the pulley bolts, then I would take the time to do so.

Also, check out Kaz's excellent instructions in this thread for the correct TB tension (Thank you Kaz!):
http://www.nsxprime.com/forum/showthread.php/45564-DIY-Timing-Belt-Question/page3

 

[Knukle Head]

Thanks again to everyone who has replied here.. I sincerely hope this was an installation issue but to be honest I'm just not sure where.
I torqued the cam pulley bolts. Even stranger when I was disassembling the engine I did not note that there was a lose bolt on the cam pulley.
The pulleys are painted with an automotive enamel but it is not thick (for fear I would screw with tolerances). I suppose the paint could have something to do with this but I just don't see how ... (scratching head) they were still tight when removed..

Good news is its all back together.. the valve lapping increased my leak down to under 15% and she has been running well for two weeks ....