Engine - Rough Idle/Lack of Power/Miss/Backfire

Bulletin No. T 84-82
File In Group 6A
Number 62
Date July '84
SUBJECT: HT4100 CAMSHAFT LIFT SPECIFICATIONS

MODELS AFFECTED: 1982-1985 ELDORADO, SEVILLE, FLEETWOOD, DEVILLE AND BROUGHAM


Some Cadillacs equipped with an HT4100 engine may experience poor engine performance normally described as rough idle, lack of power, engine miss, backfire, valve train noise, or idle surge. This condition may be caused by camshaft wear on one or more lobes.

When camshaft wear is suspected, lobe lift can be measured. A dial indicator should be used at the lifter or top of the push rod while manually rotating the engine. The rocker arm should be removed prior to making the check to prevent inaccuracies in the measurement due to lifter bleed down.

A lobe lift measuring tool (J-8520) is available for use. However, appropriate adapters may be used to allow the check to be made using available dial indicators with sufficient travel.

The HT4100 camshaft lift specifications are:

Intake - 5.840-6.094 mm (.2300 in. - .2400 in.)
Exhaust - 6.031-6.285 mm (.2375 in. - .2475 in.)

A camshaft which measures below these specifications should be replaced with a new camshaft and lifter kit, P/N 1628822.