Probably depends more on the service history than anything else. ie oil changes (most important). Also any history of severe operating conditions, abuse and the like will affect your decision. If none of the bad stuff applies, take a look at your cylinder walls and piston tops. If no signs of excessive wear, spalling or scoring, the bottom end will probably be OK. BTW, why is the head coming off??

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Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE