Hydraulic lash adjusters
What decides a lash adjuster
Six characteristics carry the part. Each comes with the reason it matters and the instrument that proves it, because a characteristic that cannot be measured cannot be held.
Six characteristics
And the instrument behind each one
- Plunger to bore fit
- A few microns of diametral clearance, set by the leak-down rate the engine needs. It is held by honing the bore, superfinishing the plunger, and matching the two by class rather than relying on a tolerance stack. Proved by: air gauging of every bore and every plunger.
- Leak-down rate
- The time for the plunger to move a fixed distance under a fixed load, in test oil at a controlled temperature. The specification is set by the engine, and it is the one number that summarises the fit, the finish and the check valve together. Proved by: a leak-down rig, on every part.
- Surface finish
- Sub-micron roughness on the plunger outside diameter and the bore. A rougher surface leaks unpredictably and wears the fit open. The roughness tester carries the full parameter set, because a sealing surface can pass on Ra and fail on Rz. Proved by: surface roughness tester.
- Hardness and case
- Working surfaces case hardened so they resist wear at the fit and at the pivot head, with a tough core underneath so the part does not crack under a valve spring for two hundred million cycles. Proved by: hardness testing on site, closing out the heat treatment.
- Check valve seat
- A ball has to seal against a seat in the plunger floor every revolution. The seat geometry, its finish and its concentricity to the bore decide whether the chamber holds pressure or bleeds. Proved by: contour tester for the seat profile; leak-down for the result.
- Cleanliness
- A particle on the seat holds the ball off it, and the adjuster collapses. Parts are washed to a cleanliness specification and assembled in a clean cell. Proved by: particle counting against the specification, ISO 16232 or VDA 19 as the drawing calls.
Why the fit cannot be a sample
Every adjuster is its own fit
On most turned parts a capable process and a sampling plan are enough. A lash adjuster is different, because the characteristic that decides it is a relationship between two parts rather than a dimension on one. A plunger that is in tolerance and a bore that is in tolerance can still be the wrong pair.
So each is gauged, sorted into a class, and married to its partner from the matching class. The result is a fit held to a fraction of the individual tolerances, and it is confirmed by the leak-down test on the assembled part rather than inferred from the parts. That is also why the test is on every adjuster and not on a sample.
A leak-down specification on the drawing is quoted against directly. Where the drawing carries a fit and a finish but no rate, the rate the engine needs is agreed before quotation, which costs less than settling it at first article.
Send the drawing
A clear answer inside a working day
A 2D or 3D file, the quantity and the date you need it. You will get a considered reply within one working day, including the reply that we are not the right shop for the part, which is worth knowing early. A mutual NDA is issued first on request.