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Old 02-12-2022, 12:58   #1
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Perkins 4-108 starting in cold vs warm state

Ive recently rebuilt my engine, changed the balance disc and lapped the valves and it runs great. Ive been using it to charge batteries with a mechman high output alternator which works great and will put out a nice charge at very low RPM.
My question is about the start-up which is instant with a warm engine or if its been run within ten or twelve hours. But on startup after sitting overnight, sometimes it can be fairly stubborn even though the boat is kept above 50 degrees and I understand that a really cold engine can be very difficult to start. But it seems that the injection system is the culprit rather than engine temp. What seems to be happening is a bleed-down of injection pressure, so that the engine must crank for about 30 seconds to build enough pressure to start and then it tends to miss a bit, just at first on low throttle.
Im wondering if there is a check valve in the injection pump that could have corrosion or some impurity causing it to leak down.
Ive been considering an engine block heater to assure that starting is easy and quick, but I suspect the reason for the harder starts is not attributable to temperature but rather a fuel pressure issue.
One for the experts.
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Old 02-12-2022, 13:15   #2
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Re: Pwekins 4-108 starting in cold vs warm state

I would check that all lines in and out along with bleed ports are tight and closed. Mine has trouble cold starting as well at those temps and having not been started for weeks. Cold, ours will take a few extra rotations to catch but then goes with no issue. During the summer months it generally starts right away. I would also adjust the Hp pump timing. May need to be adjusted if it hasnít been in a long time.
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Old 02-12-2022, 13:23   #3
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Re: Pwekins 4-108 starting in cold vs warm state

Does your 108 have glow plugs? Some did and helps w/a cold start.

Could it be your new high output alternator slowing the cranking?

Just throwing things out there. Is this something new after the rebuild?
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Old 02-12-2022, 13:25   #4
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Re: Pwekins 4-108 starting in cold vs warm state

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Does your 108 have glow plugs? Some did and helps w/a cold start.

Could it be your new high output alternator slowing the cranking?

Just throwing things out there. Is this something new after the rebuild?
No glow pugs for 4-108 just the cold start mechanism but would help for sure.
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Old 02-12-2022, 13:46   #5
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Re: Pwekins 4-108 starting in cold vs warm state

Yes you are correct, it is a cold start system/aid with some heater core components instead of true glow plugs.
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Old 02-12-2022, 14:36   #6
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Re: Pwekins 4-108 starting in cold vs warm state

The 4/108 is an indirect injection engine,so it needs a little HEAT to fire from cold ,a couple of 10 second bursts on the starter will generally do this or use the cold start as fitted ,which heats the inlet air ,not a fuel problem in most cases.⛵️⚓️
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Old 02-12-2022, 14:49   #7
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Pwekins 4-108 starting in cold vs warm state

Doog, youíre right about the case drainback from the injector pump, at the point where the supply line enters the pump head thereís a tiny shuttle valve and 2 springs that allows lift pump pressure access for priming and when the transfer (vane) pump turns (cranking) the shuttle is sent to the other side. If it gets stuck, the vane pump has trouble making case pressure. A worn vane pump can also be the problem with hard starting. The lift pump also acts a a non return valve on the supply line but the return line is usually a clean run to the tank so if the tank is below the injector pump it can drain back.
Some 4-108ís did indeed have 4 glow plugs and ďParts4enginesĒ has em for £38 each.
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Old 02-12-2022, 14:56   #8
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Re: Pwekins 4-108 starting in cold vs warm state

I think my 4-107 has a glow plug on the intake to heat the fuel going in. If the 4-108 is the same, I would check to make sure that glow plug is working.
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Old 02-12-2022, 18:01   #9
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Re: Pwekins 4-108 starting in cold vs warm state

rbk, will certainly look into the pump timing. Now if you mean the injector timing set by the gear under the timing cover, of course on rebuild it was carefully adjusted and I ran Standodyne cleaner through the system. Its all good.
I just had a comment about oil and Ive put Shell Rotella t-6 in the engine and just learned this is not good, the synthetic can cause issues and Im changing it out ASAP! An old engine needs the traditional oil so Im going back to Delo and maybe that's a factor.
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Old 02-12-2022, 18:07   #10
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Re: Pwekins 4-108 starting in cold vs warm state

Thanks skipperpete, I think you nailed it! Yeah, no glow plugs here and the motor has always started well but only with a very well charged battery.

Ive put Rotella t-6 in the engine and I think on reading an article on marine engines this is a bad idea and going to change out ASAP for Delo. The engine always runs low RPM and cool temperatures and from what I just read a synthetic can really mess up an engine operating like this.

Thanks for the tips!
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Old 02-12-2022, 18:10   #11
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Re: Pwekins 4-108 starting in cold vs warm state

To time the FI pump. You’d need to loosen the three bolts holding the pump to the engine and then twist the pump to tweak the timing.
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Old 02-12-2022, 19:33   #12
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Re: Pwekins 4-108 starting in cold vs warm state

Quote:
Originally Posted by doog View Post
rbk, will certainly look into the pump timing. Now if you mean the injector timing set by the gear under the timing cover, of course on rebuild it was carefully adjusted and I ran Standodyne cleaner through the system. Its all good.
I just had a comment about oil and Ive put Shell Rotella t-6 in the engine and just learned this is not good, the synthetic can cause issues and Im changing it out ASAP! An old engine needs the traditional oil so Im going back to Delo and maybe that's a factor.
See marchsmith said regarding adjusting the Hp pump. Make absolutely sure there is an initial mark on both the pump and the block. If not use a sharp blade (razor) and scribe a good one across both with a straight edge. You can adjust it while itís running.

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Re: Pwekins 4-108 starting in cold vs warm state
To time the FI pump. Youíd need to loosen the three bolts holding the pump to the engine and then twist the pump to tweak the timing.
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Old 02-12-2022, 20:26   #13
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Re: Pwekins 4-108 starting in cold vs warm state

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Originally Posted by doog View Post
Thanks skipperpete, I think you nailed it! Yeah, no glow plugs here and the motor has always started well but only with a very well charged battery.

Ive put Rotella t-6 in the engine and I think on reading an article on marine engines this is a bad idea and going to change out ASAP for Delo. The engine always runs low RPM and cool temperatures and from what I just read a synthetic can really mess up an engine operating like this.

Thanks for the tips!


Do the lift pump valves first, thatís an easy job , the injector pump valve is a much bigger project partially due to the pump access under the exhaust manifold or heat exchanger.
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Old 02-12-2022, 20:44   #14
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Re: Pwekins 4-108 starting in cold vs warm state

I have a 4108 running a 14kw generator. In cold weather it takes several revolutions. But by using glow plugs or a hair dryer pointed into the intake, it starts right away.
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Old 02-12-2022, 21:11   #15
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Re: Perkins 4-108 starting in cold vs warm state

Never tried a hairdryer Doesn’t sound like a bad idea
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