Quick valve adjustment question 250 I6 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mrnkc130 · 10-09-2016, 03:13 PM

I have a 1978 c10 with a 250 and a 3 on the tree, I dont have a manual for it and my googling has gotten me some conflicting answers (most info based off car engines not sure if they are different like older 235's)

Is the best valve adjust procedure (while running) loosen until there is a slight noise then tighten until no clatter, then 1 more full turn? Or better to adjust static with feeler gauges? if so do you know the spec on that?

Appears to be original motor, i have some rebuild paperwork from 10 years ago that was in the glove box..This is just a running around truck that is almost completely stock and straight with no rust issues (bad paint job though!)

Thanks for the help, this is my 1st square body truck.

D13 · 10-10-2016, 06:07 AM

Running, loosen rockers until just starts to clatter, then tighten 3/4 turn or so. Lifters are hydraulic self adjusting and trying to do it static is a bigger PITA than the little bit of oil mess.

If you can find a space valve cover and cut the top off for access that's even better. Being a 78 it should be integral head so be careful, valve covers for those are different than for the earlier models.

mrnkc130 · 10-10-2016, 09:19 AM

It is NOT an integral head, which is where I'm getting some of the ambiguity about the valve lash adjustment.
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cadillac_al · 10-10-2016, 10:12 AM

I would do it while running too.

mrnkc130 · 10-10-2016, 11:09 AM

Ok thanks, I just wanted to double check that possibly since it was a truck engine and not integral head it didn't possibly have solid lifters like my 235's and need a static adjustment. Thanks everyone!

This thing rides great compared to the older chevys I'm used to, I really like this old workhorse!
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mrnkc130 · 10-18-2016, 03:33 PM

That took care of my miss, runs much better now.
I bought a rebuild kit for the monojet carb as well, but I was thinking maybe I'd just replace the whole thing if there is a better option? There is all sorts of vacuum lines plugged on this thing and the electric idle deal must be bad because if it's plugged in it idles super fast and won't go down.

Ideas for a new simpler carb without all junk on it that works with my throttle linkage and maybe a simple mech or electric choke?

Thanks!
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**hatzie** · 10-18-2016, 06:31 PM

The high idle solenoid should only be powered in a few situations not all the time. I believe it's part of the TCS (Transmission Controlled Spark) system on the early I6 engines. On some V8 trucks it was triggered by the AC clutch engagement circuit.
It should run fine without it.

Gmc.guy · 10-20-2016, 10:29 AM

The idle stop solenoid is adjustable. It helps stop dieseling when you shut it off. On my 74 and my yard truck it gets hot power with the key on. You can screw the solenoid out to turn it down so that it doesn't affect the idle speed (there's a hex head on the end) It just lets the throttle blades close all the way with the key off. It shouldn't change the idle speed, just lets it idle It should be completely independent of the tsc I have 3 250's and the both engines I run will not idle without that hot power to the solenoid Fast idle should be in your linkage and work together with the choke

10-09-2016, 03:13 PM	#1
mrnkc130 Registered User Join Date: Jun 2016 Location: Justin, TX Posts: 18	Quick valve adjustment question 250 I6 I have a 1978 c10 with a 250 and a 3 on the tree, I dont have a manual for it and my googling has gotten me some conflicting answers (most info based off car engines not sure if they are different like older 235's) Is the best valve adjust procedure (while running) loosen until there is a slight noise then tighten until no clatter, then 1 more full turn? Or better to adjust static with feeler gauges? if so do you know the spec on that? Appears to be original motor, i have some rebuild paperwork from 10 years ago that was in the glove box..This is just a running around truck that is almost completely stock and straight with no rust issues (bad paint job though!) Thanks for the help, this is my 1st square body truck. __________________ 1978 c10 2wd 250/ 3spd 1966 C20 283/sm420 1946 Chevy 2Ton 235/4spd

10-10-2016, 06:07 AM	#2
D13 Registered User Join Date: Feb 2007 Location: Memphis MI Posts: 1,851	Re: Quick valve adjustment question 250 I6 Running, loosen rockers until just starts to clatter, then tighten 3/4 turn or so. Lifters are hydraulic self adjusting and trying to do it static is a bigger PITA than the little bit of oil mess. If you can find a space valve cover and cut the top off for access that's even better. Being a 78 it should be integral head so be careful, valve covers for those are different than for the earlier models. __________________ 1987 2 ton 1982 250/TH350 beater in progress Dad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrapping Plus a mess o' tractors

10-10-2016, 09:19 AM	#3
mrnkc130 Registered User Join Date: Jun 2016 Location: Justin, TX Posts: 18	Re: Quick valve adjustment question 250 I6 It is NOT an integral head, which is where I'm getting some of the ambiguity about the valve lash adjustment. Posted via Mobile Device

10-10-2016, 10:12 AM	#4
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,354	Re: Quick valve adjustment question 250 I6 I would do it while running too. __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

10-10-2016, 11:09 AM	#5
mrnkc130 Registered User Join Date: Jun 2016 Location: Justin, TX Posts: 18	Re: Quick valve adjustment question 250 I6 Ok thanks, I just wanted to double check that possibly since it was a truck engine and not integral head it didn't possibly have solid lifters like my 235's and need a static adjustment. Thanks everyone! This thing rides great compared to the older chevys I'm used to, I really like this old workhorse! Posted via Mobile Device

10-18-2016, 03:33 PM	#6
mrnkc130 Registered User Join Date: Jun 2016 Location: Justin, TX Posts: 18	Re: Quick valve adjustment question 250 I6 That took care of my miss, runs much better now. I bought a rebuild kit for the monojet carb as well, but I was thinking maybe I'd just replace the whole thing if there is a better option? There is all sorts of vacuum lines plugged on this thing and the electric idle deal must be bad because if it's plugged in it idles super fast and won't go down. Ideas for a new simpler carb without all junk on it that works with my throttle linkage and maybe a simple mech or electric choke? Thanks! Posted via Mobile Device

10-18-2016, 06:31 PM	#7
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,933	Re: Quick valve adjustment question 250 I6 The high idle solenoid should only be powered in a few situations not all the time. I believe it's part of the TCS (Transmission Controlled Spark) system on the early I6 engines. On some V8 trucks it was triggered by the AC clutch engagement circuit. It should run fine without it. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

10-20-2016, 10:29 AM	#8
Gmc.guy Registered User Join Date: Nov 2015 Location: Alberta Posts: 464	Re: Quick valve adjustment question 250 I6 The idle stop solenoid is adjustable. It helps stop dieseling when you shut it off. On my 74 and my yard truck it gets hot power with the key on. You can screw the solenoid out to turn it down so that it doesn't affect the idle speed (there's a hex head on the end) It just lets the throttle blades close all the way with the key off. It shouldn't change the idle speed, just lets it idle It should be completely independent of the tsc I have 3 250's and the both engines I run will not idle without that hot power to the solenoid Fast idle should be in your linkage and work together with the choke __________________ -Cody



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