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1978 Blazer/Jimmy projects
- Thread starter mac907
- Start date
I have many questions to come, but first and foremost I'm hoping someone on this board can help me with the timing. Once I got everything put together the truck started and ran okay, the timing was at 23 degrees After TDC. I then looked in my factory tecnicians manual and it said "refer to timing sticker under hood", I checked my Haines manual and it said the same thing but gave 8 degrees Before TDC as a common example. I then checked my 1971 tecnicians manual that I use for my 71' Jimmy and it said 12 degrees before TDC. So, for now I have set my timing to 10 degrees Before TDC and it idles much better. I also ended up having to turn back the idle screw on the carb almost two full turns because as I advanced the timing, the rpms kept rising. Lastly, my exhaust no longer smells like gasoline. There is however a downside, my truck is now gutless off the line and has quite a bit of hesitation if I give it heavy throttle when accelerating either at low speeds or from a stop. Before I replaced all these parts and set the timing I chould chirp the tires off the line no problem.
Disclaimer: to my knowledge I did get an accurate timing reading. I capped off the vaccum advance at he carb and distributor, ran the truck to operating temp, found TDC compression stroke and marked it with timing tape on the balancer (the groove was off by a long shot sitting at 12 o' clock at TDC, plus where I put the tape coincided with the dot on the timing gears), chocked the truck and got my reading with the tranny in drive, and used the digital timing light to keep my rpm at 550, all as reccommended in the service manuals.
Disclaimer: to my knowledge I did get an accurate timing reading. I capped off the vaccum advance at he carb and distributor, ran the truck to operating temp, found TDC compression stroke and marked it with timing tape on the balancer (the groove was off by a long shot sitting at 12 o' clock at TDC, plus where I put the tape coincided with the dot on the timing gears), chocked the truck and got my reading with the tranny in drive, and used the digital timing light to keep my rpm at 550, all as reccommended in the service manuals.
My question to anyone so kind as to have read the post this far is. Do you also have a 78' chevy truck with a 350 SBC engine, and if so do you have the factory sticker under the hood? I would appreciate hearing what it says my timing should be set to. Thanks in advance.
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Thanks Mark1968, that's a little relieving regarding where I have it set. Now I'm leaning closer toward the carb being the issue. Vaccum lines are good, but I'm thinking that the drastic change in timing may give reason for a complete rebuild. I'm currently running an Edelbrock 1405 on a stock intake manifold, or I have an Edelbrock 1406 with Performer Rpm manifold on my spare engine that could be a donor.
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Where did the vacuum advance can end up in relation to the block?..reason I ask is it is possible to stab the distributor in a tooth or two (or more) off,and still be able to get it timed by turning it,but now the rotor might not be pointing directly at the plug wire post in the distributor cap..the spark now has to jump farther and might not be able to fire the plug as well under a load..
Given that there are 13 teeth on the distributor, that's just over 27 degrees per tooth. I'd say it appears by the comparison I probably need to move one tooth counter-clockwise. Thanks for the input once again diesel4me, I'll see if shifting a tooth over helps.
One concept I'm not grasping though is how the indexing of the distributor shaft will line up with the oil pump shaft once I move over one tooth since the oil pump shaft linkage is like a flat head screwdriver and can only slip together every 180 degrees.
One concept I'm not grasping though is how the indexing of the distributor shaft will line up with the oil pump shaft once I move over one tooth since the oil pump shaft linkage is like a flat head screwdriver and can only slip together every 180 degrees.
You can use a long flat blade screwdriver to rotate the oil pump or an oil pump priming tool. Meaning you can position it in any position you want, might take a few tries to get everything to index properly. But it will work.
Ahh a screwdriver makes sense, thanks livid4dirt. This will be my 1st timing actually pulling a distributor instead of just twisting it or swapping cap & rotor... a lot of 1st times with this truck actually. So far I haven't broken or blown anything major.
Keep in mind you'll have to rotate the distributor rotor a few more degrees away from where you want it to end up,due to the spiral cut gear on it that meshes with the cam gear..
After you've put in a distributor a few times,you'll find you can just get the gears "half meshed" in the correct spot to time it--and push down on it some while you crank it over with a remote starter button,and the oil pump drive slot will "click" into place and let it drop down into the block the rest of the way..saves a lot of fiddling with long screwdrivers and bending over under the hood for several minutes trying to align the pump drive..
After you've put in a distributor a few times,you'll find you can just get the gears "half meshed" in the correct spot to time it--and push down on it some while you crank it over with a remote starter button,and the oil pump drive slot will "click" into place and let it drop down into the block the rest of the way..saves a lot of fiddling with long screwdrivers and bending over under the hood for several minutes trying to align the pump drive..
Just a little FYI, the apostrophe takes the place of the missing numbers in a year.
1978 is '78, not 78'. That is 78 feet.
As for the timing, you probably have the wrong timing pointer. There are two different ones. Is yours an integral part of the timing cover, or an additional bolt on piece?
Martin
1978 is '78, not 78'. That is 78 feet.
As for the timing, you probably have the wrong timing pointer. There are two different ones. Is yours an integral part of the timing cover, or an additional bolt on piece?
Martin
I see. As far as the timing tab goes, if I recall it's the removable after market type that goes from 12 BTDC on one end to 10 ATDC on the other. Based on it's size and curvature I'm pretty sure it only mounts up to roughly the 2 o' clock position. Of the 4 trucks I have, they're all mounted the same and of the same design. If there were a a factory pointer that mounted in roughly the 12 o' clock position, then he groove on the balancer would be on. I held my balancer up to two different new ones and confirmed that the indexing between the outer groove and crank groove was the same, so I doubt balancer slippage is my issue. Also, the timing has held rock steady a 10 BTDC since I set it over 1 week & 700 miles ago.
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This image pretty much sums up what I'm talking about. The link is to a whole write up I just found on the groove and tabs not matching. My tab being bolt on, is even further clockwise in position.
http://www.crankshaftcoalition.com/wiki/Timing_Tabs_and_Damper_TDC_Lines_SBC
Paragragh 3 explains exactly what I have run into and confirms my TDC reading with respect to where I had to put my timing tape.
http://www.crankshaftcoalition.com/wiki/Timing_Tabs_and_Damper_TDC_Lines_SBC
Paragragh 3 explains exactly what I have run into and confirms my TDC reading with respect to where I had to put my timing tape.
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About the fuel tank...I once bought a tank for my old 85 K10 from MTS Plastic Tank Company and was VERY satisfied. That thing was thick and dang near indestructible.
http://www.mtscompany.com/chevy-gmc.htm
http://www.mtscompany.com/chevy-gmc.htm
