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VTEC intake valve huge clearance gap.


gropula

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Hi, all. Bit of background first. Bought bike 2 years ago. Battling high fuel consumption for a long time. Did some stuff like new pressure regulator, cleaned injectors, found and fixed bad grounds etc. All had a small positive effect, but not a real solution. Then I bought rapid bike to tune the bike, help me diagnose and/or circumvent the problem. It kinda did circumvent the problem by reducing injection time up to 50-60% in 5-10-20% columns, fuel consumption improved but it still wasn't great. There was still a weird thing happening sometimes when I add throttle to accelerate and then reduce it to cruise, the bike would then bog down briefly. Next I tried replacing the wiring harness and ECU because I was put off trail by a weird occurrence, injector no.2 intermittently spraying fuel when pump primes. Replaced both ECU and harness, still spraying fuel sometimes. I've accepted that it's not a bug but a feature and moved on. 

 

Today I did the dreaded valve check. Was trying to avoid it at all costs because I wasn't experienced enough in the beginning and having it done in a shop would cost about a quarter to a third of the bikes value. Had to try every other option first. So, here are the results. The problem I'm seeing here is that VTEC valve of cylinder no.3 has a huge clearance gap. 0.50mm, could even fit 0.55mm with a bit more resistance. To me this indicates that the valve isn't seating fully. If that was the case then the cylinder would lose compression, thus reducing vacuum. Reduced vacuum would keep the fuel pressure high at idle and cruise. Also, the ECU would then think that the engine is at higher load, as the MAP sensor is the primary load source at low throttle openings.

Ventili 30.05.2023.png

Didn't do a proper vacuum test, waiting for a gauge to arrive. What I did do is test it at the MAP sensor. 2.89V at atmospheric pressure, about 130m altitude. 2.00V at high idle while warming up, ~1800 RPM. 2.20V at idle when warmed up ~1200 RPM. From the graph in the service manual I estimated that I've got about 160 mmhg of vacuum at idle. Because the pressure drops about 160 mmhg at altitude of 2000m. I'll try to get equipment to do a compression test at least or cylinder leakdown test at best. I ordered a cheap boroscope to inspect the problematic intake valve for carbon build-up.

 

Snimka zaslona 2023-05-30 234558.png

 

 

 

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Good find gropula. Be interesting trying to do a Starter Valve Synch in this situation, probably impossible! The problem would be clear to see on the No.3 cylinder gauge.

MAP graph is purely for static altitude reference, hard to know from that as to actual map reading when engine is running, and the ECM wasn't giving a MAP error.

Are the Valve Springs ok??

Keep us posted.

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Starter valve sync has been done by a mechanic, he didn't say anything was out of the ordinary. Although I visited him because one of the starter valves was broken, so it would have been all over the place either way. I don't remember which one was damaged. I ordered the sync tools as it will need to be done when I handle this problem with the valves. No point in putting it back together just to measure vacuum, as the problem has been found. It just needs to be identified correctly and fixed.

 

Now that you mention springs I remember that I saw that the intake VTEC outer spring at cyl no. 3 no didn't stand upright as the others when I took it out. I just assumed it wasn't standing on a level surface. It was on cardboard so I can label stuff to put it back in the same place. I'll take a pic later and compare it to other springs, but yes it is most probably bent.  Got pictures, they all look the same, just uneven cardboard.

 

The timing was correct when I opened the valve covers, so I don't think there was piston to valve contact. If the valve timing was off the engine would not run right by a big margin. Also other valves would get damaged, not only one, if the piston kissed the valves. Never heard of a dropped valve in a VFR, also the engine wouldn't run for long in that condition. I've ridden this bike for 17k km like this... It could be that the engine was revd to beyond 13k RPM at some point in it's life and only this valve floated and was kissed by the piston... Just a theory at this point, no proof.

 

Every option needs to be investigated now, but as a last resort, the guy that borrowed me the ECU and the wiring harness to investigate the fuel spray can give me the rear cylinder head from the parted out bike. Boy am I lucky to know someone with a parted out '02.

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If you do a compression or leakdown test,  the cylinder you suspect of having a valve not fully closed will quickly reveal itself.  If one or both tests are good, then your valves are likely seating correctly.  You mite check to see if someone has been in there before - look at the thickness of each shim and see if they are similar.  If one is way, way different, then that could be the issue with it being loose, someone screwed up when they did a valve check.  Oddly, when I checked my VTEC valves, all were very tight.  That problem was remedied using a 5th gen motor . . .

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I did a ghetto leakdown test with what I got laying around in the garage. Put some valve cleaning liquid on the intake valves, blasted air trough the sparkplug hole. The valve is leaking, as predicted.

 

Next I tried pushing the valve open manually, with a stick. There is a lot of binding, it's even audible, bigger force required than on the other valve. The valve bucket doesn't bind. It's the valve stem and guide binding. Is there a way to know if the valve is bent or is it some crud making it bind? The big valve clearance gap indicates that it's indeed bent 🙁. To remove the rear cylinder head the engine needs to come out. Then it's easier and cheaper to put another engine in than repair this one.

 

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I assumed previously that a bent valve could be from over-revving the engine. If someone rev'd it to 14k in a bad downshift and only this valve floated it could have gotten hit by the piston. All other valves are fine, which is weird as usually piston-valve contact ends up as catastrophic damage to other valves and sometimes the whole engine. It could be just a small amount of float happened and this particular valve took a small hit. I still haven't received the boroscopic camera, but I doubt that any damage would be visible even if there was piston to valve contact, as it happened more than 17k km ago. Any damage from a small hit would already be covered up by carbon deposits, while big damage wouldn't let the engine run at all.

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I've made a mistake, I've put the VTEC slide pin holder upside down when I pushed the pin in. The valve clearance is in spec. The valve isn't binding anymore, so no worries about it being bent. Although it's still leaking, probably valve seat wear and/or carbon deposits. There's no easy way to fix that so I'll just call it normal wear and tear and move on. I'll adjust the clearances when shims and buckets arrive. By then the vacuum gauges will arrive as well so I'll test out the vacuum of each cylinder and do the starter valve sync. Lots of troubles when I do stuff on my own as I'm not a pro, but I've learned a lot and saved a lot of money doing this service myself.

 

Boroscope revealed nothing fortunately. All looks fine.

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