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#1
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380SL Valve Adjustment Theory...
I'd appreciate some feedback on this.
380SL, 116.962 Replaced cams, rockers, HLAs. I don't have the special gauge tool for the purpose of selecting the correct shims - (I probably need some shims anyway because apparently the preload was increased in late 82 after my car was built). But I need to get the job done. Now here goes. My understanding is that the HLAs have a range of movement and that this movement ensures that oil pressure keeps the rocker pushed against the cam with zero clearance for 360 degrees of the cam's rotation. Now the HLAs have preload i.e. some of the movement is taken up when static, presumably primarily to make sure that there never is a rocker/cam clearance due to the HLA reaching full extension on it's own internal stop and hence not pushing against the rocker, even after a small amount of wear. At this moment in time I don't know why too much preload (within reason) could be a problem, whereas I can see how too little (a gap) could cause cam slap and wear. But that's an aside. I made up a "tool" that is basically a depth gauge when used in conjunction with a vernier calliper. Sort of like the Benz tool, but without the actual sliding plunger, just a hole for the vernier's depth measuring rod. But my problem now is that I don't have a reference marking, as the Benz tool has. My cams were worn, so too rockers, and some HLA ball sockets so no old readings worth anything. I am thinking: Take a reading without the rocker in place, with an HLA fully extended. Fit rocker, take another reading, hence effectively measuring preload and compare to the preload figures in the engine manual. (1.2 - 2.4mm) Will this work? Apologies if something is not too clear I will elaborate as necessary. And thanks in advance. |
#2
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The process that you have outlined is the equivalent of using the revised gauge # 117 589 06 23 00.
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#3
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Thanks Frank, so basically I understood it right, the preload that is referred to is the amount of compression of the HLA compared to fully extended.
If this is the case then it's not too difficult to figure out where we are at and what is needed. If perhaps a little bit expensive when it comes to buying the shims! Is it just me, or has anyone else noticed how 107 parts prices have shot up in recent years. I am resto'ing my '82, I bought most of the bits around 10 years ago but did not complete the job, now picked up where I left off and I just don't remember any major parts prices pain back then. Thankfully I'm only needing the final 10% or less of bits. Must be quite shocking to have to start from scratch today. |
#4
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For hydraulic lash adjusters in general across the world of engines and baring a specific measurement, 1/2 compression is about right, this gives you room to take up for wear of the cam ( adj extension ) and compression to account for valve face wear ( adj compression ) .
The preload was probably increased late 82 to take care of a cold start valve tap. You've got the theory down right. The lash adj will need time to bleed down so make sure you are not forcing the valve to be open. I've put various motors together that would run rough until the lifters bled down so the valve were not held open Past that, this isn't something that you have to fight 0.001 " I'd measure full compression of the adj, pop the parts together with the cam at the low spot before the adj expands, then measure how far it extended. |
#5
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Thanks 97SL, very reassuring and helpful, Ron
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