If it doesn this continually it could be the oil pump pickup is loose or an oil filter as well. There are a few other things it could be as well but the motor would have to come out to check them. Also check the pin on the bottom of the distributor. One other thing if this crate motor has a roller cam an dyou don't have the correct distributor gear the gear on teh distributor will wear very qyick. Check with amanual pressure guage to make sure it is doing what you say as it may be just he guage or sending unit that is not working correctly.