11-16-2009, 05:59 PM #1
Rotax Racing Retainers and Shims?
A few quick questions.
1) Is it necessary to install the shims?
2) Instead of using the shims under the seal can you put the proper size shims between the springs and retainer to help the springs galling the retainer?
3) How much do the shims add to the spring rate??
4) What is the max shim thickness for stock valves and springs?
11-16-2009, 08:45 PM #2
I have not had my hands on Rotax items yet, but the usual way to lighten them would be to remove weight(metal) from the retainers to reduce reciprocating mass, and static inertial momentum.
Then re-load the valve spring by shimming from the bottom of the spring at the part that doesn't move.
Am unsure as to what the rating would be, but watch the coil angle of the spring doesn't get much below 30 degrees under normal captive point. beyond that, the initial acceleration versus length will be affected, and possibly they will start to expand outwardly beyond their dimensions.
All these things apply stress to the valve as a whole, and typically the weak point is just around the neck of the valve as it flares out to the edge.
Maybe a good idea is to get a bunch of known good quality springs, compress them all to the same captive length, and then take a reading of the pressure they exert upwards. Read the angle of coiling at the same time. Make sure the quality of the metals used is consistent too, and not Chinese quality.
Then start to tinker with shimming, and address this against tensile strength of the valve and its specifications.
Not too hard, and not too soft... this is the problem area. RPM expected against travel of valve with energy in the coiled spring as it accelerates.
I like the quality of the U/G of the RIVA kit I buy here, it is consistent quality. You can buy the shims also(as you know of course), but my guess is more than one will cause problems with them slipping around, so the OEM Rotax ones are a safe bet I feel in one per valve.
The retainer will gall for sure, but much work with an oil stone to a fine polish is a good idea on both top and bottom. Again, the RIVA set-up is well made this way.
11-16-2009, 08:56 PM #3
1) Yes, they work together as a set.
2) No, they won't fit there
As for rate ,and thickness I, don't know, but they work well together with stock springs. I've run mine for a very long time @ 8600 rpms, and only had a 2 break and drop valves. They are supposed to be checked often, and replaced every 50 hrs (so I've heard). I probably have 200+hours on my set, And just broke my second one
11-16-2009, 08:59 PM #4
11-16-2009, 09:19 PM #5
They are now from lots of use...lol I know, I really need to get the titanium ones, but just Can't afford right now....I just wanna ride dammit!!
I dropped an intake valve this time (bent it) and broke 1 guide. I did find an exhaust valve cracked by the head when I dissasembled them. So I got those valves replaced, and changed all guides, and ported the head.
I pick the head tomorrow, and still can't afford to buy the gaskets, and bolts to put it back together yet. I need a 2nd Job I guess
11-16-2009, 09:40 PM #6
Jason, have the spring pressures checked on your stock valve springs
11-16-2009, 11:26 PM #7
11-16-2009, 11:30 PM #8
11-16-2009, 11:33 PM #9
11-17-2009, 09:44 AM #10
- Join Date
- Jun 2005
- rome ga
If I remember correctly the rotax retainers are too soft.
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