Reducing vibration on 96 Dirt Squirt

[[email protected]]

Hey Guys - message from the UK here.

I've owned my 96 Dirt Squirt for a few years now - one of the only ones in the UK. Ever since I've had it, and despite a full engine rebuild including all new bearings and a re-bore, the bike has had an annoying and quite harsh vibration mid-range, both accelerating and decelerating. I even tried a new crank that Roger Lippiatt kindly sent me but to no avail.

Anyway, I happened to be speaking to a UK two stroke expert last week and he pointed me in the right direction so I thought I'd share with you guys. Can't believe I'm the only one with this problem, which relates to the exhaust mounting.

As most will know, the exhaust is spring mounted into the barrel but solid mounted to the frame at the rear, so any vibration in the exhaust is transmitted straight into the frame where it causes all the extremities to buzz and oscillate. I decided to rubber mount the two rear frame bolts and I also fabricated a head steady (top motor mount you call it), which is solidly mounted. See pics below :

These modifications made a huge improvement and the motor is now really nice to use - still a degree of vibration but it's progressive now - gets worse higher up the rev range, which is what I'd expect.

A couple of notes - I think it's important to mount the springs on the exhaust first, before bolting up the exhaust mounts to the frame. Doesn't say that in my manual but it makes sense to me. Also, the head stead is solidly mounted to the top of the cylinder head nuts via a standard 22mm handlebar clamp attached to the frame tube. In this case it's really important to put zero tension on the mount - everything must bolt up with no tension on the head steady.

Anyway, hope this is helpful. I can't believe that a standard Dirt Squirt was designed to have the level of vibration mine had but it's a lot better with the rubber mounts so 'happy days'.

Tim

[Bill2001]

Good report. Rubber vibration mounts can be had in the US from McMaster-Carr.

I've not noted excessive vibration from my Wombat 94, which has the exhaust pipe solidly mounted to the cylinder with a slip nut and sealing ring. I wonder if there is ( or could be) any advantage to fitting a spring-mounted exhaust pipe to the earlier model?

[[email protected]]

Thanks for your comment Bill.

Another thing I've noticed is that the bike is 'fuelling' much better now, and pulling strongly mid-range, which leads me to think that the vibration was messing with the mixture somehow. Amazing difference.

I'd love to come to the US and try someone else's Dirt Squirt to see if the vibration I was experiencing is 'normal'. I can't find anything else wrong with my bike, such as lose engine mounts or cracked frame, so I assume they're all like mine unless you make some modifications.

[Bullfrog]

I'd suspect that you might have a magneto flywheel which is at the root of the vibration problem you have experienced. Squirts are pretty smooth running in my experience. All of the things you have done seem quite good . . . but most folks don't think about doing them since the Squirt isn't much of a "shaker".
Ed

[Zeek]

Interesting.
Never ridden a Hodaka yet, but getting close to.
Hope it's not that bad.
Anyone have a link to those rubber mounts?

[matt glascock]

Could've the rod or needle bearings been tweeked by someone pushing the wrist pin out with a hammer and drift during a top-end freshening?

[RichardMott]

There is a Hodaka kit that was made for the Wombat. I was going to install it on my CW, but changed my mind.
It is Part Number 948640

[Bullfrog]

I've had the head stay assembly for installation on my Combat engined Wombat since 2007 . . . and it hasn't made it to the top of the priority list yet, so it is still laying on shelf somewhere.
Ed

[michael_perrett]

I have one on my Combat, Rick should have one on his Combat, would have helped at last years Allegheny Forest Ride, since at that time, all his engine mounting bolts were loose. I rode it for all of 200 feet before I demanded my Combat back. Felt like I was the blade on a jigsaw.

[RichardMott]

Well I cannot install it now seeing I gave Mike part of the kit. But he is right. My motor bolts were loose. Bad PM on my part. Shame on me. I was an aircraft mechanic in the army.

[michael_perrett]

To be honest, when I got home from the ANF ride, while cleaning the Combat, I noticed that one of my engine bolts was missing. The other two were tight. Did not vibrate, because of what I believe was the head stay.

Mike Perrett

[RichardMott]

Mike,

How long were you going to keep that little factoid a secret? Ha!

[[email protected]]

Hey Mr Bullfrog
I have the standard flywheel for my 96 Dirt Squirt and I even tried an alternative one to see if it made a difference. I think one was maybe a little better than the other, but neither were good and the vibration persisted. Have you come across an alternative arrangement to the standard engine flywheel? If so I'd be really interested to hear.
Cheers Tim

[taber hodaka]

I think it has been stated before, there were times when we had a vibration and it came from the tank. We draped foam over the frame and then mounted the tank?? Anyway just remembering the past. --------Clarence

[hodakamax]

Vibration? What vibration?

[Bill2001]

That looks a tad abbreviated, Max...

[Zeek]

So where do these head stays attach to the frame? Do they need a bracket welded on?
Also what happens with the head nuts....are they longer than standard.

[matt glascock]

Mine clamps onto the right-side down tube for the frame anchorage with what looks like a handle bar clamp. The two right-side head bolts are replaced with two elongated bolts that allow attachment of the cylinder head anchorage above the fins. These long-headed bolts are threaded at the ends to accept the bolts that attach the bracket to the head. If you go to Strictly Hodaka main page and type 948640 in the search bar, you can see a picture of the whole kit and kaboodle.

[Bullfrog]

The standard head stay assembly for the Model 94 used a pair of handle bar clamp plates to attach to the lower backbone tube under the tank (same tube the ignition coil mounts to).
Ed

[Zeek]

Thanks....i should have just searched for it
Certainly does look like a pair of handlebar holders!
Should be easy enough to make something by the looks.......might wait until i get mine running first and see how it feels.