Low Speed Shuddering/Rough Idle

NinjaFinch

New member
Hi everyone,

I'm beginning to lose my mind over this project, but I'm hoping a fresh set of eyes might help here. I'll try to be as comprehensive as I can.

About a year ago, I bought an '09 DN-01 with a disassembled engine as a winter project. It's now becoming apparent that I've missed something along the line when putting it back together. The bike was originally taken out of service for an intermittent rough idle. And despite what I thought were the actual culprits, I can confirm the previous owner's complaints now that it's running again.

Original Complaint:

-Rough idle (intermittent, worse when warm, disappears at high speed)

-Excessive noise

Original Dealership Diagnosis:

-Stretched connecting rods (?!?)

Problems Found/Addressed During Rebuild:

-Idle Air Control Valve pins 2 and 3 (harness side) backed out of connector

-Water pump felt somewhat stiff when turned by hand (prevailing opinion from multiple shops was that it was still serviceable)

-Damage to exhaust packing ring between rear cylinder header and main pipe

-Spark plug boots arcing to cylinder head

During the first few test runs after reassembly (idle, neutral only, <1 minute), it wasn't exhibiting anything I would call excessive vibration. Same goes for the first powered run to function check the transmission (<3k RPM, cycled through drive/sport/manual, probably 2 minutes or less). For its first day back on the road, it idled and took off fine at first. But after ~5-10 minutes, it began shaking at idle exactly how the previous owner described. Idle speed fluctuates somewhere between 1,250 RPM and 1,500 RPM. Taking off from a standstill worsens the vibrations (felt in bars and seat), but disappears over ~30 km/h. Shaking and noise seems to be tied to temperature, as it will present immediately on a hot start.

There are absolutely no problems at highway speed. No oil pressure/level warnings or coolant temperature warnings are coming on during riding, and engine oil is fresh and correct. Spark plugs, plug boots, timing chains, chain tensioners, and air filter are all new (plug boots are NGK VD01F, per a recommendation elsewhere in this forum). IACV was properly cleaned and reset. No DTCs thrown or stored from either the engine or transmission computers. Engine power doesn't actually seem to be lacking, though I admittedly have no baseline for how a nominally running example should feel at these speeds. I'm personally suspecting it's something to do with how the transmission engages at low speed, though switching between neutral and drive doesn't seem to affect the sound and feel.

Current Suspects:

-Neutral/Drive clutch failing to fully engage/disengage?

-Transmission spool valve dirty/worn (per FSM, unsure of how it actually operates, was definitely not checked during reassembly)

-Faulty N/D solenoid? Tested in proper resistance range (15.6 Ohm @ 18C, nominal 14-17 Ohm at 20C), but haven't tested proper function yet

-Clutch wear? Clutch assembly was removed from engine by original dealership, but was never disassembled

-Internal transmission fault ($7k CAD non-serviceable part, RIP if true)

If I find a solution, the post will be updated.

Thanks in advance!
 

Stretched connecting rods - I'd like to see that!!!!!!!

Excessive noise???? What part of the engine is the noise coming from? Use a mechanic's stethoscope prong to locate it - if it is obvious or in fact, excessive.

I doubt the HFT would be the cause as they have yet to fail from what I've read in recent years (apart from minor issues like a faulty pressure sensor or failed shift control motor), same goes for clutches.

The spark plug boots were a problem for some, but you've replaced them. As you say the bike goes well at highway speeds, but the original owner's complaint isn't fixed despite all you've done to it.

Suggestion: remove the engine oil filter and let it drain for a bit, carefully cut it open by cutting the base plate off using a fine tooth hacksaw about 5-8mm from the base but turning the filter as you go so that you cut only the outer shell. Then with a sharp knife, cut the bleated paper top & bottom and at the join so it can be removed from the core, laid flat and inspected for collected material, noting that some of the debris from the hacksaw will also be evident.
 
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Funny enough, I was waiting on my stethoscope to arrive. And what showed up at my doorstep at 7PM last night?

Yup, I'm going to try pinpointing the noise later tonight. Though at a glance, it seems to be coming from the rear end of the crankcase. I'm planning on a break-in change at 1,000 km, so I want to get all the non-destructive testing out of the way first.

More to follow! Hopefully something substantial.
 

Update 1: In Which We Learn (Almost) Nothing

So this is where the "losing my mind" bit comes in. While playing around with the stethoscope, I noticed that when sitting at a standstill, it happily holds an indicated 1,000 RPM all day. It's slightly loud, and we'll get to that, but there's no RPM fluctuation when it sits warm and in neutral. I should also point out that the stethoscope thus far has yielded me...nothing. This is my first time using one, nothing sounded really out of the ordinary through the scope, just louder.

Anyway, the takeaways from today:

-With any amount of throttle (at least in neutral), the engine sounds exactly like any other Honda I've owned. But letting off the throttle, it'll return to idle, settle for about half a second, then start chugging.
-Valve clearances could do with some revisiting, they seem to be louder than normal.
-Oil pressure warning light isn't coming on...because it's not coming on at all. I did notice that the plate light and instrument backlighting also went out, but I'm too chilly and sore right now to be bothered pulling fuses.
-N/D solenoid had some interesting wear on it. Part of the pattern near the solenoid tip suggests a leak around the first o-ring. A new o-ring was fitted, and something seems to have changed. But the whole scope of problems isn't cured.
-The noise tends to dip slightly for a second when shifting neutral -> drive, then returns.

On my first test ride today, all symptoms came back. shuddering when stopping/idling, rough idle with RPM fluctuations, etc. The only real change was the N/D clutch solenoid o-rings. On the second test ride, the shuddering seems to have at least tamed itself to the point where it's no longer shaking the whole bike when coming to a stop. There's still a noticeable change in engine noise below ~30 km/h, but the vibrations have (hopefully) been solved. So this leads me to believe there's two issues that were overlapping the whole time, one in the clutch actuator circuit and one somewhere in the fuel/air delivery system.

I'll study up on the PGM-FI troubleshooting chart, unless the oil filter autopsy reveals anything new.
 

Do the oil filter thing sooner rather than later I suggest, to rule out/in internal issues.

Regarding the s/scope - did you use the prong to listen here and there on the engine?

Valve clearances could do with some revisiting, they seem to be louder than normal. What's normal??? You say the timing chain tensioners are new. Do you mean new from Honda or 'new' from a donor engine?

Oil pressure warning light isn't coming on...because it's not coming on at all. I did notice that the plate light and instrument backlighting also went out... That need to be rectifed asap. How long has this been the case?

The N/D solenoid and the Lock-up solenoid are not interchangeable, tho they look similar. The wiring adapter on them are different colours for a reason. Perhaps they have been swapped previously??? I'm not sure if the harness plugs are different shape or length to prevent a mix-up, or not, without checking my own bike.
 

Do the oil filter thing sooner rather than later I suggest, to rule out/in internal issues.
Yeah, with the oil light issue coming up, I think I'll park it until I can get to both of those first.

Regarding the s/scope - did you use the prong to listen here and there on the engine?
Yup, poked a bunch of different spots. Fascinating, but maybe I still need to learn to listen.

What's normal??? You say the timing chain tensioners are new. Do you mean new from Honda or 'new' from a donor engine?
Closest setup I have that's comparable as 'normal' to the Dino would be my VT500 Ascot (older, smaller 52-degree twin), which is barely audible if put your ear beside it, but not while moving. My VFR800 and FT500 Ascot are also this way, only my Navi and Goldwing are silent. All chains, tensioners, and other wear items besides the plug boots were sourced brand new from Honda Canada's warehouses.

That need to be rectifed asap. How long has this been the case?
Just today, sometime before the second test ride. The plate light was at least fine before test ride #1. The backlight was noticed during test ride #2, the oil pressure light I noticed while prodding away just before I parked it for the night.

The N/D solenoid and the Lock-up solenoid are not interchangeable, tho they look similar. The wiring adapter on them are different colours for a reason. Perhaps they have been swapped previously??? I'm not sure if the harness plugs are different shape or length to prevent a mix-up, or not, without checking my own bike.
Correct on all counts, and both solenoids are in the right positions with the right plugs. I've triple checked with the FSM and wiring diagrams.

And for reference, here's that patch I was talking about. That little black line underneath the smallest o-ring looks to be the edge of a stain that passes over the o-ring towards the first oil passage/outlet/whatever that's called.

20240604_203142.jpg
 

Yup, poked a bunch of different spots. Fascinating, but maybe I still need to learn to listen. When you find the source of a noise with the s/scope, it is obvious.
 


Update 2: Warmer?

Not a lot of progress the last couple days, and there won't be for some time as I get to other projects. But some electrical prodding and more stethoscope poking has revealed the following:

-EOP and HFT/neutral oil pressure sensors are all functioning as intended
-No actual oil pressure readings due to oil pressure gauge apparently being broken
-Meter/Tail fuse is good, so the problem with the missing indicator should be either damaged wiring or a burnt LED (unlikely, but possible)
-No compression readings due to losing my 10mm adapter -_-
-Rear cylinder head is slightly louder than the front
-Stethoscope is loudest when placed directly on the rear header joint clamp, new gasket might have also been damaged or otherwise bad
-Bottom end sounds okay, at least to me

Based on everything that's going on, I'm suspecting the following:

-Rear injector dirty/partially clogged? Stethoscope indicates that both injectors are at least firing properly.
-Rear valves out of adjustment?
-Exhaust leak? Everything I've read has told me that an exhaust leak near the headers can sound just like valvetrain tick.
-MAP sensor? FSM offers no symptoms based on it.

Sadly, as I mentioned this may not be revisited for a little while as I catch up on other maintenance.
 

EOP and HFT/neutral oil pressure sensors are all functioning as intended. How did you deduce that if the dash display isn't working?

No actual oil pressure readings due to oil pressure gauge apparently being broken. Do you mean the oil light on the dash?

Are both exhaust header pipes hot when idling when the vibrations are apparent? I use a water spray bottle to check temps.

Rear injector dirty/partially clogged? Possible but unlikely. Is the engine actually misfiring - use spay bottle to check.

Rear cylinder head is slightly louder than the front.

There are absolutely no problems at highway speed. No oil pressure/level warnings or coolant temperature warnings are coming on during riding, This is from your first post. What happened since to cause loss of meter/tail issue?

Spark plugs, plug boots, timing chains, chain tensioners, and air filter are all new... Did you fit the timing chain & new tensioners and adjust the valve - or someone else? I thought new tensioners were NLA.
 

How did you deduce that if the dash display isn't working?
Multimeter at the sensors. I didn't get to disassembling the cowl to check the meter end wiring, that's for a later date.

Do you mean the oil light on the dash?
No, one of these:

yd01900-07-thumbnail-1080x1080-70.jpg


Are both exhaust header pipes hot when idling when the vibrations are apparent? I use a water spray bottle to check temps.
There was heat radiating from both headers. I didn't spray them, but it's worth trying.

Possible but unlikely. Is the engine actually misfiring - use spay bottle to check.
I'm still inclined to keep it as a suspect for now. Even if it wasn't the original cause, it spent quite a bit of time sitting disassembled and unprotected before I bought it. I'm thinking it could be dirty enough to ride that line of leaning out but not misfiring. On that same vein, I'm looking to attack the sensors in the PGM-FI system on my next diagnostic session, though I'm skeptical on any of those if it ends up just being a problem in the rear cylinder.

This is from your first post. What happened since to cause loss of meter/tail issue?
Good question. I haven't dug into the cowl wiring yet, but I suspect something got loose or disconnected on that pressure warning circuit. I'm starting to think the plate light bulb may be unrelated, but I didn't get to testing it today.

Did you fit the timing chain & new tensioners and adjust the valve - or someone else? I thought new tensioners were NLA.
I did that myself. I don't know what to tell you other than that the tensioners came in sealed Honda parts bags, from my Honda dealer. But whatever the case, any wear parts that were replaced were all bought new.
 

So the oil pressure gauge you fitted to where thew EOP switch goes is broken? If so, get another and check.
 



When I get back to it, hopefully by mid-next week. It's at the back of the queue until I get some other projects cleared through.
 

I keep thinking of:
dirty or clogged injectors due to old or low quality gasoline.
an airleak between the throttle body and the cilinders.
Throttle valve doesn't close correct (bit worn out)
 



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