HT Engine Noise Reduction

Discussion in '2-Stroke Engines' started by AussieSteve, Dec 11, 2009.

  1. AussieSteve

    AussieSteve Active Member

    When I start my engine, I stop for a minute to warm it up a bit before riding. I usually put my hand on the side of the barrel/head to feel when it's beginning to warm up.
    I've noticed hat the clacky 2-stroke piston slap noise is drastically reduced while my hand is on it. (Try it)
    A lot of my dirt bikes had small rubber blocks between the fins to reduce noise. It would probably help a lot with these engines. The fins are extra-thin and ring easily.
    The drawback is that cooling efficiency will be reduced a little.
    I'm going to try it tomorrow and see if it makes much difference. It won't work as well as my hand, but...

    ... Steve.
    Last edited: Dec 11, 2009

  2. Al.Fisherman

    Al.Fisherman Active Member

    Actually Steve, if the blocks are placed right, much like your dirt bikes were, they won't have or should not have any effect on cooling, if so I'd guess very little. Look at the torture a dirt bike goes through as compared to a HT.
  3. AussieSteve

    AussieSteve Active Member

    Yep, my thoughts exactly, Al. I only really mentioned that cooling efficiency would be reduced to remind others not to overdo it.
    I used to ride a Bultaco Sherpa T 360 in trials competitions years ago. It had more rubber than any other bike I've ever owned, yet was intended to run at very low speeds with very little air flow. Heat was never a problem there.

    Since posting, Ive done a bit more reading. The other biggie for noise reduction is to attach a piece of corrugated cardboard to the inside of the clutch cover. For even better noise reduction, glue an old mouse mat, cut to shape, onto the outside of the clutch cover. Sounds messy, I won't be doing this one, but the cardboard apparently reduces clutch noise heaps, so I'll definitely do that tomorrow.

    ... Steve
  4. Al.Fisherman

    Al.Fisherman Active Member

    There is an aftermarket clutch cover offered. It is made of plastic. I'm not concerned about noise here. Heck Harley's make more noise idling then a HT at full bore.
  5. AussieSteve

    AussieSteve Active Member

    I hate the piston slap sound so I want to quieten that as much as possible.
    The only time the clutch noise bothers me is when free-wheeling down hills with the clutch disengaged - I'd like to quieten that a bit.
    ... Steve
  6. I use small pieces of rubber hose inbetween all my fins top and sides(gets rid of the ringing noises).I put 3 gaskets for my clutch cover so the clutch doesnt scrape the cover. I used thin rubber taped under my engine mounts(all vibration gone until 30mph).
    Im using a muffler strap connected to frame. Cruiser tires provide a smooth ride.
    I made a snorkel for my aircleaner(gets rid of intake noise). I have a black cat muffler so its already quiet. Next i will try and quiet the clutch cover.
  7. Pablo

    Pablo Motored Bikes Sponsor

    Most of the noise from mine is the noise of the combustion explosion emanating from the cc and going up and out. I tried silicone blocks....didn't help much....if the head was thicker, it would be quieter.

    How do those turned custom round heads sound? I gotta get me one of them.
  8. AussieSteve

    AussieSteve Active Member

    Hi Pablo, it sounds like you have less piston-slap than mine. I could hardly hear my exhaust before.

    I don't tend to exaggerate and this is no exception.
    I did both mods, very thin corrugated cardboard inside the clutch cover, adhered with RTV silicon, then I put extra beads of silicon over the top, to stop the cardboard resonating.
    I have a length of 1/8" rubber strip here, so I cut (roughly) 20mm x 8mm pieces, then folded each in half and jammed it between the fins, aiming for the points where the fins protruded furthest.
    The difference has to be heard to be believed. The best, cheapest, quickest mod I've done so far.
    I had a problem with clearance of the 3 clutch locator pins, so I cut a washer shape out of the cardboard to allow clearance. Two cuts with a sharp blade and it peeled right out.
    (The cardboard I used was extra-thin corrugated cardboard, as used for digital tuner boxes, DVD recorder boxes, etc.)

    On my (10 mile) test ride, all I could hear was the exhaust.
    Now that it's tuned about right, that sounds good. Piston slap doesn't.

    I'm still on the stock head for now, Pablo, until the longer studs arrive.
    (Thanks for going out of your way on that one.)

    Still, even using the stock head, after going 0.06mm leaner on the main jet and dropping the slide needle to it's lowest, (leanest), setting, along with 4 x 4mm holes on the inside of the stinger/tail-pipe, my top speed has gone up to exactly 50.0 kph, (31.3mph). (44T sprocket, 26" wheel, flat ground, no tail-wind, accurately calibrated speedo.)

    Just did my math with the help of 'GearRatio.exe', at 50.0kph, the engine was doing 7280RPM or very slightly less. That's going pretty hard for one of these things.
    I don't want to go faster than that but more power will be great.
    I'm dying to get the hi-comp head back on. The difference is worth the money. A shame about the stud hassle, but life wasn't meant to be too easy.
    A couple of guys are waiting for me to post results on compression, too. My stock head weighs in at 115psi. I still need to re-test the RSE billet head, I think it was leaking when I prevously tested it at 135psi due to the stripped cylinder stud nut.

    ... Steve
  9. AussieSteve

    AussieSteve Active Member

    Pics of both mods

    Al, totally by coincidence, a couple of Harleys pulled up out the front so the riders could have a chat, (yell), to each other, earlier. The Harleys sound nice, but definitely not quiet. I want my HT to be quiet, to avoid offence/cops/etc.

    As I worked earlier, I took a couple of pics so I could show them if I was successful.
    Here they are. The pic of the inside of the clutch cover was before I added the extra beads of silicon for deadening. A medium bead every 1/2" seems to work well. (Cross-hatched.)
    The corrugated carboard was about 1/16" thick.

    * Forgot to say earlier. To work out where to cut the 'washer' shape out of the cardboard, first stick it on and let it set, then screw on the side-cover firmly and roll the bike forward a little, (clutch disengaged is OK).
    Take the cover back off and cut either side of where the locator lugs have left their mark, then peel out the waste.

    This does work, believe me:-


    ... Steve

    Attached Files:

    Last edited: Dec 12, 2009
  10. AussieJester

    AussieJester Member

    If the rubber doesn't work out, something i would suggest is getting a length of
    threaded steel rod, 4-6mm thickness would do it, and a handfull of nuts/loctite. Bore holes vertically down through the cylinder head fins, slide the threaded rod down as it passes through each fin add two nuts, once you have the rod passed all the eay through with two nuts between each fin, nip them up tight to press firmly against the fin. I think if you did for of these around the head it would do what your after...my2c


    p.s the reason it does 'work' is because it stopping the fin vibration, vibration = noise stop the vibration you will stop noise :)


    here's a quick photochop better explaining the idea-->


    The use of steel rod would actually improve cooling as your adding additional 'heatsink' properties in the form of the threaded rod to the head ;-)
    Last edited: Dec 12, 2009
  11. AussieSteve

    AussieSteve Active Member

    No need for that - it's all good. The difference really has to be heard to be believed.
    Regarding your method, Kim, an old variation on that is to drill a 1/4" hole vertically down through the fins, then thread 1/4" rubber tubing through the holes and finish with a length of 1/8" wire through the centre, bent over at both ends. Works really well. (On dirt-bikes, at least.)
    Still, as I said, the rubber blocks are grouse. If some fall out occasionally, I've got enough rubber for hundreds more.

    <edit>and the clutch noise when freewheeling with the clutch in is seriously reduced with the cardboard.</edit>

    ... Steve
    Last edited: Dec 12, 2009
  12. Pablo

    Pablo Motored Bikes Sponsor

    Interesting ideas....some of Jim's engines clutches/gears have been loud, mine are relatively quiet. I have no noticeable piston slap.....just loud (natural) head explosion noise!
  13. give me vtec

    give me vtec Active Member

    I have done this... except I used some old foam rubber I found in the road. It worked great...
  14. AussieSteve

    AussieSteve Active Member

    Pablo, bad machining tolerances or something, I guess. The day I first started mine, it sounded like it had a broken piston skirt. That never changed, but I got used to the sound and realised that it was normal?.
    I considered buying one of Tony, (RSE)'s ceramic coated pistons.
    Now, after todays little mods, like you, all I hear is exhaust, as it should be.
    On the clutch side of things, I read today that some engines have helical-cut primary gears, whereas others have square-cut. The square-cut apparently make much more noise. Mine are helical. Glad I don't have square-cut.

    If things are noisy, the rubber blocks and cardboard are well worth the effort, (and cost, ~ $0).

    .... Steve
    Last edited: Dec 12, 2009
  15. AussieSteve

    AussieSteve Active Member

    Yep, as I said earlier - cost $0 for old rubber and cardboard, but the difference...
    It's not BS like some speed claims etc.

    ... Steve
  16. flashstar

    flashstar Member

    I also get some rattles that seem to be coming from the clutch. Rattles from freewheeling don't seem to be too bad, although it does make it sound like I am riding a really crappy bike! :dunce: I'll give the cardboard a shot.

    When motoring and especially engine breaking at higher speeds I do get a higher-pitched rattle which is fairly loud and comes and goes while changing the amount of throttle that I give the engine. This is somewhat worrying but the engine provides good power regardless of the rattle so I guess that it's normal. When I talked to Duane he mentioned that this is fairly normal.

    I'll make sure to give the fin padding and clutch cardboard a shot. Thanks for the ideas.
  17. AussieSteve

    AussieSteve Active Member

    Pablo, if you're still watching this thread, I just noticed that one of my pics on the previous page shows my stud lengths clearly. Level with the tops of the nuts w/ a stock head and 1 head gasket.
    You can picture how it would look with the 3mm thicker billet head. Only half of the nut bites.
    ... Steve
  18. Pablo

    Pablo Motored Bikes Sponsor

    I saw that. Crud, I forgot to bug Jim about the longer ones.
  19. AussieSteve

    AussieSteve Active Member

    I'm in no rush, he did say that it would be a week or two and that he'd get back to me.
    I wasn't trying to rush you.
    I'll get a couple of other things too. I love the slim-line air cleaner. It's high on the list.

    ... Steve
  20. Pablo

    Pablo Motored Bikes Sponsor

    Thanks.....we've been a tad crazy lately.