Fabricating a balance belt guard plate

[aaronth777]

I just finished rebuilding my engine after the balance shaft belt broke, taking out my timing. I didn't have a way to pull the engine block so I decided to install the BSE kit and leave the front shaft in with no belt. I gotta say, I'm not a fan of the vibration. Some say they didn't notice a difference, for me it's significantly worse at idle and over 4000rpm. I'm eventually going to do the work to change the balance shaft bearings and reinstall them, but I had an idea that I don't think anyone has tried before. To avoid taking out the timing if the belt breaks again, could a plate be fabricated to sit between the balance shaft belt and the timing belt? It would obviously be a thin plate, no thicker than the the metal plate on the crank for the crank position sensor. Not sure how it would be shaped or bolted down, I may sketch out some ideas and see what others think. If we could eliminate the risk of catastrophic engine failure then maybe more DSMers will have more peace of mind running the balance shafts. What are everyone's thoughts on this?

 

[Kryndon]

Not feasible. Everything is so tightly packed on the front cover already, that you wouldn't be able to fit a proper shield. A thin plate such as the trigger plate wouldn't hold it. To make matters worse, you've got nowhere to actually bolt it up and install any sort of fastener. Behind the front cover there's solid block. I'm looking at it right now ,and I can't even see if you'd be able to use any of the existing cover bolt holes to mount it up.

Lastly, let's say you somehow got a cover in there and the balance belt snaps once more. You still have the crank rotating at high RPMs presumably, it will keep twisting and mangling the torn belt within the cover. It would either destroy the cover, or severely bind against the tight space and crank gear. You wouldn't be able to react quick enough if this happens at 7-8k RPM.

Also, just looking at the whole configuration, you wouldn't be able to fully cover all the areas of the belt. It would be very flimsy.

You've got two choices: Run the strongest, most proven timing belt (while additionally adding a kevlar/polyurethane layer to it), AND change it often, or just run no belt and no balancer like 99% of us. I'm not saying one is better than the other, but you seem to be worried about this after already suffering catastrophic failure, so these would be your only options.

P.S things like polyurethane engine mounts or a low idle make the vibrations way, way more noticeable. And it's still not nearly as bad.

 

[aaronth777]

Those are all good points and good things to think about. Since the metal would be so thin you're probably right about it not holding the belt if it breaks, it may likely just bend and hit the timing belt. It is definitely tightly packed in that area so i knew it would be a challenge to fit anything else in there. You don't necessarily need to cover the whole belt, there's only a few key areas where it could get lodged in the timing, most notably between the crank sprocket and oil pump sprocket since it turns clockwise.

At some point I'll be getting another engine to build and I can play with the idea a bit more when it's sitting on an engine stand. It's just an idea I had, maybe it'll work and maybe it won't.

 

[pauleyman]

Those are all good points and good things to think about. Since the metal would be so thin you're probably right about it not holding the belt if it breaks, it may likely just bend and hit the timing belt. It is definitely tightly packed in that area so i knew it would be a challenge to fit anything else in there. You don't necessarily need to cover the whole belt, there's only a few key areas where it could get lodged in the timing, most notably between the crank sprocket and oil pump sprocket since it turns clockwise.

At some point I'll be getting another engine to build and I can play with the idea a bit more when it's sitting on an engine stand. It's just an idea I had, maybe it'll work and maybe it won't.

I think youre over thinking this. Change the belts as needed. Ive logged hundreds of thousands of miles on dsms. Ive also changed a bunch of belts

 

[aaronth777]

I think youre over thinking this. Change the belts as needed. Ive logged hundreds of thousands of miles on dsms. Ive also changed a bunch of belts

You're probably right, I'm way over thinking this. It's just frustrating when I changed the belt 4000 miles ago and it breaks somehow. It was a gates belt, but the outer side of the belt sheared off and that's what got caught in the belt. The weird thing is I can still spin the balance shaft by hand so I don't think the bearings seized. Maybe it was install error, i don't know, i was just thinking of this guard plate as a backup option in case something like this happens again

 

[motomattx]

Install a Fluidamper, it smooths it out some.

 

[aaronth777]

Install a Fluidamper, it smooths it out some.

That's a good idea, i hadn't thought of that. Does it help smooth out the vibrations at idle and 4000rpm? I assume the factory harmonic balancer is designed with the balance shafts in mind, but a fluidampr works at all frequencies

 

[pauleyman]

You're probably right, I'm way over thinking this. It's just frustrating when I changed the belt 4000 miles ago and it breaks somehow. It was a gates belt, but the outer side of the belt sheared off and that's what got caught in the belt. The weird thing is I can still spin the balance shaft by hand so I don't think the bearings seized. Maybe it was install error, i don't know, i was just thinking of this guard plate as a backup option in case something like this happens again

What are the details of the install? Who did it?

 

[aaronth777]

What are the details of the install? Who did it?

I did it myself while doing the timing belt change. The balance belt actually broke once before but didn't take out the timing, it was probably just an old belt though as I'm not sure when it was last replaced (the car had around 170,000 miles). So I did all the timing stuff as well as the balance belt and balance tensioner. It ran great, I drove it 4000 miles from north carolina to California with no problems, then it broke a few weeks after getting here. Around 3/4 of the balance belt was still on the sprockets, still tight, but the outer 1/4 of the belt sheared off and that's what got caught in the timing. Still not quite sure what happened honestly. It could have been a bad belt (contitech belt), maybe I over tightened it, or maybe it got caught on the trigger plate somehow. The balance shaft itself felt fine, freely turning by hand, but i couldn't risk another catastrophic failure after just having the head rebuilt

 

[bastarddsm]

Far more likely to loose an engine from a spun rear bs bearing than from a broken front bs belt. At least in my experiences.

 

[spyderdrifter]

I've had engines with no balance shafts paired with poly mounts and while there was some extra vibration, it wasn't bad enough to even be concerned with. As for the belt shield idea, if you still want to tinker with it, do it. What has already been mentioned is valid, deeming this idea somewhat pointless, but it's still not a bad idea. If you can figure out how to mount it, build a multi-piece shield out of 0.020" titanium. It'll offer good strength for being so thin, and add almost no weight (based on it being so thin, and small pieces). I wouldn't say this is an impossible idea to build, and there's plenty who would say don't waste your time, but if you truly think it would help, do it. I had a balance belt break on me too, and the only way I knew about it, was that the engine had crankwalk (confirmed, not imaginary) and I pulled the cover off, just to find the belt was also broken. Didn't really have much more noticeable vibration over my poly mounts. That being said, every engine will act differently. Good luck.

 

[motomattx]

I've had engines with no balance shafts paired with poly mounts and while there was some extra vibration, it wasn't bad enough to even be concerned with. As for the belt shield idea, if you still want to tinker with it, do it. What has already been mentioned is valid, deeming this idea somewhat pointless, but it's still not a bad idea. If you can figure out how to mount it, build a multi-piece shield out of 0.020" titanium. It'll offer good strength for being so thin, and add almost no weight (based on it being so thin, and small pieces). I wouldn't say this is an impossible idea to build, and there's plenty who would say don't waste your time, but if you truly think it would help, do it. I had a balance belt break on me too, and the only way I knew about it, was that the engine had crankwalk (confirmed, not imaginary) and I pulled the cover off, just to find the belt was also broken. Didn't really have much more noticeable vibration over my poly mounts. That being said, every engine will act differently. Good luck.

Crankwalk likely broke/wore the belt from the misalignment.

 

[spyderdrifter]

Crankwalk likely broke/wore the belt from the misalignment.

That's what I had guessed too, but is really irrelevant to this post.