Buick Roadmaster Engine >> MAIN BEARING KNOCK

Buick Roadmaster Engine >> MAIN BEARING KNOCK

Main Bearing Knock On
GM 3.3 & 3.8L (Buick 3300 & 3800) Engines

AERA members report knocking noises coming from the front of GM 3300 & 3800 Buick engines. The noise is most noticeable when the engine has reached operating temperature. One possible cause for this knocking noise may be from excessive oil clearance at the front main bearing location.

Diagnosing excessive main bearing clearance is easily done by removing the accessory drive belt from the engine after it has reached operating temperature. If the noise diminishes when the engine is started again, front main bearing clearance may be more than .0012 (.030mm). The clearance may be reduced by installing .001 (.025 mm) undersize main bearings. GM permits the use of only one bearing shell half in the cap, but warns not to reduce
clearance below .0008 (.020 mm).

GM specifies the main bearing clearance as .0008-.0022 (.020- .055 mm). AERA suggests machining the crankshaft main bearing journals and the main bearing housing bore so that the minimum allowable clearance is maintained, avoiding the possibility of main bearing knock.

The AERA Technical Committee

---

Looking for replacement Buick Roadmaster engines? Visit our online Rebuilt Engines Store. Need to fix your Buick Roadmaster engine? Access here the comprehensive online repair guide for your Buick Roadmaster engine. Click Here to find a used Buick Roadmaster engine.