[Vascar]

Is there a set temperature to measure parts for an accurate reading? Can the block measurements be accurate if they are not at the right temperature? I seen a set of mains move .001 with a temerature change. Then I wondered if the machining process should be done in a controlled environment? Does anyone check the temerature of all the parts before machining to get the most accurate readings, or maybee I'm just a nut, you tell me.

[Vascar]

Is there a set temperature to measure parts for an accurate reading? Can the block measurements be accurate if they are not at the right temperature? I seen a set of mains move .001 with a temerature change. Then I wondered if the machining process should be done in a controlled environment? Does anyone check the temerature of all the parts before machining to get the most accurate readings, or maybee I'm just a nut, you tell me.

[Todd]

[This message has been edited by Todd (edited 07-18-2000).]

[Roar]

Measure all the # when it have been sitting in room temperature for awhile and you will be safe.

[Real Pontiac Owner]

Just about every blueprint I have ever seen with a fit temperature specification says checking the fit and dimensions should be done between 68/F and 70/f, and some even specify checking at a certain humidity, too.

[Vascar]

Some shops like mine the guy trys to conserve enery so turns down his thermostat. When he gets in he turns the heat back up but the parts are cold now. I think I should have sent him some blankets. Hahahaha. I just wonder wher the engine specs wind up after they reach the 70 degree mark.

[Nathan]

Here's an example of the effect of temperatures on assembly clearances.

In 1984 I bought a 1973 Opel Manta 1900 from a co-worker. He had the engine rebuilt 10,000 miles earlier and had hopped the engine up quite a bit. At 10,000 miles he scuffed a piston/bore. He sold the car to me.

I tore the engine down and found that all the pistons, at the gauging point, were 0.0005" bigger than the bore!!! I couldn't believe that the engine would even go together like that.

I took the block to a reputable shop to be honed out to the proper diameter (about 0.002" larger than it's current size). They quoted me a price of $30. When I went to pick it up, the price was $65.00. They explained that the casting was so hard that they had to hone for a short time, then wait for it to cool because the block was getting too hot. The honing job took more than twice the expected time.

I then realized why the engine had been built so tight. The guy who machined it, who I also knew from work, had built this engine as a favor to the owner, but didn't really want to do it. As a result, he rushed through the boring/honing operation and took all of his bore measurements while the block was still hot. The piston skirts flexed enough to allow assembly, but were way too tight.

I reassembled the engine with the factory spec clearances and drove it for more than 20,000 miles before selling the car. I had no engine problems.

Ideally, all parts should be at a constant "room" temperature for 24 hours before measurement and assembly (diesel fuel injection pump manufacturers observe this protocol at 70 F before matching parts that have running clearances of 50 millionths of an inch). However, this is probably overkill for an engine. 6-12 hours is probably enough if none of the parts has been subjected to unusually warm or cool temperatures.

Nathan