Thread Repairs

Call us for expert advice and a quotation for your engine machining requirements.

At H T Howard we offer a thread repair service for damaged internal threads.  We have a comprehensive range of sizes available in both metric and imperial sizes.

Primarily we use wire wound inserts but can also offer threaded bush type inserts in certain applications.

Common automotive occurrences for threads needing repair include spark plugs, diesel injector clamp screws, manifold studs, cylinder head bolts and brake calliper mounts.

At H T Howard we only work on components once they are removed from the vehicle.  We do not offer any “in-situ” repairs.

Wire Wound Inserts

Wire wound inserts are precision formed coils of hard wire which can be used to restore stripped, worn or damaged threads to their original size and condition.  If internal threads are damaged for any reason, the strength and reliability of the fixing is reduced.

To repair damaged threads using wire inserts a new tapped hole must be machined to accept the insert.  The old damaged thread is first drilled out using a pre-specified drill size appropriate to the thread being repaired.  The new hole is then tapped, again using a specially sized thread to match the outer form of the replacement insert.  Wire inserts are larger in diameter before installation than the tapped hole. Each wire insert has a tang at its base which is located in the inserting tool and used to drive the insert into the hole.  During installation, the special inserting tool tightens the coil so reducing its diameter enabling the insert to enter the new hole. After installation the coil expands outward against the tapped hole to permanently anchor it in place.  Finally the drive tang is removed and the new thread ready for service.  In many cases the new thread will be stronger than the original.

Threaded Bush Inserts

Threaded bush inserts are a solid thread repair system utilising a repair bush with both an external thread and an internal thread which matches the diameter and pitch of the thread to be repaired.  The bush has a larger diameter formed at its head which locates and seats inside a recess machined as part of the installation process.  This “flange” ensures that the bush will sit flush with the material being repaired.

To effect a repair, the damaged threads are machined out and a new, larger hole drilled and tapped at a size specified by the manufacturer for the repair bush being used.  This new hole is counter-bored using a special tool supplied as part of the installation kit.  This counter-bore houses the flanged part of the insert to be fitted.  A special installation tool is used to drive the repair bush into the newly formed thread down to the point where the flange prevents it going in any deeper.  At this point the installation tool is driven further through the newly fitted bush which “forms” the new thread inside the bush as it passes through.

Call us for expert advice and a quotation for your engine machining requirements.