'85 500 engine vibration cure?

Thanks for that extra info. I can deal with 'tolerable'.....

Can you get Boyesen Reeds for the '85 any more?

How much power do you think you lost doing this?

Yes there is a lot of good advice... you have all been great. It's much appreciated.

As I am on a budget so the plan is to:-

1. Get the crank balanced
2. Whilst the cases are split get the extra mount welded on.
3. Rebuild bottom end - reassemble
4. Mount back in frame and run engine - check to see if it vibrates it's way down the road
5. Find spare head and have it modified
6. Swap heads and check..

If I get to the point where I think I need more power over the reduced vibration then I can put the old head back on... That's Plan A..

Crank Balance update:

I have just had the big end replaced (even though it was found that the old one was still OK) and the crank balanced. Before he took it apart he checked it and it was out....

Obviously until it's back together I wont know if this has made any difference but it was worth a try....

Stu

Definitely want to hear.

Hi, I would like just add my experience. I had a Bultaco Frontera 370. This one has on the head cylinder two rod connecting to the frame. One day I started to feel a hell of vibrations !. Well one of those rod was broken. After repaired it, the vibrations when low again. I can see also that the old Maico 490 has those rods connecting to the frame. Why not to do the same with the big huskys? I hope it will help, I may try myself also.

The lack of a head attachment point is pretty much a design defect the way I look at it. There don't seem to be locating pins at the cylinder to case connection you really ought to have if you attached it there though and there has got to be a fair amount of stretch in the bolts or studs which hold the top end on. It wouldn't be too hard on the water cooled ones to bolt on a head steady the air cooled ones would be more challenging. I would think one way to deal with the (vibration) issue would to be to sleeve down. You have an 84mm stroke so if you found perhaps an 81 or 82 mm piston and build from there. The less weight on the piston might allow you to fill the crank for volumetric efficiency and get to balance. The water cooled 400 piston is about the right diameter but too short and has a smaller hole for the wristpin.

Fran

I remember that the Bultaco had two special nuts, long body where the rods connect with screw. About the stretch, I believe that in the Maico 490 are attached to the studs ?
I'll see if I find some pictures of the Bultaco exemple.

This discussion has me very interested. I am searching for ways to reduce vibrations on my 1988 WR430 project. The addition of a head stay makes perfect sense to me. I looked closely last night at the design of the head and it appears that a bracket could be fabricated to sandwich between three of the most forward located head bolts (not studs) and mounted to a bracket welded to the front downtube. Three slightly longer head bolts would be required. My question is whether the front downtube would offer the rigidity needed to dampen the vibrations. It appears that Kawasaki's KX250 has a forward mounted head-stay, so it just might work. This is for the water pumper engine, not sure of the head orientation/bolt access on the finned models.

If you really want a two stroke which has minimal vibrations I might suggest investigating the liquid cooled ATK 250/260 which is the only two stroke with a counter balancer that I know of.

I think you ought more think of keeping the rear case intact at the swing arm pivot in adding the head steady. Like I posted earlier the design of the cylinder to case and cylinder to head connection wasn't designed with this in mind. Loss of seal at a base gasket can be quite catastrophic if you don't catch it early. Strangely the four long studs holding on the head are the same for the 430 and 500 the nuts are different but upon mixing and matching air cooled with water cooled the length is different. I think the air cooled ones are longer. If doing this upgrade using the four smaller head to cylinder bolts would be my choice. The proper way probably would be drilling all the way through the frame under the tank and putting in pipe like sections similar to you find where the rear sub frame attaches. You may be right about the downtube being better however my limited experience taking two stroke top ends off from designs currently available the cylinder to case connection is more substantial and the frame mount is not on the downtube.

Upon going to bikebandit.com and pulling up a parts sheet for a 2005 kx250 I see two locating pins at the cylinder to case and a casting on the head pointing to the rear. Maybe it wraps arount the water hose somehow to get to the front downtube.

Fran

I am agree with you about to try to connect to the stud. Even some designs are attached directly on the aluminium head, but as you said, it is designed on that way, and tested by the factorys also.
But there are anothers designs that it would apply I think, as the Maicos, Bultacos, but others brands.
Take a look of this web site with a mix of pictures of vintage head cylinders:
http://www.vta.asso.fr/spip.php?article105

The photos below are of a 2000 KX250 engine showing the forward facing headstay, and a KX250 frame showing the headstay mounting location on the front downtube. It appears that they beefed up this mounting area with some additional steel connecting the front downtube to the rear backbone area. There is probably considerable flex between these two tubes on the Husky WR frame. I may have to do some additional testing and check for the best mounting scenario.

Fran,
I understand what you are saying in terms of the weaker cylinder-to-case mounting arrangement on this 430 engine. I'll have to look more closely at this. In terms of frame bracketry, I was thinking exactly along the lines of welding in a small tube section through the existing frame tube for the mount, just like you had mentioned. I agree this would be the best way.

Abelma,
Great link to that page showing the differing head mounting configurations that are out there.

This is a very interesting topic.

It is clear that the Kawasaki engineers attached to a rigid node, as, I can see in the others brands.
In my opinion, I am not so kind to weld those frames, if it is not necessary. Welding it will change the structure of the CrMo 4130 steel (I believe this is the steel Husky used). Also it will add some deformation and strenght. You have to do it very well.
Why not, as Fran mentioned, design a collar attached closer to the most rigid area ? There on the vertical front tube ?

Sorry, It was not Fran who mentioned the bracket or collar....it was you NYW

Abelma,
It does seem that there are several options for the mounting scenario. I'm not too concerned with welding on the 4130 frame, although I haven't welded on a Husky specific frame before. I've had very good success welding 4130 with a 70ksi filler rod in the past without cracking. The rod trades some strength for good ductility. I think ductility would be more important in this scenario. Although, all welding could be avoided by incorprating a clamp style mount around a frame tube extending from the head bolts. This would also allow complete removal of the experimental headstay if the design proved faulty. Very interesting.

Yep, I think that it will be the option I would take with less risks, and I dont see why it should not work

Hii any updates on this topic?

I've used double/thicker base gaskets on many different types of big bore two strokes and I have never had one lose bottom end from it. Yes, it does raise the port timing, but that is a GOOD thing since the exhaust port has a direct affect on compression pressure, lowering it which is what you want in this case.

To the head stay topic, why weld anything at all? Do it like on a Maico, its just two steel tubes flattened on each end, and bolted at each end to the frame and head. Simple and effective, absolutely no welding necessary. On the base gasket surface, adding a stay to the head is not going to add stress to this area, it is going to reduce it since the stay is going to take a significant load off those cylinder studs which are now doing all the work.

Have any pics with examples of the Maico head stays?

The stays are simple, and you could just as easily make them out of aluminum instead of steel tube. The cylinder end does not mount to one of the head studs, it just mounts through an additional hole with a bolt. I'm sure it would not work identically on a Husky head, but this will give you and idea of the general idea. In all things I believe in "keep it simple" and dont over engineer something just because you can.