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914World.com _ 914World Garage _ need to fix a stripped CHT hole

Posted by: brant Jul 10 2011, 11:01 PM

about 3 years back I tore a motor down to rebuild my rebuild.... (long story)
anyways, I only have myself to blame
today I started bolting on the externals and tin

found out that the CHT hole is stripped.

motor is assembled and I really don't want to pull the head at this point for welding......

how do folks feel about a time sert or a heli coil in this application.
I think I happen to have a heli-coil in the right size... but if I had to buy a time-sert to make it conduct the heat into the sensor I would do it.

what do folk think?

John, how would you tackle this repair?

thanks in advance everyone.
brant

Posted by: McMark Jul 10 2011, 11:25 PM

Helicoil would be fine. Brad Anders has found that the CHT heats up too fast in some cases and adds a spacer to keep it cooler longer. But I doubt you would notice a difference in CHT function.

Just don't drill too deep or you'll go into the combustion chamber.

Measure the depth of the OE hole, and put some tape on your drill bit to keep from going too deep.

Posted by: sean_v8_914 Jul 10 2011, 11:31 PM

the hole is shallow. you will need a bottom tap

Posted by: brant Jul 11 2011, 08:12 AM

Thanks Guys!

I think the heli-coil taps are a special pitch and unique to the tool
so its not likely possible to find a bottom tap to match their unique pitch
I'll check out their website and see if they make one.

thanks again
brant

Posted by: r_towle Jul 11 2011, 08:49 AM

buy a tap, grind off the tip until its flat and the full profile of the body of the tap....you have a flat bottom tap now.
Local hardware store tap so you wont feel so bad grinding it down.

I did that one in the car once (never again) and its not to bad.
Timecert worked fine, readings were fine.

Rich

Posted by: brant Jul 11 2011, 09:11 AM

luckily the motor is still on the stand.
I was doing final assembly on the tin work when I discovered it.
I really don't want to pull the heads since I just did the full valve train measurements and cut all of the pushrods.

I just checked and will have to buy that size of heilcoil after all
when I pick it up, I'll play with depth and modifying it.
thanks a ton!

brant

Posted by: Cap'n Krusty Jul 11 2011, 10:10 AM

I just looked on the web, and I don't think Helicoil makes a 10mm x 1 insert. Timesert is gonna be the way to go. I have the kit. PM me and maybe we can work something out.

The Cap'n

Posted by: AvalonFal Jul 11 2011, 04:45 PM

Used a TimeSert to do the same thing. I had to drill out the old broken CHT first. The CHT hole has a bottom so measure and use the tape trick for the drill bit, if drilling, and on the tap. TAKE YOUR TIME and keep the tap perpendicular to the hole. Here's a pic.
Paul
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