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Valve rattle question


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I hope this isn't a dumb question.

I took my newly purchased 1975 Tii clone in to see the mechanic. A dozen or so years ago (at 125k miles), the engine was rebuilt and a Kugelfisher FI and a '72 Tii intake manifold installed to simulate a Tii. A Schrick 292 cam was also installed and the compression raised... I believe to 10 to 1. I don't know if new valve springs were installed along with the cam.

The OD now has 163,000 miles on it. I brought the car in to have the compression and oil pressure taken and to diagnose the general condition of the car. The idle was waffling, it was hard to start and there was valve clatter.

During service, my factory trained BMW mechanic (now an independent) adjusted the valves to factory specs. He fixed a few vacuum leaks, replaced the cold start valve, two leaky injectors, cleaned the fuel pump, adjusted the distributor, and put in hotter spark plugs. The engine now starts easily, runs smoothly and idles steadily.

However, the valves still clatter, especially under mild acceleration. My mechanic said to bring it back and he could reduce the clatter by tightening things down, BUT at the risk of doing some possible damage. I believe he said it could burn the rocker arms or rocker axle? Maybe I got that wrong?

To fix the problem correctly may require a valve job and installation of springs appropriate to the more aggressive 292 camshaft.

Not being an expert on engines and modifications, I kind of understand this, but was hoping there was an FAQ I could read to educate myself.

Is there a way to reduce the valve clatter with a 292 cam installed, or will it require new springs to match the hotter cam?

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Your mechanic probably meant that he could tighten the valve clearances a bit tighter than factor spec. That could reduce the noise slightly but the risk is to burn a valve if it doesn't close totally in some circumstance.

The clatter is not due to springs but worn cam and/or rockers and/or timing gear. 292 cam is fine with std valve springs if you don't rev it much higher that stock rpm limit. To get rid of the clatter you need basic head overhaul job and replacing worn parts.

Tommy

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Could also be a worn timing chain. My old engine had a LOUD rattle...my mechanic diagnosed it as a bad timing chain. Since it was a stock engine, with low compression and needed a valve job, timing chain, and rings..no te mention carb work I opted to replace the whole unit with a rebuilt high performance engine....so if you chain is stretched..it'll rattle.

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