Helicoil head bolts... do the holes enter the cylinders?

[brandonv]

This is for a 90' 120 L-Drive....
I got 2 holes for the head than need to be helicoiled. One is an outer hole that empties into the exhaust area, so no issues with cleaning debris or getting shavings into the motor. The other hole is an inner hole and I'm unsure where it empties into. Can anyone advise!?!?

I've already installed the head and a new gasket. If I remove the head will the new gasket still be usable? It does not appear to be a crush type gasket, but I could be wrong.


Thanks!

 

[Frank Acampora]

Re: Helicoil head bolts... do the holes enter the cylinders?

My area is not L-Drives but the powerheads are very similar so: On my Force blocks, none of the head bolt holes enter either the exhaust cavity or the water jacket. If they do, there is nothing you could harm by inserting Heli-coils unless you get ham-handed and drill WAY too deep.

Now, personally, I'm not a big fan of Heli-coils. If it were my block, I would do the following: If the holes are stripped. then just re-tap from 5/16-16 inch to 3/8-18 inch and use the larger bolts in these holes. You will also need to enlarge the holes in the head to clear the 3/8 bolts. Doing this, you need not take off the head--just tap through the new clearance hole in the head--but of course, be careful not to drill past the head gasket because this is where you will be re-tapping and you want all the aluminum there.

Just by way of explanation, if you strip a 5/16 bolt, the hole is by definition 5/16 inch. Standard diameter for hand tapping a 3/8-18 hole is 5/16. 3/8 X18 bolt has 18 threads per inch which means that the threads are less than 1/16 inch high on each side. (because threads are cut in the profile of an equilateral triangle--all sides are equal) So, while you will not get full depth threads in the stripped hole, you will get ABOUT 75% thread depth. This will yeild somewhere around 80-90% thread strength, and the tapped hole will be smaller than the one for the Heli-coils.

When tapping the block, use plenty of cutting oil, or at least a good oil and turn the tap in 1/2 turn at a time then back out and go another 1/2 turn further. Do this until the hole is fully tapped. It takes longer, but you get a better thread and reduce the chance of galling and breaking the tap or dicking up the new threads.

No matter what you decide to do, in all probability you will be able to re-use the head gasket. Because I am tighter than a crab's butt hole --and that's water tight--, on my own engines I regularly re-use head gaskets even though it is recommended to replace them after they have been torqued. ---Of course, when I rebuild for someone else, I always buy a new one so I can say the engine was restored to like new factory condition.

BUY A TORQUE WRENCH and use it--you will rarely strip a bolt. Torque on head bolts is 225 inch pounds. torque in three steps using a spiral pattern from the center bolts to the outer. This keeps you from warping the head.

 

[brandonv]

Re: Helicoil head bolts... do the holes enter the cylinders?

Thanks for input!
I would also prefer to re-tap the holes, but wasn't sure that was a good idea or not since I didn't know where the holes led to. It's also a good idea cause a tap and 2 bolts are cheaper than a $25 helocoil.

So, just to clarify. I need not drill the block prior to inserting the tap. I only need to drill the head up to the gasket and the proceed to rethread it? You dont think the tap won't cause any issues going past the gasket?

I do have a torque wrench and I do use it. The procedure for the 120hp is tighten to 220 in/lbs and then turn an additional 90 degrees. I had a few too many beverages last night and confused 90 deg. for 180 deg. In other words, I got ham fisted with the beers.


thanks again!

 

[Scaaty]

Re: Helicoil head bolts... do the holes enter the cylinders?

Just go easy and slow..grease up (any) the drill and tap..it will catch 90% plus the shavings...lots of in a touch and out, clean off, do it again....you will be fine ...

 

[Frank Acampora]

Re: Helicoil head bolts... do the holes enter the cylinders?

Just be sure that the 3/8 bolts you use are grade 8--six hash marks on the head of the bolt and possibly a circle in the center of the head. Oh yeah--I forgot--the original head bolts may be a little longer than standard sizes. If so, buy the next size up and grind off a little or use an extra washer under it. --unless you have the clearance in the holes so it doesn't bottom out or the unthreaded portion of the shank does not enter the threaded hole.

Standard sized bolts increase in length in 1/4 inch increments. Some Force engines had bolts about 1/8 inch longer than standard.

And I think I transposed the thread numbers--it should be 5/16-18 and 3/8-16. However, the percent of thread cut and the strength of the threads will still be the same.--Actually, the 3/8 thread is slightly stronger and 3/8 bolts take a slightly higher torque value than 5/16. But for your purposes, the same torque on all bolts will be sufficient.