Replacing The Contacts And Plunger In A Denso OSGR Starter

To order parts please click here. To see how easy it is to repair your own starter please read on.

This post has been a long time coming and it is pretty lengthy. It pertains to repairing the clicks but will not crank sometimes failure found in Denso & Nippondenso Offset Gear Reduction Starters (OSGR) found on multiple vehicles such as Acura, Honda, Lexus, Toyota, Subaru, Isuzu, Chrysler, Dodge, Plymouth, Harley Davidson, John Deere, Caterpillar, JI Case, Kubota, Ferrari, Rolls Royce, Corvette, Late model Chevrolet and GMC Trucks and various others. The condition starts by occasionally clicking one time and having to try again and escalates up to having to try to start the vehicle dozens of times before the stater will actually work and it is distinguished by one solid click each time the key is turned with a no crank condition. Again when it starts it will generally happen once in a while and then will crank normally and eventually it gets more frequent.

Once the starter is off of the vehicle it needs to be placed in a suitable holding device such as a good bench vise. Position the starter with the drive gear facing down and the solenoid cap facing up as shown in the following picture. Remove the three retaining screws along with the support bracket for the starter motor lead which happens to be directly behind the nut driver in the picture. It shows up again later in the post.

Lift the cover. It may take tapping it up along the edge to break the seal.

With the cover out of the way you can now see the top of the plunger assembly

Lift the plunger out and position it aside.

The plunger return spring may come out with the plunger or it may stay in the starter as this one did.

You can use a small screwdriver or the plunger rod itself to grab the spring and lift it out of the starter. DO NOT LOSE THIS SPRING. The starter is junk without it.

Now would be a good time to clean some of the debris from the opening. A shop vacuum could be used but I normally just turn the starter upside down over the palm of my hand to shake most of the loose stuff out. The main reason I do this is because on earlier gas starters and most diesel starters the single ball bearing that is in the end of the starter drive can fall out and be lost. The starter will not work properly without this ball in place. It is visible in the very bottom of the hole in the picture below. This one stayed in place.

The next step is to remove the motor contact. First lift the cover to access the 12mm nut that is below.

After removing that nut lift the motor lead out of the way and remove the 14mm nut. I strongly recommend using a six point socket and make sure that you hold it securely as it is easy to slip off and damage both the nut and your knuckles.

Remove the plastic insulator and flat washer and position aside. Pull or roll the o-ring off of the bolt.

Slide the bolt into the starter and remove from the inside.

With the bolt out of the way, carefully slide the contact out from behind the solenoid flag terminal. You may have to use a small screwdriver to break the light bond between the contact and the flag terminal. It is very important to not move the flag terminal and wire any more than needed as it can be broken.

When the terminal is removed more debris will break loose and will have to be removed.

With the debris cleaned up and a new contact carefully slid in behind the flag terminal the bolt can now be installed.

Reposition the o-ring back on the stud and roll it back to the insulator edge.

Place the outside insulator over the bolt and with a slight twist motion push it over the o-ring until it seats.

Install the flat washer and the 14mm nut and snug it up finger tight. Now using a 13mm open end wrench hold the bolt on the inside being careful not to damage the flag terminal and wire lead I spoke of earlier. With a ratchet and socket tighten the outside nut to 15ft lbs. Make sure the contact stays flat on the inside of the solenoid.

Now install the 12mm nut and recheck the contact to make sure it is still laying flat. It will have probably moved some and keep this movement in the back of you mind as it will be important later.

Now it is time to replace the contact on the battery bolt. Again remove the 14mm nut.

Outside insulator.

Now push the bolt and contact to the inside of the solenoid.

With the bolt and contact removed.

Place the end of the bolt on a solid surface and lightly tap the edge of the contact.

It may take a couple of light taps to completely loosen the contact.

Slide the old contact off and position it aside.

Clean any dislodged debris from the solenoid and make sure the insulating paper is in place. Some of the earlier starters did not have this piece installed.

Place the interior insulator back into the solenoid.

Place the new contact inside and line up the holes.

Slide the bolt in from the inside.

Until the knurled edge stops the bolt.

Install the o-ring.

The outside insulator. Some of the insulator like the one below have an alignment dowel attached.

Be sure to line up the dowel to the hole during assembly or it will break.

Check the dowel alignment again before installing the flat washer and the 14mm nut.

Using a ratchet and socket ( 6 point ) tighten the nut to 15ft lbs. This will pull the knurled edge of the bolt into the contact. Also make sure that the contact is sitting flat in the solenoid during this step.

Hold the bolt with an open end wrench. Sometimes 13mm and sometimes 15mm.

During the tightening process the right inside edge will lift slightly.

I rotate the bolt until the left edge is lifted slightly. The reason for this is what I told you to remember earlier when the motor lead was reattached and that bolt rotated slightly. The same thing is going to happen when the battery cable is reattached to the bolt. The only difference is that you will not be able to adjust it from the inside once it is back in the vehicle. Planning for what will happen will save time in the end.

Reinstall the return spring. If the single ball bearing came out earlier when the contents were dumped into your hand, make sure you install it before installing the spring. Thanks to one of the readers for pointing this out.

Make sure it goes in completely.

Install the new plunger assembly.

Push it in to make sure it moves smoothly and seats completely.

Let loose of the plunger and make sure it rebounds smoothly and quickly.

Install the cover.

Slide in the cable support clip.

Install the last screw.

If you would like to test the starter, you will need a jumper wire similar to the one in the folowing picture. Using a jump pack or a set of battery cables attached to a good battery. Connect the ground cable to the case of the starter (one of the mounting ears is a good location). Attach the positive cable to the copper bolt on the starter and touch the end of the installed lead to the starter post (bolt). The drive should extend out and the starter will rotate. The starter must be held securely and safely. The starter will try to jump violently when the jumper wire is touched to the starter post (bolt). Also the gear will extend and rotate rapidly. You must have all body parts safely away from this area and do not wear loose clothing that may get caught in the gear. You will feel a lot of pain and have physical damage to your body if you get wound up in the starter drive (gear) as it is rotating.

One of the most important steps is to properly tighten the battery cable to the starter. As you tighten the cable it will try to rotate and if it does it will raise the edge of the contact inside. What I normally do is hold the cable with one hand and tighten the nut with the other. I tighten it to 15-20ft lbs and stop just as I feel a slight movement in the stud. Remember how I left one edge of the contact sitting a little high. Well, now it is level.

To order your contacts and plunger click here or visit . If you have already take your starter apart you can visually match the parts you need. If not you will need to supply the year, make, model, engine size and transmission type. Idealy the actual starter number would be best and it can be found on the side of the starter motor as seen in the picture below.

4 discussions on “Replacing The Contacts And Plunger In A Denso OSGR Starter”

  1. Found my own answer by pulling apart another identical starter I found on a friends car. The ball was 8.69mm (11/32″) dia. Many starter balls appear to be 7.07mm (9/32″) according to my local auto-electric mechanic, but mine was a less common size so I had to buy a new ball from a local bearing supplier. Just thought I would drop you an FYI in case anyone else loses their ball.

    Again, your article was great and very complete.

  2. Thanks Sparky . This makes a fantastic detailed visual reference guide for reassembling the electrical parts on a starter.

    Since it sounds like you may have disassembled a few starters in your time, do you happen to know the diameter of the single ball bearing that is in hole in the solenoid on common Nippondenso starters (a 96 Dodge Caravan to be exact)? I could not shake the ball out of the starter as you described, but after I fully disassembled the starter I managed to lose the ball so am needing to replace it.

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