rock arm pedestal mount bolt/helicoil stripped

decipha

Registered User
as the title states... bold sentences are the summary for those with little time to spare

i had a helicoil in it that let loose but wouldn't retract, the bolt just spun but wouldn't come out. After fighting with this single bolt for 19 hours straight I came to the conclusion that it wasn't to be removed by normal means. So I tied a wire-coil wound cable (think garage door) around the bolt and tied the other end to the hoist. I then pressed the up button... I completely unloaded the front suspension and then began to lift both the front tires off the ground :eek: keep in mind this is on a single 8mm bolt that holds down the damn rocker arm. Well anyway, I decided that if it was to fly out it would do some uni-body damage by the brute force it would create. So I then lowered the car back on the ground just enough for the front tires to mate the cement. Then I bust out the impact and started spinning her in reverse. After about 15 minutes she finally popped out.

well that was 10 months ago.

I re-tapped her and put a new helicoil in and went putting down the road.
Yesterday i was coming down a bridge when i came to the bottom at a red light i heard a tapping noise. Didn't think much of it because I didn't think it was my car, so i lightly rev'd her up and i tapping get faster. Immediately I thought of the rocker arm and before the light turned green my car started smoking badly and lost power but tapping went away. So i moseyed on down the road to a parking lot and shut her off.

I got the car back home and today after work I yanked the valve covers off.
Well, my suspicion was correct, that was indeed the culprit.

So being the detective that I am I started investigating the matter further to identify the cause. It was pretty obvious with a quick rub of the pedestal mount on the head. The helicoil was not seated completely within the head.
This caused the rocker arm base mount to not seat on the mating surface and by doing so it exerted force upon the rocker arm bolt thus leading to its failure.


luckily i didn't bend a valve nor did i bend the push-rod or damage the rocker or head :cool:

so now im waiting for the special order helicoil to come in.

size of our pedestal mount bolt for rocker arm is metric m8 widthx1.25 pitch

you'll need a helicoil that's m8x1.25x2.0 D (16mm length)

metric helicoil length is measured by a multiplication of the width.
ex: 1.0 D of 8m = 8mm length, 3.0D of 8m = 24mm length
ex: 2.0 D of 6m = 12mm length, 4.0 D of 10m = 40mm length

1mm = .03937 inches

hope this info is useful for someone I'm sure I'm not alone
be sure you use an original 10.9 hardness bolt 8.8 isin't going to cut it
 
I would scrap the heli-coil method and just use a Keen-sert....

These things are as good (if not better) than the original bolt hole.....
 
agreed the heli coil would be good but the other is better. i have seen cat diesel techs use a similar (but I think they are called time-certs to them) on head bolts, the failure rate is very low to not at all and i was even shown pics of a insert that they installed that didnt fail the block failed in other areas. they are some strong mothas.

:D
 
im familiar with time serts but thats overkill for this application


I can understand using an impact to tighten your lug nuts, but you wouldn't
use that same impact to tighten the wheels valve caps would you?
 
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