1988 Gmc jimmy
- Thread starter Drysdalec
- Start date
Molson02536
New member
You can set the timing, to get you more HP and torque. 10 degrees advanced was factory, but if you advance it 12 to 15 degrees. Your engine will wake up with your exhaust modified already and intake i hope.
Here's the run down. On the passenger side of the truck under the carpet, there should be a tan wire with a black strip on it. This wire will be all by itself-it will not be part of a harness. There will be a connector to seperate the wire. You will need to do this prior to checking and adjusting the timing if necessary.
Got the ESC wire disconnected? Ok, now connect the inductive pick up on your timing light to the #1 spark plug wire. On your truck it should be the plug on the passenger side at the very front of the truck. Start the truck and look for the timing mark on the harmonic balancer. It will have a slot cut into it about a 1/16" of an inch wide. Make sure you WATCH OUT for the fan blades as they will be rotating VERY close to where you need to aim the timing light!
There will be a "saw tooth" looking deal (it will be on the driver's side of the truck at the bottom) that you will use to check/adjust the timing. As you look at the "saw tooth" you will notice that the "teeth" on the far right side have a "gap" between them. That is where you want the mark on the harmonic balancer to be at. Your timing should be 10 degrees advanced also but, check the VECI sticker on the sheet metal that goes over top of the radiator to double check.
If it the timing is off, the real "fun" begins. The problem is the distributor hold down bolt is a real PITA to get to. You will have to remove your coil in order to even get at it. The coil is the transformer looking deal bolted by the firewall. Getting that off is "fun" too as some of the bolts are hard to get on.
Everything is 10mm if I remember correctly. Now, get yourself a REALLY long extension and loosen the bolt at the bottom of the distributor (not as easy as it sounds!). Some people use a crow's foot or a wrench that is made specifically for this task but being that I had neither, make due with what you have. Not really hard with a long extension and ratchet IMO. Don't 100% remember what size the distributor bolt was, think it was either 9/16" or 15 mm.
Loosen the bolt just enough to turn the distributor and no more. With the knob on your timing light set to 10 degrees and work your way up with no more then 15 degrees, rotate the distributor one way or the other to get the timing mark in the "sweet spot". You can do it yourself (I did) but it's easier when another person can turn it while you observe where the timing mark is.
Once you get it, turn the truck off and tighten the distributor bolt down. Before you bolt the coil back up, check the timing one more time to confirm that it didn't change any when you tighened down the bolt. Finally, reconnect the ESC wire that you disconnected earlier. Congratulations, you just adjusted the timing on your truck! If there is anything else ya wanna know, just ask. Note: that with the advance timing you have set, your going to have to start using a higher octane fuel rating.
Larger ratio roller rockers from crane cams should provide a reasonable increase in power. The 1.6 ratio roller rockers act as if it has a larger lift camshaft. The roller rocker tip also slows wear and creates less friction, using less power. A camshaft makes more power but requires a little more work than the rocker arms. The stock ratio is 1.5, or 1.52. If you have the sbc rockers on hand, you can just slap them on and check to see if everything fits. I know jegs and i think summit sell roller tipped rockers, and full roller rockers for the 2.8.
You will have to retain your stock pivot ball and nuts if you go with SBC stuff. As our rocker arms have a M10 stud with metric threads. SBC stuff is all 3/8ths and standard threads. Or you can just buy Comp Cams' 1.6:1 ratio Magnum Roller tip rocker arms that are made for the 60v6. pn: 1414-12 for 1.6:1 (1.52:1 roller tips are 1413-12) If you are putting on 1.6:1 ratio rockers, You WILL need new springs to take the extra lift.
You may also want to think about swapping out your servo in your 700R4 with a corvette servo. They only go for around $45.00 and I've seen the servo on Summit as well as several transmission parts sites for under $25 including all the seals. Less on Ebay, you can swap them out without dropping the transmission oil pan.
http://sethirdgen.org/servo.htm
Here is also a link on how to swap out your throttle body with the throttle body from a 4.3.
http://members.shaw.ca/betterthanyoutoo/how-to/28to43tb/28to43.htm
Last edited:
Molson02536
New member
GM 2.8L/ 3.1L 60 degree V6 ENGINES
GM 2.2L L4 ENGINES (97 –EARLIER ONLY)
COMPETITION CAMS offers MAGNUM Roller Tip Rocker Arms. Available in a 1.52:1 ratio. Part #1413-12 and 1.6:1ratio. #1414-12 These rocker arms are a stiffer construction rocker arm that have a roller tip that Competition Cams claims a 10-30 hp increase over stock, -due to the increased stiffness and the reduced friction of the roller tip.
CRANE CAMS offers a full roller rocker. It is their GOLD RACE Extruded Narrow Body roller rocker. (For 60* v6 and center bolt v8 engines) it is an all aluminum needle bearing roller fulcrum and roller tip rocker. $$$ Very pricey. It is available in a 1.5:1 #25750-12 and 1.6:1 ratio #25759-12 but require cranes replacement nuts #99795 and studs #99148-12.
All part numbers are for the V6 engine, the –12 behind each number indicates quantity of 12. For the four cylinders purchasing two sets (24 rocker arms total) will work out to enough to do 3 engines, (8 rockers an engine) so if three people went together and bought two sets of rockers you will save some money.
WHAT EFFECT DOES A ROLLER ROCKER/DIFFERENT RATIO ROCKER HAVE?
With 1.5:1 or 1.52:1 ratio roller rockers the benefits are around 5 hp. due to reduced friction. With the 1.6:1 ratio rockers, you’re looking at more hp gain because the higher ratio acts like a bigger camshaft by opening the valve more. Thus allowing more air into the engine. Expect around 10-20hp. Remember be conservative these are estimated horsepower gains – depending on application power increases vary. Just because you swapped in these rockers does not guarantee that you gained 20hp.
L4
The cam lift of the 95-97 cams is .288" the amount of valve lift for the different ratios are:
1.5 (stock)= 0.432" valve lift
1.52 = 0.4377" valve lift
1.6 = 0.4608" valve lift
V6
Cam specs for a 92 3.1L
Lobe lift intake .2626"
Lobe lift exhaust .2732"
1.5 (stock)= .3939"int. .4098"exh.
1.52 = .3991"int. .4152"exh.
1.6 = .420"int. .437"exh.
To find valve lift from any cam when using different rocker arms take the known valve lift example .425" and divide by the rocker ratio 1.5. .425/1.5 = .283333333333 this is the cams lobe lift, then take the new ratio example 1.6 and multiply it by the lobe lift. .283"x 1.6 = .453" valve lift.
Valve lift – the amount the valve opens due to the combined lift of the cam and mechanical advantage of the rocker arm.
Camshaft lobe lift- the amount the camshaft lobe is raised up from its base circle.
WHAT ELSE DO YOU NEED?
If going with the Comp Cams rockers, The first thing you need to do for this swap is get a set of M10 rocker arm studs from a 2.8 v6, gm part number for these studs is #476530. These studs were sourced from an 89 2.8L Chevy celebrity. At my dealership (in Canada), they retail for $5.55 Canadian each. V6's will need 12, four cylinders will need 8 of them. The threads on these studs are M10x1.5x9.9/M10x1x18 these are a fully adjustable stud that were used on the v6s. These studs will compensate for the different ratio rocker. The stock rocker studs are non-adjustable and are a M10x1.5x9.9/M8x1x.32 the M8 non-adjustable stud will NOT work with these rockers. The Comp Cams rockers come with new 10mm nuts.
If using the Crane full roller rockers then you need to get cranes studs 99148-12 -which have a M10x1.5x9.9/ 3/8x24 stud. In addition, cranes nuts #99795. These studs use have the metric threaded end for the cylinder head and a standard type 3/8 stud/thread for the rocker arm. Don’t forget you can always check the wrecker’s for the GM studs used for the Comp rockers. I purchased six studs for six bucks from a local wrecker.
If installing the higher lift 1.6:1 rockers or installing an aftermarket performance cam along with any of the roller rockers you will also need a set of aftermarket high performance valve springs to accommodate the higher lift.
Comp Cams #’s 980-12 (springs) 742-12 (spring retainers) and 601-12 (valve locks)
Crane Cams #’s 99848-12 (springs) 99915-12 (spring retainers) and 99041-12 (valve locks)
These part numbers are for V6 engines only. However, with a little searching around, some after market replacements could be found for the L4. The stock springs for the L4 engine WILL work with the 1.6:1 rockers. There are a few companies said that these springs will be fine for that amount of lift on the 2.2L. New push-rods are a must, as the old push-rods and rockers have worn specifically to each other and using old push-rods with new rockers can cause premature wear along with voiding the warranty of the rocker arms from the company. Factory (stock type) push-rods will work fine.
*NOTE V6 owners. -Some of the earlier v6’s came with the adjustable M10 studs, some didn’t it depends on year. Check if your engine already is equipped with them before you go and buy a set to find out you didn’t need them.
OTHER MODIFICATIONS?
If installing a set of 1.6 ratio rockers modifications to the push-rod guide plates will have to be made. As the push-rod angle is now altered and will sit closer to the guide plate. An angle grinder with a carbide bit is the easiest and quickest way to do this.
VALVE ADJUSTMENT:
You must find top dead center (TDC) for piston number one. You can do this by removing the spark plug and by hand turning the engine over at the crank pulley until number one is at the top of the cylinder, use a screwdriver in the plug hole to feel the piston. While cranking the engine over pay attention to the rocker arms, if when the piston is moving up towards TDC and both rocker arms are not moving then the engine is on number one firing position if one of the rockers moves while coming up to TDC then the engine is on number four firing position, and needs to be cranked over one complete revolution.
ADJUSTMENT PROCEDURE FOR L4 ENGINES:
With number one piston on the firing position at TDC install the rockers on the studs, adjust the valves for number one cylinder only. Tighten in the adjusting nuts until all lash is removed. This can be determined by rotating the push-rod while turning in the adjusting nut. Once the play has been removed, turn in the adjusting nut one-half turn to center the lifter plunger. Repeat procedure for each cylinder one at a time while on the firing stroke only.
ADJUSTMENT PROCEDURE FOR V6 ENGINES:
With number one piston on the firing position at TDC install the rockers on the studs, the valves that can be adjusted are:
EXHAUST: 1, 2, 3
INTAKE: 1, 5, 6
Tighten in the adjusting nuts until all lash is removed. This can be determined by rotating the push-rod while turning in the adjusting nut. Once the play has been removed, turn in the adjusting nut one-half turn to center the lifter plunger. Now crank the engine over one complete revolution to number four firing position. These valves can now be adjusted:
EXHAUST: 4, 5, 6
INTAKE: 2, 3, 4
1.6 Rocker Arm Install For 2.2L
Tools and Parts Needed:
-18mm, 15mm, 13mm deep sockets
-15mm wrench
-A long Phillips or star screwdriver
-8mm and whatnot for to take off valve cover
-New Valve Cover Gasket
-8 studs GM part # 476530
-8 New GM Stock 2.2l push-rods GM part #10198813
-8 Comp. Cam 1.6 roller tipped Rocker arms w/8 Fulcrum washers & 8 nuts
-Comp. Cam red lubricant
-Small grinder (4” disc is all I used) of some sort or good drill bits to elongate push-rod guide plate.
-1 Liter of Motor Oil
-Some medium strength Thread Locker
Installation:
-Disconnect Battery
-Remove Air intake/alternator /plug wire (tape #’s to them so you know where they go back too!)/part of throttle body cover (plastic piece) and finally valve cover.
-Caution: DO NOT DROP ANYTHING DOWN INTO THE BLOCK----BE CAREFUL!!!
-Now remove all four spark plugs.
-Now starting with cylinder #1, use 15mm wrench, turn the crank pulley (by the 3 little bolts, which are 15mm) till you get Top Dead Center (TDC) of the compression stroke. U will know when u get there, b/c just hold your finger over the spark plug hole and you will get Pssssssst of air blowing by.
-Use a screwdriver by sticking it in the spark plug hole to feel the top of the piston. You will see how when you rotate the pulley, it will get to the top of the stroke and start to come back down again. You want it at the exact TDC. It will take a few times going back and forth, to see that you’ve got it TDC. It’s not that hard, don’t worry.
-Now, that you’ve got the valve in the right position, take off the Stover nut (rocker arm nut) and stud for b both the intake & exhaust. However, make sure you do one at a time and place them in Ziploc Baggies so you know exactly where they go if you ever install them again! Same with push-rods!! Know exactly where each one goes, and which end is up. Very Important!
- When taking off stud, it will be a little tuff, but its ok.
- Once both studs are off pull the push-rod guide plate off.
- Use grinder or drill to elongate it about 1/8” (I did and it was more than enough).
- Before installing new stud, clean out the stud holes with a paper towel as best you can.
- Now reinstall, plate with new studs. Using a little bit of thread locker on the stud.
- Torque down to 37lb/ft or just free hand it with about 70/lb on the 6” ratchet, I did
- Lube up both ends of the new push-rod with motor oil and stick in hole.
- Now lube up the fulcrum washer (the edges and bottom) with red lube and put it on the inside of the rocker arm with the nut on top.
- Tighten nut down until the play on the push-rod starts to get hard to turn with your fingers. Now turn it an additional ½ turn and Viola! You’re done one of 8!
- Add some motor oil to the top of the rocker arm where the little hole is.
- Once you’re done all 8, apply liberally the comp cam lube to the roller tipped part. Also, add some more oil to the top of the rocker arm.
- Then reinstall the valve cover and all other parts.
GM 2.2L L4 ENGINES (97 –EARLIER ONLY)
COMPETITION CAMS offers MAGNUM Roller Tip Rocker Arms. Available in a 1.52:1 ratio. Part #1413-12 and 1.6:1ratio. #1414-12 These rocker arms are a stiffer construction rocker arm that have a roller tip that Competition Cams claims a 10-30 hp increase over stock, -due to the increased stiffness and the reduced friction of the roller tip.
CRANE CAMS offers a full roller rocker. It is their GOLD RACE Extruded Narrow Body roller rocker. (For 60* v6 and center bolt v8 engines) it is an all aluminum needle bearing roller fulcrum and roller tip rocker. $$$ Very pricey. It is available in a 1.5:1 #25750-12 and 1.6:1 ratio #25759-12 but require cranes replacement nuts #99795 and studs #99148-12.
All part numbers are for the V6 engine, the –12 behind each number indicates quantity of 12. For the four cylinders purchasing two sets (24 rocker arms total) will work out to enough to do 3 engines, (8 rockers an engine) so if three people went together and bought two sets of rockers you will save some money.
WHAT EFFECT DOES A ROLLER ROCKER/DIFFERENT RATIO ROCKER HAVE?
With 1.5:1 or 1.52:1 ratio roller rockers the benefits are around 5 hp. due to reduced friction. With the 1.6:1 ratio rockers, you’re looking at more hp gain because the higher ratio acts like a bigger camshaft by opening the valve more. Thus allowing more air into the engine. Expect around 10-20hp. Remember be conservative these are estimated horsepower gains – depending on application power increases vary. Just because you swapped in these rockers does not guarantee that you gained 20hp.
L4
The cam lift of the 95-97 cams is .288" the amount of valve lift for the different ratios are:
1.5 (stock)= 0.432" valve lift
1.52 = 0.4377" valve lift
1.6 = 0.4608" valve lift
V6
Cam specs for a 92 3.1L
Lobe lift intake .2626"
Lobe lift exhaust .2732"
1.5 (stock)= .3939"int. .4098"exh.
1.52 = .3991"int. .4152"exh.
1.6 = .420"int. .437"exh.
To find valve lift from any cam when using different rocker arms take the known valve lift example .425" and divide by the rocker ratio 1.5. .425/1.5 = .283333333333 this is the cams lobe lift, then take the new ratio example 1.6 and multiply it by the lobe lift. .283"x 1.6 = .453" valve lift.
Valve lift – the amount the valve opens due to the combined lift of the cam and mechanical advantage of the rocker arm.
Camshaft lobe lift- the amount the camshaft lobe is raised up from its base circle.
WHAT ELSE DO YOU NEED?
If going with the Comp Cams rockers, The first thing you need to do for this swap is get a set of M10 rocker arm studs from a 2.8 v6, gm part number for these studs is #476530. These studs were sourced from an 89 2.8L Chevy celebrity. At my dealership (in Canada), they retail for $5.55 Canadian each. V6's will need 12, four cylinders will need 8 of them. The threads on these studs are M10x1.5x9.9/M10x1x18 these are a fully adjustable stud that were used on the v6s. These studs will compensate for the different ratio rocker. The stock rocker studs are non-adjustable and are a M10x1.5x9.9/M8x1x.32 the M8 non-adjustable stud will NOT work with these rockers. The Comp Cams rockers come with new 10mm nuts.
If using the Crane full roller rockers then you need to get cranes studs 99148-12 -which have a M10x1.5x9.9/ 3/8x24 stud. In addition, cranes nuts #99795. These studs use have the metric threaded end for the cylinder head and a standard type 3/8 stud/thread for the rocker arm. Don’t forget you can always check the wrecker’s for the GM studs used for the Comp rockers. I purchased six studs for six bucks from a local wrecker.
If installing the higher lift 1.6:1 rockers or installing an aftermarket performance cam along with any of the roller rockers you will also need a set of aftermarket high performance valve springs to accommodate the higher lift.
Comp Cams #’s 980-12 (springs) 742-12 (spring retainers) and 601-12 (valve locks)
Crane Cams #’s 99848-12 (springs) 99915-12 (spring retainers) and 99041-12 (valve locks)
These part numbers are for V6 engines only. However, with a little searching around, some after market replacements could be found for the L4. The stock springs for the L4 engine WILL work with the 1.6:1 rockers. There are a few companies said that these springs will be fine for that amount of lift on the 2.2L. New push-rods are a must, as the old push-rods and rockers have worn specifically to each other and using old push-rods with new rockers can cause premature wear along with voiding the warranty of the rocker arms from the company. Factory (stock type) push-rods will work fine.
*NOTE V6 owners. -Some of the earlier v6’s came with the adjustable M10 studs, some didn’t it depends on year. Check if your engine already is equipped with them before you go and buy a set to find out you didn’t need them.
OTHER MODIFICATIONS?
If installing a set of 1.6 ratio rockers modifications to the push-rod guide plates will have to be made. As the push-rod angle is now altered and will sit closer to the guide plate. An angle grinder with a carbide bit is the easiest and quickest way to do this.
VALVE ADJUSTMENT:
You must find top dead center (TDC) for piston number one. You can do this by removing the spark plug and by hand turning the engine over at the crank pulley until number one is at the top of the cylinder, use a screwdriver in the plug hole to feel the piston. While cranking the engine over pay attention to the rocker arms, if when the piston is moving up towards TDC and both rocker arms are not moving then the engine is on number one firing position if one of the rockers moves while coming up to TDC then the engine is on number four firing position, and needs to be cranked over one complete revolution.
ADJUSTMENT PROCEDURE FOR L4 ENGINES:
With number one piston on the firing position at TDC install the rockers on the studs, adjust the valves for number one cylinder only. Tighten in the adjusting nuts until all lash is removed. This can be determined by rotating the push-rod while turning in the adjusting nut. Once the play has been removed, turn in the adjusting nut one-half turn to center the lifter plunger. Repeat procedure for each cylinder one at a time while on the firing stroke only.
ADJUSTMENT PROCEDURE FOR V6 ENGINES:
With number one piston on the firing position at TDC install the rockers on the studs, the valves that can be adjusted are:
EXHAUST: 1, 2, 3
INTAKE: 1, 5, 6
Tighten in the adjusting nuts until all lash is removed. This can be determined by rotating the push-rod while turning in the adjusting nut. Once the play has been removed, turn in the adjusting nut one-half turn to center the lifter plunger. Now crank the engine over one complete revolution to number four firing position. These valves can now be adjusted:
EXHAUST: 4, 5, 6
INTAKE: 2, 3, 4
1.6 Rocker Arm Install For 2.2L
Tools and Parts Needed:
-18mm, 15mm, 13mm deep sockets
-15mm wrench
-A long Phillips or star screwdriver
-8mm and whatnot for to take off valve cover
-New Valve Cover Gasket
-8 studs GM part # 476530
-8 New GM Stock 2.2l push-rods GM part #10198813
-8 Comp. Cam 1.6 roller tipped Rocker arms w/8 Fulcrum washers & 8 nuts
-Comp. Cam red lubricant
-Small grinder (4” disc is all I used) of some sort or good drill bits to elongate push-rod guide plate.
-1 Liter of Motor Oil
-Some medium strength Thread Locker
Installation:
-Disconnect Battery
-Remove Air intake/alternator /plug wire (tape #’s to them so you know where they go back too!)/part of throttle body cover (plastic piece) and finally valve cover.
-Caution: DO NOT DROP ANYTHING DOWN INTO THE BLOCK----BE CAREFUL!!!
-Now remove all four spark plugs.
-Now starting with cylinder #1, use 15mm wrench, turn the crank pulley (by the 3 little bolts, which are 15mm) till you get Top Dead Center (TDC) of the compression stroke. U will know when u get there, b/c just hold your finger over the spark plug hole and you will get Pssssssst of air blowing by.
-Use a screwdriver by sticking it in the spark plug hole to feel the top of the piston. You will see how when you rotate the pulley, it will get to the top of the stroke and start to come back down again. You want it at the exact TDC. It will take a few times going back and forth, to see that you’ve got it TDC. It’s not that hard, don’t worry.
-Now, that you’ve got the valve in the right position, take off the Stover nut (rocker arm nut) and stud for b both the intake & exhaust. However, make sure you do one at a time and place them in Ziploc Baggies so you know exactly where they go if you ever install them again! Same with push-rods!! Know exactly where each one goes, and which end is up. Very Important!
- When taking off stud, it will be a little tuff, but its ok.
- Once both studs are off pull the push-rod guide plate off.
- Use grinder or drill to elongate it about 1/8” (I did and it was more than enough).
- Before installing new stud, clean out the stud holes with a paper towel as best you can.
- Now reinstall, plate with new studs. Using a little bit of thread locker on the stud.
- Torque down to 37lb/ft or just free hand it with about 70/lb on the 6” ratchet, I did
- Lube up both ends of the new push-rod with motor oil and stick in hole.
- Now lube up the fulcrum washer (the edges and bottom) with red lube and put it on the inside of the rocker arm with the nut on top.
- Tighten nut down until the play on the push-rod starts to get hard to turn with your fingers. Now turn it an additional ½ turn and Viola! You’re done one of 8!
- Add some motor oil to the top of the rocker arm where the little hole is.
- Once you’re done all 8, apply liberally the comp cam lube to the roller tipped part. Also, add some more oil to the top of the rocker arm.
- Then reinstall the valve cover and all other parts.