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Old 06-03-2021, 16:16   #1
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Adjust valves Perkins 4108

I’ve adjusted valves on many air cooled engines, but this is first attempt on diesel. According to manual, key is to position one cylinder in valve “overlap”, which then sets another “target cylinder “ in tdc, ready for valve adjustment. I am using starter to try to bump engine into overlap, unsuccessfully. The engine never stops at right place. I’m thinking another approach is when an exhaust or intake valve is substantially open, then the companion valve on same cylinder should be positioned for clearance check. This position is much easier for me to achieve. What do you think?
I must be missing something. A routine maintenance task should not be this difficult. Thanks for any suggestions. Tom
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Old 06-03-2021, 16:35   #2
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Re: Adjust valves Perkins 4108

Use a socket and a breaker bar on the crank nut to rotate the engine manually. If you pull out the injectors you can spin it over by hand.

If you take out the starter you can move the engine by the flywheel teeth.

If you have the rocker on the base circle sure but trying to do it by movement of just the intake might not be accurate.


https://mgispeedware.com/wp-content/...ft-overlap.jpg
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Old 06-03-2021, 16:55   #3
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Re: Adjust valves Perkins 4108

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Originally Posted by Tom1340 View Post
I’ve adjusted valves on many air cooled engines, but this is first attempt on diesel. According to manual, key is to position one cylinder in valve “overlap”, which then sets another “target cylinder “ in tdc, ready for valve adjustment. I am using starter to try to bump engine into overlap, unsuccessfully. The engine never stops at right place. I’m thinking another approach is when an exhaust or intake valve is substantially open, then the companion valve on same cylinder should be positioned for clearance check. This position is much easier for me to achieve. What do you think?
I must be missing something. A routine maintenance task should not be this difficult. Thanks for any suggestions. Tom
If you put the two valves rocking on #1 you can then adjust both valves on #4 and whatever is not compressed on #2 and #3. Then get #4 rocking and adjust both on #1 and whatever is loose on #2 and #3. In theory you can adjust all 8 valves in two revolutions of the crankshaft.

You could try a strap type filter wrench on the crank pulley or the water pump pulley while holding the belt tight.

Or try a starter button and just "tap" the starter to get the valves where you want them but it's kind of tough on the bendix/flywheel and solenoid this way.

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Old 06-03-2021, 18:05   #4
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Re: Adjust valves Perkins 4108

Thanks Scuba. I’ll try the breaker bar and socket tomorrow. The engine is in backwards, and accessing the crank nut requires gymnastics. Hopefully the available space and breaker will work. Pulling the injectors is very low on my wish list.
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Old 06-03-2021, 19:11   #5
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Re: Adjust valves Perkins 4108

Indeed, "Boat Yoga" comes to mind. Once you get a socket on it it'll go easy.

If you can reach the face of the crank pulley there may be threaded holes in it for a puller. If you put bolts or rods in the holes you can then use a prybar/long stick/screwdriver to move the pulley. If you get near TDC (within about 45* of TDC) of both the valves rocking (which is around TDC) the opposite valves at 1/2 the firing order (1-3-4-2) should still be adjustable as they should still be on the base circle. I.E rock both valves on cylinder #1, adjust both valves on cylinder #4, Rock #2, adjust #3. When cranking it will be exhaust then the intake opening. If you are still on the intake opening you're probably OK to adjust the opposite cylinder. If the intake valve is closing you may not be on the base circle.

If you do the close to TDC method on #1 do not adjust the valves on #3 or #2 cylinders, only the #4 valves. You can only adjust 4 valves at once if you are at TDC.

Hope this makes sense. Fix I can do writing about how to fix, not so much.
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Old 07-03-2021, 09:40   #6
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Re: Adjust valves Perkins 4108

Hmmm...there is no exposed crank nut. A 2nd pulley (unused) has been added and there is a 1-1/2 inch keyed shaft hiding the nut. See photo. I can try to remove 2nd pulley and try to access nut, but not sure what I’ll find or what I’ll damage. Other option is to try belt or chain wrench on shaft, or even a pipe wrench. Ideas?
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Old 07-03-2021, 09:49   #7
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Re: Adjust valves Perkins 4108

Take off second pulley
or
Use a pipe wrench or similar
or
use a bar of screw driver with square stock between bolt heads and center shaft to turn the crank
or
buy a starter button
or
take out starter and use flywheel teeth
or
drill hole in bell housing to gain access to flywheel teeth
or
hold my beer
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Old 07-03-2021, 11:45   #8
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Re: Adjust valves Perkins 4108

Quote:
Originally Posted by Scubaseas View Post
Use a socket and a breaker bar on the crank nut to rotate the engine manually. If you pull out the injectors you can spin it over by hand.

If you take out the starter you can move the engine by the flywheel teeth.

If you have the rocker on the base circle sure but trying to do it by movement of just the intake might not be accurate.


https://mgispeedware.com/wp-content/...ft-overlap.jpg
Just take your time and be sure to check that the valves are completely closed before adjusting.
If you encounter some resistance turning by hand, give it 10 sec. Then nudge it a bit more.
One at a time, doesn't have to be sequential.
Don't adjust to tightly.
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Old 07-03-2021, 11:50   #9
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Re: Adjust valves Perkins 4108

Quote:
Originally Posted by Tom1340 View Post
Hmmm...there is no exposed crank nut. A 2nd pulley (unused) has been added and there is a 1-1/2 inch keyed shaft hiding the nut. See photo. I can try to remove 2nd pulley and try to access nut, but not sure what I’ll find or what I’ll damage. Other option is to try belt or chain wrench on shaft, or even a pipe wrench. Ideas?
As mentioned, Chain wrench or belt, you could fashion a spanner wrench to fit over those exposed bolts to rotate as well.
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Old 07-03-2021, 11:57   #10
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Re: Adjust valves Perkins 4108

Quote:
Originally Posted by Tom1340 View Post
I’ve adjusted valves on many air cooled engines, but this is first attempt on diesel. According to manual, key is to position one cylinder in valve “overlap”, which then sets another “target cylinder “ in tdc, ready for valve adjustment. I am using starter to try to bump engine into overlap, unsuccessfully. The engine never stops at right place. I’m thinking another approach is when an exhaust or intake valve is substantially open, then the companion valve on same cylinder should be positioned for clearance check. This position is much easier for me to achieve. What do you think?
I must be missing something. A routine maintenance task should not be this difficult. Thanks for any suggestions. Tom



It never does, I use a screwdriver on the starter ring to get exact tDC.
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Old 07-03-2021, 12:12   #11
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Re: Adjust valves Perkins 4108

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Originally Posted by Boatyarddog View Post
As mentioned, Chain wrench or belt, you could fashion a spanner wrench to fit over those exposed bolts to rotate as well.
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Excellent point, just don't break a bolt as the crank would then be unbalanced. Use a wrench between the bolt and the center shaft? Sure. Even a oversized combo or box end wrench would work fine for this. Good point on wait ten seconds and nudge again. 13:1 compression ratio makes it hard to crank over. And to stop in one place you want it to.

As long as the valve is closed is the rub. Valve has to be on it's base circle for any adjustment to be accurate. You don't need a timing card to do this.

I suggested "rocking" two valves as this has you at or near TDC. It's called valve overlap and I would be very surprised if it did not happen at TDC on a 4-108 engine. If you can get near where two of the valves on a cylinder are both moving you can confidently adjust the opposite cylinder. For cyl #1 rocking you could adjust cylinder #4. If #2 rocks you can do #3, etc.

If you can get it to TDC of any cylinder you can then confidently adjust any valve that's loose (assuming the valves were not more than .012 or so too tight in the first place) then do it's opposite cylinder. 1 is opposite 4 and 2 is opposite 3 and vice versa and the firing order is 1-3-4-2 .
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Old 07-03-2021, 15:31   #12
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Re: Adjust valves Perkins 4108

Aaaha! Job is done. I initially did not intend to rotate engine manually as I was under impression that it would take 100 ft-lbs torque in a very confined space. But when I started to remove the 2nd pulley, I found the engine rotated easily, maybe 15 - 20 ft-lbs. it was easy to stop on tdc and valve overlap.
Thanks scuba, dog, and chas for sharing your insight.
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