1/8" is a little large. Closer to 1/16" . If we take a look at the thermal expansion rate of Aluminum and pick (22 ×10-6/°C)
https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html
I would estimate that a engine is about 3 feet wide quick calculation shows about .22mm growth for 100Deg C change.
https://goodcalculators.com/thermal-expansion-calculator/
Not all the parts of the engine will heat up the same with heads having the biggest temp change change. So a 100 DEG c change is probably a little low.
john