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#1418554 Wed Jul 28 2021 09:51 PM
Joined: Feb 2013
Posts: 284
This is on my '48 GMC, 228 engine. The heat riser is stuck and I've been trying to get it freed up with no luck so far. I have the exhaust system off for some new pipe and took the opportunity to look at the flap position inside the manifold. Am I correct in thinking that the flap should be completely closed? The picture shows it doesn't fit flush, with an opening about 3/8" wide. One of the quirks of this truck is that after the engine is completely warmed up it will only idle for a few minutes then slowly die out. I'd like to get the flap free and restore its proper function and it would be great if it solves my weak idle problem at the same time. What do you think?

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Joined: Mar 2014
Posts: 3,646
You can get that open by using penetrating oil (think Liquid Wrench, Kroil, etc). Spray the shafts (in and out). Let it sit a while and then gently tap with a small hammer until you feel it start to move when you wiggle the counterweight. Or at least that's how I usually do it. Some claim you can heat the manifold up, quench it and that will free it, but that trick never worked for me. But I figure somebody will show up in 10, 9, 8, 7, 6 seconds and tell you to do something else. In my opinion you mostly want to let the penetrating oil do the work, wiggling a bit to help it along. It may take a while, however it took a while for it to get in this condition...Good luck! Years ago there was a penetrating oil made here in Texas that was a real treat to use and would free something like that up in a minute or two but the company closed.


1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Joined: Jul 2014
Posts: 1,344
Moderator for Tons o' Fun , Co-Moderator Driveline Forum
Jon - agreed, the Kroil or Liquid wrench and tap, tap, tap on each end of the shaft towards the center back and forth, while applying turning force on the counterweight. Go slowly and you'll finally get it freed up. Patience is your friend on this one.

Ron - - Dusty53
"you can't dance with the Devil and then wonder why you're still in Hell"
" They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel"

1954 Chevy 3604
In the Gallery Forum
Joined: Dec 2013
Posts: 1,123
Former BMW Rider
Eureka Jim,

If it doesn't free up to your satisfaction, you can always rebuild it. Check this out. (CLICK)


His: 1947 Chevrolet 3104 []
Hers: 2008 American Saddlebred []

"I proudly Stand for the Flag and Kneel for the Cross" Unknown

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