Drill a hole in your engine block??? - ZR-1 Net Registry Forums

Flyman 27 · 09-26-2017

I had the problem with an intermittent no-start condition. After a few days of trouble shooting I figured out that it was the starter itself. So I was well on my way to my first plenum pull and did quite a bit of searching online to see what I could find.

I found a GM Service Bulletin #92-307-6 (09/21/1992) that describes the starter fail and what the GM recommendations are to the Dealers. Obviously they recommend replacing the starter with the corroded Solenoid and say that the problem was caused by insufficient drainage in the "Vee" area of the block (where the starter resides). My drain was plugged solid.

The Bulletin recommends cleaning out the valley drain and also recommends drilling a 3/8" diameter hole in the valley at the rear of the block to add additional/necessary drainage.
It took me awhile to adjust to the idea of drilling a hole in my lt5 engine block, it seemed kinda gutsy.
BUT, I had no luck in cleaning out the OEM drain, no matter what I tried, carb cleaner, brake cleaner, degreaser, etc. Nothing would loosen the clog and it was hard as a rock, I couldn't poke anything through it no matter how I tried. I was able to drill out the clog up to the 90 degree turn, but that was it.

So, I drilled the hole to the dimensions in the SB and it worked great without hitting anything unintended. So the service bulletin was correct and it did work.

If you suffer a starter fail, maybe you should consider the same?

You can do your own search online for "GM Service Bulletin #92-307-6" it is fairly easy to find. So you can verify it yourself.

We Gone · 09-26-2017

I just don't get it wet, I know my 91 has a tube at the rear that exits over the bell housing. I would think a piece of copper wire hooked to a drill would clean it out.

BigIke · 09-26-2017

Great thread! Thanks flyman

Sent from my SM-G950U using ZR-1 Net Registry mobile app

tpr60 · 09-26-2017

Use an old inner speedo cable on a drill to clean out the tube. Every oil change blow compress air up the tube from under the car to keep it cleared out.

Flyman 27 · 09-27-2017

I guess my main point here is that back in '92, GM said that the single 5/16" drain is insufficient for the job. They recommended cleaning out the 5/16" drain AND adding the 3/8" drain hole to help the drainage problem.
Iv'e read a lot about the starter problems here but have not read about adding the drainage hole, even tho it was recommended to Dealers by GM way back in '92.
Just sayin, if you have to do the job, maybe you should follow GM's recommendations on how to fix the known problem.

Dan

RussMcB · 09-27-2017

Quote:

Originally Posted by Flyman 27

I guess my main point here is that back in '92, GM said that the single 5/16" drain is insufficient for the job. They recommended cleaning out the 5/16" drain AND adding the 3/8" drain hole to help the drainage problem.
Iv'e read a lot about the starter problems here but have not read about adding the drainage hole, even tho it was recommended to Dealers by GM way back in '92.
Just sayin, if you have to do the job, maybe you should follow GM's recommendations on how to fix the known problem.

Dan

It sounds like a worthwhile mod, to do while you're in there, even if the original hole is clear. Thanks for sharing (of course, I'll never remember this until right after the next time I put the plenum back on).

Paul Workman · 07-15-2018

NOT to steal the thread, but while you have your drill out, drilling and plugging the rear differential - i.e., adding a drain hole - is also a VERY worthwhile project....Just sayin!

See Marc's(?) web site for specific details.

Hib Halverson · 07-15-2018

Paul is right, while you got your drill out, put a drain plug in your drive axle. When I had my '95, I used Marc's instructions to do that to mine. Made my life a lot easier when it came to axle lube changes, which I did every 3-years.

As for the block drain, my 95's engine had the big drain. Apparently, that was a change GM made after it discovered problems with debris plugging the smaller hole.

jss06c6 · 07-16-2018

Guys,

My top end is out for porting.. just wanted to know, where is the 3/8" hole to be drilled? My drain tube is clear on my '91, but I'm game for improvement!

Sent from my XT1585 using ZR-1 Net Registry mobile app

Flyman 27 · 07-16-2018

I can't post you a link here so,

You can do your own search online for "GM Service Bulletin #92-307-6" it is fairly easy to find. Verify it yourself.

09-26-2017	#1
Flyman 27 Join Date: Apr 2017 Location: Wayne Illinois Posts: 396	Drill a hole in your engine block??? I had the problem with an intermittent no-start condition. After a few days of trouble shooting I figured out that it was the starter itself. So I was well on my way to my first plenum pull and did quite a bit of searching online to see what I could find. I found a GM Service Bulletin #92-307-6 (09/21/1992) that describes the starter fail and what the GM recommendations are to the Dealers. Obviously they recommend replacing the starter with the corroded Solenoid and say that the problem was caused by insufficient drainage in the "Vee" area of the block (where the starter resides). My drain was plugged solid. The Bulletin recommends cleaning out the valley drain and also recommends drilling a 3/8" diameter hole in the valley at the rear of the block to add additional/necessary drainage. It took me awhile to adjust to the idea of drilling a hole in my lt5 engine block, it seemed kinda gutsy. BUT, I had no luck in cleaning out the OEM drain, no matter what I tried, carb cleaner, brake cleaner, degreaser, etc. Nothing would loosen the clog and it was hard as a rock, I couldn't poke anything through it no matter how I tried. I was able to drill out the clog up to the 90 degree turn, but that was it. So, I drilled the hole to the dimensions in the SB and it worked great without hitting anything unintended. So the service bulletin was correct and it did work. If you suffer a starter fail, maybe you should consider the same? You can do your own search online for "GM Service Bulletin #92-307-6" it is fairly easy to find. So you can verify it yourself. __________________ 91-#1935 Black/black & gray, Haibeck 500 Cams by Pete Last edited by Flyman 27; 07-17-2018 at 06:30 AM.

09-26-2017	#2
We Gone Join Date: Apr 2004 Location: ATL. GA. Posts: 2,162	Re: Drill a hole in your engine block??? I just don't get it wet, I know my 91 has a tube at the rear that exits over the bell housing. I would think a piece of copper wire hooked to a drill would clean it out. __________________ Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold

09-26-2017	#3
BigIke Join Date: Aug 2014 Location: Montgomery TX Posts: 263	Re: Drill a hole in your engine block??? Great thread! Thanks flyman Sent from my SM-G950U using ZR-1 Net Registry mobile app __________________ 1991 White ZRJuan #1616 Mileage: 56K Sept-14 -- 113k May-18!!! God Damn I Love This Car!

09-26-2017	#4
tpr60 Join Date: Feb 2011 Location: Salinas, Ca Posts: 159	Re: Drill a hole in your engine block??? Use an old inner speedo cable on a drill to clean out the tube. Every oil change blow compress air up the tube from under the car to keep it cleared out.

09-27-2017	#5
Flyman 27 Join Date: Apr 2017 Location: Wayne Illinois Posts: 396	Re: Drill a hole in your engine block??? I guess my main point here is that back in '92, GM said that the single 5/16" drain is insufficient for the job. They recommended cleaning out the 5/16" drain AND adding the 3/8" drain hole to help the drainage problem. Iv'e read a lot about the starter problems here but have not read about adding the drainage hole, even tho it was recommended to Dealers by GM way back in '92. Just sayin, if you have to do the job, maybe you should follow GM's recommendations on how to fix the known problem. Dan __________________ 91-#1935 Black/black & gray, Haibeck 500 Cams by Pete

07-15-2018	#7
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: Drill a hole in your engine block??? NOT to steal the thread, but while you have your drill out, drilling and plugging the rear differential - i.e., adding a drain hole - is also a VERY worthwhile project....Just sayin! See Marc's(?) web site for specific details. __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry

07-15-2018	#8
Hib Halverson Join Date: Jun 2005 Location: CenCoast California Posts: 899	Re: Drill a hole in your engine block??? Paul is right, while you got your drill out, put a drain plug in your drive axle. When I had my '95, I used Marc's instructions to do that to mine. Made my life a lot easier when it came to axle lube changes, which I did every 3-years. As for the block drain, my 95's engine had the big drain. Apparently, that was a change GM made after it discovered problems with debris plugging the smaller hole. __________________ Hib Halverson Technical Writer former owner 95 VIN 0140 current owner 19 VIN 1878

07-16-2018	#9
jss06c6 Join Date: Aug 2015 Location: Magnolia, Texas Posts: 884	Re: Drill a hole in your engine block??? Guys, My top end is out for porting.. just wanted to know, where is the 3/8" hole to be drilled? My drain tube is clear on my '91, but I'm game for improvement! Sent from my XT1585 using ZR-1 Net Registry mobile app Last edited by jss06c6; 07-17-2018 at 07:23 AM.