Bent valves!?!?

[MRacer]

My '96T is in the shop again for some engine and TCS light warning. The dealer diagnose the car for several days ow and have come down the to the conclusion that I had low compression on pistons 4 and 6. Value 4 had compression at 104 while value 6 was at 64. They suspect these values might either be bent due to high revving or burnt, but they will know for sure when they open the engine head. If the values are burnt then my extended warranty will cover the cost of parts and labor; otherwise it'll cost me 1.7k just for the labor to open it NOT including parts. They suggest it might be in my best interest to just get a new engine instead.

As for their comment about the high revving this past weekend my friend did rev (actually missed shifting from 3rd to 4th going at triple digit speed) and the engine grinded pretty hard. But the engine like didn't come on until the next evening. So I’m suspecting it might be some bent values but I’m not a mechanic so I don’t really know.

I have until next Tuesday to decide what to do. So I’m begging everyone “what should I do?”

-tm

 

[matteni]

Sorry to hear this.

If I were you I would get a second opinion. Perhaps you could ship the car to one of the west coast places like Mark B's shop? Round trip shipping or towing might cost $1000 but in the long run you would save money and get much better information / results IMO.

Question - when you say your friend missed a shift from 3-4 do you mean he put it in 2nd instead of forth? Just curious...

------------------
Nick M

91' Red/Black with Many Mods
99' Honda Odyssey with Many Kids

 

[nsxtasy]

As I recall, one of your two dealers in town is reasonably qualified, according to Chris of SoS. If you need a second opinion, ask Chris where else is competent; certainly you need not go any further than Morgan at Acura of Portland (180 miles), but there may be another one close by. There is absolutely no need to ship your car across the country to get it fixed.

Mis-shifting (to second instead of fourth) and overrevving as a consequence can indeed cause bent valves.

If your engine is hosed, I would NOT recommend getting a new engine (~$18K). You should be able to get a used engine for no more than $5K, perhaps even less. Try ERZ Motors. Chris may even know of one in your area.

 

[MRacer]

I was observing his shifting and I'm sure he shifted from 3rd to 4th. However, I'm not sure if he stepped on the clutch all the way down. That's the only thing I can think of. Now I'm regretting letting people drive my car...

I'm going to call the other dealer and check out their price for checking and fixing the values.

-tm

 

[sjs]

Man, that's a shame. I take it that the grinding you heard was the transmission gears (not the engine). That combined with your other descriptions makes me suspect he missed the up-shift so badly that it never got in 4th and he over-revved it by getting back on the throttle while it was still in neutral or while the clutch was in. The rev limiter should have protected the engine under those conditions but I have never tempted fate by proving it at WOT in neutral.

Having two cylinders that low on compression should immediately cause a pretty obvious loss of power and probably alter the sound. Could you not tell any difference?

The good news if the diagnosis is correct it was probably a light tap or the compression would be even lower, so the pistons may have nothing more than a ding in them and the guides should be OK.

How many miles on the car? If you haven't done it already, pay the extra to do the timing belt while you’re at it since it comes off to do the valves. Since the intake also comes off it makes the thermostat and some of the coolant hoses simple to replace so it might be tempting to dl those as well. If you decide to do any of those, make sure you don’t get charged "book rate" on them as if they were done separately. The whole point is that they will require very little extra time since it's already apart.

 

[sjs]

BTW, a guy on ebay has been trying to sell an engine claimed to be from a 2001 w just 3k miles on it, and it is listed again. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1853765463

His buy it now price is $10k, which is too much IMO, but he may be getting anxious to sell. Still probably not your best option unless your's already has a lot of miles on it, but something to consider for a very fresh engine.

If you consider it, I'm sort of collecting engines and would give you up to a couple grand for your old one with the bent valves. I may have someone try the liners and reinforcement work on a 3.2 but don’t want to use the low mile one I have.


[This message has been edited by sjs (edited 24 August 2002).]

 

[MRacer]

Yes, I CAN feel the loss of power. It felt just like two months ago when my oxygen sensor went out the car vibrated on and off like some the spark plugs were not firing correctly. I have a Mazada 929 with two burnt spark plugs and it vibrated funny. So I know the feeling.

My engine has 67k miles so it's too early for an engine transplant. Worse comes to worse I'll just haul my car to my cousin in Portland and have him fix it. (all it's going to cost me is a beer and a pat on the back...)

-tm

 

[Chuck]

I would not replace an engine that had bent valves. You could go to the extream and go with the Comptech upgrade or just replace the bad valves and related parts. If you have to replace pistons, that can be quite expensive if done properly.

 

[D'Ecosse]

Originally posted by Chuck:
..... that can be quite expensive if done properly.

LOL! & even more expensive if done im-properly!

 

[nsxtasy]

Originally posted by sjs:
That combined with your other descriptions makes me suspect he missed the up-shift so badly that it never got in 4th and he over-revved it by getting back on the throttle while it was still in neutral or while the clutch was in. The rev limiter should have protected the engine under those conditions

I don't think so. If he was, say, at 8000 RPM in third and accidentally shifted into second, that would make the revs around 10000 RPM, which the rev limiter won't do anything for. The rev limiter only works if you start out lower than redline and accelerate.

 

[matteni]

I have accidently tested the rev limiter many times and I can say with all certainty that it works as advertised - albeit a little higher then stock with my Dali chip.

 

[NSX TT]

Originally posted by MRacer:
Yes, I CAN feel the loss of power. It felt just like two months ago when my oxygen sensor went out the car vibrated on and off like some the spark plugs were not firing correctly. I have a Mazada 929 with two burnt spark plugs and it vibrated funny. So I know the feeling.

My engine has 67k miles so it's too early for an engine transplant. Worse comes to worse I'll just haul my car to my cousin in Portland and have him fix it. (all it's going to cost me is a beer and a pat on the back...)

If I were you.I will take the car to your cousin,those peoples are gona charge you an arm and a leg for that job.

 

[(NSX REY)]

I can't see replacing an entire motor for the problem you are having. If it is only a bent valve I would rebuilt the Top End ONLY.

As for the bottom end. If the Piston(s) were effected and had damage then replace the effected piston. The low compression may be a result of one of the piston ring(s) gone bad. When they did the compression test they could have added a few drops of motor oil into the cylinder through the spark plug hole and re-test to see if the compression changed. (Could be a broken piston ring) Don't be too quick to replace the entire motor.

Good Luck!

 

[Jimbo]

Yes, but if the valves are bent, doesn't that imply they hit something?

If valves were colliding with pistons, I'd be worried that the tops of the pistons were damaged, even if that damage might not be visible to the naked eye.

If it were my car and I had bent valves and the pistons were intact, I think I would be thanking my lucky stars that a piston didn't break and cause more severe damage.

I would then replace all the pistons, inspect the block and rods real closely, and take the time to install new rings, bearings, etc.

I'd almost rather do that than to get a used, unknown-state engine. Of course, if you could pick up a low-mileage 3.2L engine that might be another option.

-Jim

------------------
1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
http://homepage.mac.com/jimanders/PhotoAlbum1.html

 

[MRacer]

I just spoke to my cousin (he's a Toyota/Honda master tech by the way) and he suggested I asked them if they did the leak down test. This test will ping point the cause for low compression. While the compress test tests for compression it doesn't tell what/where the problem is. He also suggested I make sure they can tell me exactly what the problem is before opening this & that to prove their guesses. From our conversation it seemed like the dealer is trying to jump the gun before fully examine all possibility. If things doesn't work out, he's even willing to call and chat with their tech.

Yeah, replacing the engine is out of the question. Even for a use one. Fixing it will be the only solution.

It's a nice weekend and I'm not enjoying it.

-tm

 

[Gerry Johnson]

I would do a leak down test to see where it is loosing compression, very easy test and it will aliminate the quess work. If you have any questions E-mail me.
Gerry.

 

[sjs]

Originally posted by nsxtasy:
I don't think so. If he was, say, at 8000 RPM in third and accidentally shifted into second, that would make the revs around 10000 RPM, which the rev limiter won't do anything for. The rev limiter only works if you start out lower than redline and accelerate.

Perhaps you should read my post again. I'm not a moron, I know all about when a rev limiter will and will not work.

I stated quite clearly (I thought) that I was starting from the assumption that he was correct in his certainty that it was not an accidental downshift. Remember he mentioned grinding? That could be up or down, but grabbing 2nd instead of 4th at that speed is real hard to miss-diagnose because it is accompanied by being thrown forward in your seat as if someone hit the brakes, even if only for an instant. So in an effort to explain to him what might have occurred if he is correct, my comments were based on his confidence that it was not an accidental downshift.

As for the rev limiter, I too have put mine to the test numerous times, but never at WOT in neutral. It definitively should prevent damage, but I wouldn’t bet my engine on it. Keep in mind that it takes very little fuel to rev an unloaded engine.

I also covered the possible damage to the pistons. It is not real likely given his symptoms, but if one was dinged hard enough to have a significant dent then it might be worth pulling to have it checked for cracks. There is no reason to replace them all as suggested, at most those involved in the incident. Of course, that requires honing the cylinders as well.

A leak-down test is always a good idea, but there is no doubt that the engine needs to be opened up. Still, it would help you decide if just the heads should be pulled or the entire engine. (but if you will do both heads, the entire engine is faster anyway) The leak-down will also help you determine the overall health of the other cylinders since your going to open it up anyway. BTW, you can easily tell if a valve is bent badly enough to cause your symptoms by pulling the valve cover. A bent valve does not close all the way and will be way out of adjustment, the clearance being much larger than normal. That would also allow them to make sure it didn’t break a rocker or spring or something that’s preventing a valve from closing all the way, but given the NSX valve train design that seems improbable.

Given what we’ve heard and assuming that something did indeed break at the time of the missed shift (whichever direction), the diagnosis is almost certainly correct. Only the full extent of the damage is yet to be learned. Although I’m typically rather hard on repair shops, I don’t think these guys jumped the gun. They may not even have a leak-down tester, which may not be much of an excuse. But the point is that it’s broken and needs to come apart, starting with the valve covers.


[This message has been edited by sjs (edited 24 August 2002).]

 

[greggv]

You may also want to consider if the valve hit the piston, it could easily have closed the ring groove in the top of the piston, giving you a stuck ring, which will not be visible from the top.

 

[sjs]

Originally posted by greggv:
You may also want to consider if the valve hit the piston, it could easily have closed the ring groove in the top of the piston, giving you a stuck ring, which will not be visible from the top.

I think the contact point is far enough from the edge that this should not be a problem, but even if it were you should be able to see a noticeable dent in the piston if it hit that hard.

 

[nsxtasy]

Originally posted by sjs:
Perhaps you should read my post again. I'm not a moron, I know all about when a rev limiter will and will not work.

I stated quite clearly (I thought) that I was starting from the assumption that he was correct in his certainty that it was not an accidental downshift.

I misunderstood you and I apologize.

I also know that you have a lot more technical knowledge than I do. By comparison, I'm the moron.

 

[tunapie]

Go with the leak down check. Like the previous msg said, you can isolate the problem and have a good idea what is wrong before you cut the engine open. Dan

 

[sjs]

Originally posted by nsxtasy:
I misunderstood you and I apologize.

I also know that you have a lot more technical knowledge than I do. By comparison, I'm the moron.

It's I who should apologize. I was in a foul mood yesterday, but fortunately I recovered by meeting some local NSXers for dinner. You are certainly not a moron, as anyone who follows this forum would know, and I've learned much from you as well. That's the beauty of these forums, cumulative knowledge and experience. (and the freedom to state the obvious

)

Edit: Just realized that last bit could be misconstrued. I meant that my comments on the value of the forum were obvious, not any of the prior posts.

[This message has been edited by sjs (edited 25 August 2002).]

 

[nsxtasy]

It's all good.

Perhaps we can meet in person at NSXPO 2002?

 

[sjs]

At the moment I'm not planning to attend, but that isn't yet definite. However, I get up your way from time to time so we should be able to meet up and swap stories during one of those trips.

 

[nsxtasy]

Please let me know when you're coming to town. I'd love to get together.