Outer Limits 4x4 Board

Replacing camshaft on 4 cylinder daily driver.

All going (reasonably) well until torquing camshaft cap bolts up to their final torque. DS bolt on middle cap won't tighten. Remove bolt & check - looks OK, try another bolt anyway. Nope, still won't tighten.

OK, stay cool. Alloy head, I'll (carefully) Helicoil it.

Yep, have M8 Helicoils. Double check drill size (and maybe this is where I went wrong?) Spec says 8.3mm, I convert that to 21/64, nearest I have is 5/16 (20/64).

Battery drill, grease on tip, drill slowly & carefully. Cuts lightly for a little while, then bites. Time to investigate.

It's already been helicoiled!

Ripped out the old Helicoil, greased the tap, ran the tap down the hole. It seemed to cut lightly all the way down, and it seems snug. I don't see that I have much choice (at this stage) other than to insert another helicoil and see how I go.



Any thoughts?

well if all else fails and if u have enough room, drill and tap the centre of a bolt, say m12, drill and tap farrrrkd thread to m12, apply loctite screw in bolt and cut excess of, clean up start of thread and ur away.

That's a definite possibility. I don't have the skillz to drill & tap the bigger bolt (well, could probably manage if I had a lathe) but I reckon I could tap the head to suit.

A number of the camshaft cap threads have been Helicoiled - I don't remember doing it, but I guess I might've? There's something wrong in the hole - I can run the Helicoil tap in until it bottoms firmly in the hole, but I can't get an M8 bolt in (without using a spanner, and I'm not ready to lean on it that hard just yet.)



Edit: wound the helicoil in until a bolt started to feel tight as it neared the bottom - I figured it was into the taper left by the tap, and wouldn't go much further.

Broke the end off, fished it out with tweezers, then ran a well greased 8mm bottoming tap VERY CAREFULLY down the hole until it wouldn't go any further. Bolt wouldn't quite go in as far as in the neighbouring hole, but the depth was close.

All bolts torqued up OK, so fingers crossed.

There is a better product than helicoil. its a wurth product called a time-sert.

Google for it and read about it...

Otherwise i the head is off and you hae really stuffed it you can it filled wih weld and re tapped.

I am stopped using otrque wrench n bearing caps, use small socket gear (even 1/4 drive) and do it by feel. or by a high quality 1/4 drive torque wrench.

Head studs and anything into steel i would torque so they are evenly tightened.

Also a product called thread repair, I think, have used it and it is a thicker wall than a Helicoil, you can remove the existing helicoil and more surrounding meat, uses standard tap so you need to have enough meat to tap an M10 hole for an M8 repair, Screws and locks in with two tabs that tap in to prevent screwing out. Availiable at bolt/bearing joints.

Joel

a few different people make the solid ones, most bolt shops will sell them, as said above they need a bigger hole than a helicoil - sometimes this is a problem if you don't have enought meat to go that big.

heres a keensert - same sort of thing, screw it in and hammer the tabs down - locks in.

http://www.minibearings.com.au/store/pa ... s/all/1/3/