The Bullet: Mysteries & Myths
Don't just love but get to know your bullet more

- by B. R. Gurunandan

Noises beyond Cam-gears -

"Silence is Golden"

...if that phrase frustrates rather than soothes, read this one carefully !

So you zeroed the cam-gear backlash, but the euphoria was short-lived. Again the apple of your eyes is sounding like skeletons on a tin roof. What COULD be the problem ? Arrrgh ! There must be a mistake UP THERE, or sins of your past lives coming haunting now, Oooooohh, REALLY you can't recall ANY in this life deserving THIS ! Steady, guys, steady.
There is no Black Magic at work here.
Just the laws of physics and the properties of materials and practicalities of manufacturing processes. Directed by Murphy.
Don't be spooked by the horror stories told by your neighbourhood mechanic or the vintage-collector websites adding half-baked "content" in their ultimate, ulterior motive of metamorphosizing to e-commerce sites.
The remedies are fairly simple and I had not planned to discuss them. But then I got feedback from distressed and confused Bullet-eers, revealing the extent of damage done by the n.m's tales and the v-c. ws.
I repeat : Dikhaave pe MAT jaao; Apni akal lagaao ! :-)

The engine-noise in a Bullet originates from one or more of the following sources. They are classified into three categeories.

Valve-train sources
  Cam-gear Backlash
Power-train sources
  Gudgeon-Pin clearance
  Big-End clearance
  Crank Bearings
  Exhaust-bend seating
  Cyl-clamp on Crank-case
  Tappet/PushRod adjustment
  Muffler elements

Miscellaneous sources of noise
First make sure the noise is not from this categeory ! This is as easy to remedy as to check. Few minutes job each. Only then go on to other possibilities.


One side of the head-steady is fastened to the frame at the tank support, and the other side to a lug on the cyl-head. Make sure both the ends are well tightened. Or you will have buzz-iness in the handlebars, and pinking sound on acceleration.

Exhaust-bend seating:
A BANG on deceleration means an exhaust-leak, and the cause of that may be the improper fitting of the exhaust bend. This sometimes results in an alarming rat-a-tat-tat from the engine-bend junction on acceleration. Dismantle the silencer-bend and re-fit properly.

Cyl-clamp on Crank-case:
This, if loose, also lets the engine vibrate and sound like missing head-steady. Tighten, don't torque ! :-)

Tappet / PushRod adjustment:
This is a VERRRRRY common cause, all because people all too often "adjust tappets" EXACTLY as per "manual" without understanding what they are really doing. We will discuss this at length in "Adjustments" chapter.

Muffler elements loose:
A broken weld or corroded-out internals make the muffler "ring" when the engine is running. Test it by striking the muffler with a piece of rubber-hose or with your finger. If there is anything loose inside, it will emit a metallic ring. Replace if you are sensitive to the noise, but the muffler probably has many years life still in it.

Valve Train Sources of noise
Valve-train noises can be easily differentiated from the power-train noises. PT noises are load-sensitive, whereas the VT ones are not. Theoritically, there are ways to diagnose the noises by simple tests, but conditions and combinations make it quite difficult even for experts to be right everytime. It is best done with a partial dismantle.

Cam-gear Backlash:
We have covered this already in "Cam Gear Backlash" chapter. At the most, the method for removal of original spindles may be a bit doubtful, we may cover it sometime. But some ingenuity would have taken care of that already. (Ya, I do reply e-mail queries)

ValveThe original guides are cast-iron, hard and unforgiving. And are mass produced, meaning doubtful tolerances. Some may be tight, wearing unevenly during run-in, some perfect, some too loose, wearing very fast from the rocking-impact and abrasion. Impact ? Yes. Note how the rockers operate on them. In an arc, not just up and down. The springs hold the valve centered with respect to the valve-seats, and the rockers move the stems laterally untill they are stopped by the guides, when they start a purely axial movement. The stopping is an impact which probably squishes the oil aside, makes oval the guides, which increases the rock & impact & abrasion, and aggravates the problem.
vstemCheck this out for yourself. Remove the cylinder-head, dismantle the valves using the valve-spring-compressor, wash out the guides and stems with kerosene / petrol. Don't look for a micrometer and bore-gauge !!! Don't be taken in by the expansion and tolerance theories. Just rock the valvestems in the guides. Absolutely no lateral movement is allowable.
If you can feel any movement, then it is time to change the guides. The cast-iron ones cost about a third of the bronze ones, and the labour is much less too, but the theory is totally different. Make sure the machinist knows what he is doing, or else you are in for trouble. Ulp ! Now I am in for trouble ! It needs a chapter of it's own to explain the theory of bronze / cast-iron guides, and this one is all about sources of noise. OK, we will take up that one subsequently. Till then take care. BTW, I use Bronze guides.

The tappet-guides also are stressed sideways like the valve-guides. After the cam-nose passes the tappet, there is an abrupt force-direction reversal which tends to cause impact between the tappet and guide, besides the gear-teeth of the cam-gears which we have earlier seen. The temperature conditions are milder than for valves the wear is less. Wash out with petrol & test for rock. The remedy and theory is same as for the valve-guides, but it entails a total dismantle of the engine to change the tappet-guides.

These are very easy to replace, and are available in two types. Cast aluminium blocks and sintered iron blocks. It is not possible to generalise or advise which type is better as there are several manufacturers and the batch variation seems to be considerable too. The best solution is to compare the available ones for fit of rocker-arms in the blocks and shape/finish of the rocker-arms themselves. Again, no play or movement is allowable.
It is highly un-common to bush the rockers, but it is possible and a good engineering exercise. We will go into it one day, so don't throw away the rockers you replace.

Power Train Sources of noise
Apart from being load sensitive, these are the result of long-term wear or serious abuse. So your conscience is a good place to start your investigation of these !

pistonThis is a sharp rat-tat-tat-tat sound on mild acceleration. Comes from long-term wear, or a seizure resulting from over-speeding with a improperly run-in engine.
( Click to read again all about "Running-in" ! Hahaha ! )

pistonfitFirst see if the piston looks anything like in the picture !

Wash out the bore and piston with petrol / kerosene. Insert & try to move the piston side-to-side at various positions in the bore.

If it moves perceptibly, it is HISTORY ! But, not so fast ! Check out bore-wear with a piston-ring. Fit the ring in the bore and push it with the piston till it is perfectly parallel to the end of the bore. This is important. If the ring is not perfectly parallel to top/bottom of bore, you will get WRONG results ! Compare the "end-gap" when the ring is located (a) at the top, (b) at the bottom, and (c) at the middle of the bore. if (c) is much more than (a) or (b), then the bore is worn out. You will also see "ridge" in the bore. A clear case of wear-out. You need a re-bore and change to next oversize of piston.

ring1 ring2 ring3 ring4wrong!
If on the other hand the bore is perfectly parallel, ie, ring end-gap is same at all positions, but still the piston rocks, then you have a once-seized piston. Just changing the piston and rings will be fine. But THIS time run-in the engine PROPERLY ! Put your trust in Science, Logic and Nandan, NOT in Dogma, Mumbo-jumbo and Works-Manuals !

Gudgeon-Pin clearance:

Try to rock the gudgeon-pin vertically in the small-end of the connecting-rod. Actually, this does NOT cause as much noise as we would expect. If there is no problem with the rest of the engine (Bearings and tappet-guides) then it is acceptable to leave this problem pending until the future full-dismantle, at which time the con-rod small-end can be "bushed". But of course, don't tempt fate in the mean while by fitting a high-compression piston or by riding as though you have.

Big-End clearance:

Simple check again ! The con-rod should not rock relative to the flywheels. Test this in half a dozen different positions. This one is serious, though, and the slightest rock means a rebuild. Not a matter of noise, rather about accelerating the wear of a whole lot of parts.

Crank Bearings:
If you can feel movement in the crank-shaft, HEY ! it is HIGH time the engine was rebuilt ! Do not ride hard in this condition, and certainly not for long. Bearing-faults are potential crankcase-distorting problems. That has real expensive repercussions and not always a happy ending.

Hmmmmm. Enough noise about noises :-)

By B. R. Gurunandan

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