Multi rib PAS belt turning over / coming off, covered obvious things.

I have a race tuned Nissan RB26 Skyline engine with a problem. The separate multi rib belt that drives the PAS pump form the new and stock crank damper turns over or comes off when the engine is given race type usage. I am 100% sure the pulleys are in alignment in all planes, having even borrowed a Gates laser pulley alignment gizmo. The drive set up is totally stock, the belt is new and genuine Nissan, and the same set up worked on my old engine with no issues. Now, what i am wondering is if the new Tractive sequential gearbox and triple plate clutch are allowing shock loads or rapid RPM changes to get a "wave" in the fairly long belt run, and it then flips over or comes off? I know Toyota run a hydraulic damper on the spring loaded tensioner on the multi rib drive belts on some manual models, but the same set up is un-damped on autos. These belts drive all the ancillaries, mine just drives the PAS pump. My stock Nissan set up doesn't use a pre loaded tensioner, the adjustment is manual and fixed. A similar, separate, but much shorter belt run drives the alternator with no issues. I have made an idler pulley to run on the back of the belt, on the none drive side, to possibly stabilise things, but to test it involves (expensive) track time. What do people reckon my chances of having this effect a cure are? Anyone into drive belt technology, it's frustrating something previously reliable and apparently simple is causing hassle? Thanks

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Try a different brand of belt. It shouldnt make any difference but in my experience it can, Then the biggest thing is slow the pulleys down. I presume it comes off at high RPM and you probably do not need to turn the pump that quick. Bigger pump pulley or smaller crank pulley. A lot of P Steer pumps are adjustable for pressure, a bit less pressure may help.The standard set up is designed for low RPM street use and when you are using 3 times the RPM problems will arise, hence slow the pump down.

After reading post about vibration I noticed mine had a slight amount of vibration at times so I took a look at the belts while it was running and noticed how much they bounced around and I also noticed the large pulley was not running true as I could see wobble while it was turning and figured that could also contribute to vibration so this is what I did to fix the problem and at the same time allow me to add a brake to the lathe.

The belt I chose was a 10 rib 31in poly V belt.

I made a rotor/disc from .120 steel plate and attached it to the smaller motor pulley with 4 bolts. Later I will be adding a disc brake caliper so I can have a brake setup that will allow me to not only stop the lathe quickly but also let me lock the spindle so when I am hand tapping the spindle will not rotate.

The shaft the large pulley bolts to is tapered so I had to remove the original dual V belt pulley and use it to set up the compound so I could turn the proper taper on the new multi rib pulley.

There are a couple videos I posted of the before and after.

<---------Video showing original belts vibrating

<-------- Video showing new belts and pulleys running.



I absolutely love my gg. I looked long and hard and after learning all that I could about lathes in this price range I went with the grizzly. The vibration isn't bad at all. In fact had I not wanted to put a brake on the lathe I wouldn't have even worried about it. But after thinking about how I would do the brake I figured I could also switch to a multi rib belt since they are low vibration belts to start with. The gg is a 12x36 lathe and the G is a 13x40 which to me is the only thing the G has over the gg. The biggest downfall I see in the G is the same problem I saw in the PM which is why I didn't go with the PM and that is having to do a gear change for certain inch threads. If you look at the chart you will see half the inch threads are on one gear set and the other half require another gear set. With the gg you can choose from 4tpi through 112tpi with the same gear set. You only change gears on the gg for metric threading. The feeds work the same way depending on what feeds you want you might need to change gear sets to achieve this. With the GG I can select from . to . feed with the same gear set installed.

These are things you may want to look at before buying.

For me that was a deal killer.