Shimmed valve clearances. Set during build?
Discussion
A question for the guys with pass car engine assembly experience. Engine that use shims to set valve clearance’s, how do they select the required size shim during assembly?
Do they dry build, measure, strip and then build with the required size? This seems highly unlikely to me. Or do they use a nominal size shim that is designed to land within the middle of the tolerance range?
Thank you.
ETA: title should say build. Bloody phones…
Do they dry build, measure, strip and then build with the required size? This seems highly unlikely to me. Or do they use a nominal size shim that is designed to land within the middle of the tolerance range?
Thank you.
ETA: title should say build. Bloody phones…
Edited by Megaflow on Thursday 27th May 13:14
Boosted LS1 said:
If possible I'd measure the existing clearance and then change the shims to suit what I needed. It's the lobe to follower clearance that's beng measured/shimmed.
Sorry, that’s not what I was asking, I’d like to know how the do the very first build in the factory. 100% brand new components that have never been introduced to each other before. So there is nothing to measure.Yuxi said:
I was lead engineer on an engine assembly line instalation in the Philippenes,I was responsible procurement, technical sign off and instalation of a machine to do exactly this.
It was a 4 cylinder petrol engine, 16 valve DOHC engine. Cycle time was 3.85 minutes.
Heres the process -
Engine with head already on (with cam caps attached, these have not yet been removed after machining the cam bores) arrives in station, in parallel the pair of cams for the that engine are put into a gauging machine which measures each journal diameter and each lobes base circle diameter and distance to journal center. The engine goes into a machine that measures cam bore diameter and valve tip to cam bore center.
With this information the machine control works out the ideal tappet thickness for each valve.
An operator takes a fixture with 16 holes in it and places it on a slide in front of the tappet storage rack. Lights on the rack then guide the operator to select the correct tappet for each valve and place it in the fixture.
Once the fixture is full its then taken to another machine which measures the thickness of each tappet to ensure the correct tappet has been selected.
Next the cam caps are removed then the fixture with the tappets is placed on top of the head locating in two reamed holes. The tappets are then pushed through the fixture and into the tappet bores.
Next the two cams are fitted, then the caps are fitted using 20 electric spindles.
Then each position is checked manualy by an electronic gauge which works by measuring the distance between two balls which locate on the face of the tappet and the base circle of the cam.
Any out of limit are replaced manualy.
Its not an exact science and there is always a "fudge factor" built in to get the correct result.
The machine cost 1.3 million Euros 15 years ago.
I also did the conrod weight grading, piston, and main and big end bearing liner selection equipment.
Beautiful. Exactly the information I was looking for, thank you Yuxi.It was a 4 cylinder petrol engine, 16 valve DOHC engine. Cycle time was 3.85 minutes.
Heres the process -
Engine with head already on (with cam caps attached, these have not yet been removed after machining the cam bores) arrives in station, in parallel the pair of cams for the that engine are put into a gauging machine which measures each journal diameter and each lobes base circle diameter and distance to journal center. The engine goes into a machine that measures cam bore diameter and valve tip to cam bore center.
With this information the machine control works out the ideal tappet thickness for each valve.
An operator takes a fixture with 16 holes in it and places it on a slide in front of the tappet storage rack. Lights on the rack then guide the operator to select the correct tappet for each valve and place it in the fixture.
Once the fixture is full its then taken to another machine which measures the thickness of each tappet to ensure the correct tappet has been selected.
Next the cam caps are removed then the fixture with the tappets is placed on top of the head locating in two reamed holes. The tappets are then pushed through the fixture and into the tappet bores.
Next the two cams are fitted, then the caps are fitted using 20 electric spindles.
Then each position is checked manualy by an electronic gauge which works by measuring the distance between two balls which locate on the face of the tappet and the base circle of the cam.
Any out of limit are replaced manualy.
Its not an exact science and there is always a "fudge factor" built in to get the correct result.
The machine cost 1.3 million Euros 15 years ago.
I also did the conrod weight grading, piston, and main and big end bearing liner selection equipment.
Edited by Yuxi on Monday 31st May 08:03
colin_p said:
I would have thought in this day and age most (non racing or specialist) engines would have hydraulic tappets which negate the need for shimming.
I'd be interested to know what doesn't and i'd also be interested to know if pushrod ohv engines are still being made? I'm fairly certain some Amercian V8's still are?
Lots of industrial off highway diesels are still OHV & pushrod.I'd be interested to know what doesn't and i'd also be interested to know if pushrod ohv engines are still being made? I'm fairly certain some Amercian V8's still are?
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