So what did you do to your GMC today?

[LarryW]

Sailor, you might want to check the 5 and 7 plug wires, they should have a fair bit of separation but in the photo they look like they're very close or even touching in a couple of places.

View attachment 18543

Pretty engine!

Richard RV is right. 18436572 is firing order. 5&7 are adjacent in firing order and when close parallel install may get some induction from one wire to the other making it feel like a minor miss. Just say'n.

 

[Wally]

Richard RV is right. 18436572 is firing order. 5&7 are adjacent in firing order and when close parallel install may get some induction from one wire to the other making it feel like a minor miss. Just say'n.

Jasper engines has a tsb on 5-7 ignition crossfire. Attached file

 

[Richard RV]

Jasper engines has a tsb on 5-7 ignition crossfire. Attached file

Good find, Wally. Absolutely should be posted in Resources.

 

[sailor man]

Sailor, you might want to check the 5 and 7 plug wires, they should have a fair bit of separation but in the photo they look like they're very close or even touching in a couple of places.

View attachment 18543

Pretty engine!

Not touching. You are just seeing the 4 wire organizer on edge. There are 2 wire & 4 wire black organizers is the photo.

 

[Wally]

Good find, Wally. Absolutely should be posted in Resources.

Just posted in resources, Thanks

 

[Richard RV]

Not touching. You are just seeing the 4 wire organizer on edge. There are 2 wire & 4 wire black organizers is the photo.

Okay, good. Better safe than sorry.

In the photo it looked like where 5&7 crossed over behind the valve cover and right at the distributor they were very close or even touching.

Parallel and too close is also an issue. More space between more better in my book.

 

[RF_Burns]

So #7 would be firing 90 degrees too early if this was happening. Maybe that would explain why a spun bearing always seems to occur with #7.

 

[Tybalt39]

Had to build a new fusible link. I took the coach out of storage this evening and after driving 100 feet or so, the entire vehicle shut down. No key buzzer or starter function. I had full 12 volts at the battery and also the terminal on the firewall. There was also 12v at the horn relay. Apparently Kelvin had the same issue a few weeks ago. When I contacted him, he suggested a jumper wire between the firewall stud and the horn relay. That got everything running again. He then built a new fusible link and we installed it in just a few moments. Almost had a ruined weekend.

 

[RF_Burns]

Since you measured 12V at the horn relay terminal, that would suggest the Fusible was good, however you likely had the key OFF so there was no load through the fusible link. Some corrosion had created some resistance rather than a complete open circuit. Adding a load like the running lights would have shown near zero volts at the horn relay terminal.

However it begs the question, what caused the fusible link to fail. Was it 50 years of fatigue, or is there actually an abnormal current draw? After sitting over the winter in storage it could have been fatigue or corrosion... or rodents eating wire insulation that caused an intermittent short.

Best to have a spare fusible link with you in case of an intermittent short.

 

[Tybalt39]

I also wonder why it chose that moment to fail. I take the vehicle out of storage at least two or three times every month. I had just driven it about a week and a half earlier. Upon inspection, the ring terminals were relatively clean. Apparently, in both my case and Kelvin's, it was simply the age of the fusible link. I agree that one or two spares of fusible links is cheap insurance. I also plan to build a temporary jumper wire, just in case. If nothing else, I always carry large diameter 10GA crimp style ring terminals and 10GA wire, just to get me home.

I also just realized that at various times I was showing almost zero volts at the Horn relay. At first I thought I had no voltage, then I had 12 volts. Upon thinking about it, I remembered I had my turn signal on and it was flashing. Going with your thought, that would explain why sometimes I showed 12 volts and sometimes I showed almost nothing. At the time, I thought I was hitting corroded areas on the bolt when making my voltage measurement. Apparently, the fusible link was just barely making contact but would fail under load.

 

[Bhart]

My fixture for supporting the engine while removing the tranny was rusted.



I sprayed the metal with phosphoric acid and let set for 20 minutes. Diluted the phosphoric acid to 30%
The phosphoric acid changes the iron oxide to ferric phosphate (Black) and neutralizes the rust.


Painted the fixture with Farm and Implement gloss black spay paint from Walmart.
Phosphoric Acid from Amazon

Phosphoric Acid 85% (32 Oz / 946 mL) 85% Phosphoric Acid – Food Grade, Technical Grade Liquid – Rust Remover, Metal Cleaner, pH Adjuster, DIY Applications: Amazon.com: Industrial & Scientific

Phosphoric Acid 85% (32 Oz / 946 mL) 85% Phosphoric Acid – Food Grade, Technical Grade Liquid – Rust Remover, Metal Cleaner, pH Adjuster, DIY Applications: Amazon.com: Industrial & Scientific

www.amazon.com

Results

Did my engine hoist fixture as well.

 

[LQQKatJon]

Moved a Gmc today….. This GMC was
Brought to a shop to get a new transmission and engine installed…. In other words, the gmc is not the one pulling the towd..

 

[tmsnyder]

My fixture for supporting the engine while removing the tranny was rusted.

View attachment 18568

I sprayed the metal with phosphoric acid and let set for 20 minutes. Diluted the phosphoric acid to 30%
The phosphoric acid changes the iron oxide to ferric phosphate (Black) and neutralizes the rust.
View attachment 18570

Painted the fixture with Farm and Implement gloss black spay paint from Walmart.
Phosphoric Acid from Amazon

Phosphoric Acid 85% (32 Oz / 946 mL) 85% Phosphoric Acid – Food Grade, Technical Grade Liquid – Rust Remover, Metal Cleaner, pH Adjuster, DIY Applications: Amazon.com: Industrial & Scientific

Phosphoric Acid 85% (32 Oz / 946 mL) 85% Phosphoric Acid – Food Grade, Technical Grade Liquid – Rust Remover, Metal Cleaner, pH Adjuster, DIY Applications: Amazon.com: Industrial & Scientific

www.amazon.com

View attachment 18571

ResultsView attachment 18572

Did my engine hoist fixture as well.

View attachment 18573

Very nice. Why steel though? Did you run out of 80/20 after building your shop bench?

 

[Bhart]

Very nice. Why steel though? Did you run out of 80/20 after building your shop bench?

The steel frame was given to me.
After making a stand for table saw with an out-feed table, radial arm saw bench, drill press bench, toolbox bench, three roll around benches, fixture for my cutoff saw, and two 23" brackets for dual fuel pumps I have one 6-foot length of 80/20 left with stacks of smaller pieces.