Honda 350 Starter Motor Rebuild & the Mystery of the Missing O-Ring

[fxray]

I just finished rebuilding the electric starter motor for my 1970 SL350 K0, and took some pictures along the way. It’s been 9 years since I did the one for my 1971 CL350 K3 (which still works very well), so I decided to refresh my memory before I began. I remembered that there was a good write-up by ApexSpeed on the old forum. Trouble is, all the pictures have disappeared. He is aware of that, but doesn’t know why they are gone. I don’t look for them to come back.


So, I watched some videos, which I know is frowned upon here on VHT. All three videos have one glaring error in common. As usual, the videos are useful to watch how things come apart, but maybe not so useful on how to reassemble. At least you can see all the pieces and make your own decisions, right? All three videos featured the use of a purchased rebuild kit. The kits were all short one major O-ring, which led to the video people being perplexed when they put their starters back together.


Here are links to the videos I watched:


Saturday Wrench did a pretty good job till 23:10, where the missing O-ring showed up, or, more correctly, failed to show up. Also, he had some parts left over from his kit, such as the ball bearing and lip seal, which he really should have installed, but he wasn’t sure how to change them out.


https://youtu.be/IELZjICbtHg?t=16


Over in England, we have Henrietta the Honda, whose owner made a pretty good video on starter rebuild, up until 14:45 where the missing O-ring tripped him up a bit:


https://youtu.be/MTY4oQn_jdA


Finally, our "heroes" at Common Motor Collective did a nice job until 9:58, where they installed the wrong gasket first. But it’s O.K. because, after they grabbed the splines on the starter shaft with a pair of channel lock pliers and yanked it back and forth to check end play of the armature, they decided to remove that wrong gasket and not use any gaskets at all! They sell the starter rebuild kit that they demonstrated in the video, but it is also missing the major O-ring:


https://youtu.be/lEORB5igprw


You may wonder why I think there was an O-ring missing from the kits in all three videos. I got my first clue from checking the Honda Parts manual that calls for:


2 (two) item #9, 31206-402-008 O-ring (60mm x 1.4mm)
​
Then I checked CMSNL, who also call for two of those O-rings, by the same part number but they are item #16 on their fiche. They have them in stock at €7.50 each. Their exploded view diagram shows where both O-rings are located:
Honda SL350 MOTOSPORT 1969 K0 USA ALTERNATOR / STARTER MOTOR - buy ALTERNATOR / STARTER MOTOR spares online (cmsnl.com)


Same at Partzilla, where the O-ring is pictured and they call out two of them, but show it as unavailable. No problem though, because David Silver Spares has some in their UK Warehouse for only $10.38 each:
David Silver Spares USA - 31206-402-008


As an alternative, I bought mine at McMaster-Carr, opting for Viton, and buying the minimum quantity of 5 pieces for $7.40 (plus shipping of course):
https://www.mcmaster.com/1295N196

That said, how about some pictures? Here you go.


My starter came to me in pieces as part of a basket case. The nose cone was still stuck into the upper crankcase on the engine, but the other pieces were in a plastic bag along with several extraneous pieces that were not part of the starter.





I won’t make this a step-by-step instructional on starter rebuild. For that, I recommend the videos that I linked, except for the faults that I listed – especially the missing O-ring. I also recommend buying the kit if you can find one. I only bought the pieces I thought I needed. It would have been cheaper to buy a kit and throw away the stuff I didn’t need. Oh well! Here are some pictures.

Bolts as found:





Nose cone removed from the upper crankcase and disassembled:

















Alignment marks – there are more on the other end as well.





Cap off the brush end, full of carbon dust, which is to be expected.








One of the two large O-rings. My other one was missing because the starter came to me in pieces.

 

[fxray]

(Continued from above)


Removing the felt seal from under the bushing. That is in there to be soaked with oil and then release it to the bushing over the lifetime of the starter motor. This was not mentioned in the videos.







The single screw and washer to remove the positive lead from the brush. With this off, the brush plate can be removed.









My starter had two shims on the brush end, .008” (.20mm) thickness on each.











Brushes need 5mm minimum length to be serviceable. Mine were 11mm.





Now to look at the drive end, which was already apart on my starter.

 

[fxray]

(Continued from above)

Shims on this end also:



The armature can slide out this end, but not from the other. There has been some confusion on this from another old video on the internet.



Guts out, I put my empty case back together, added some duct tape over the opening on the drive end, degreased it and glass blasted it to bare metal. Then I wiped it down with alcohol and sprayed it with 3 coats of Duplicolor DE12 primer and 3 more of DE1615 Engine Paint – Excellent product!



The armature wasn’t bad and just needed a light cleanup.





The stack-up of washers and nuts on the starter motor positive (+) terminal. This is the end where the long cable from the starter solenoid, which is located up near the battery, connects to the starter motor. The motor grounds through the mounting pads, which need to be free of paint.



The brush plate after flushing with some CRC Contact cleaner.





Armature back in the painted housing. One of the 60x1.4 O-rings goes onto the shiny, bare metal part of the housing before the end cap goes back on.



Looking closely you can see the O-ring here. My brush plate got tilted while I was taking the picture, but it sat right back down.



These are the mounting pads that need to be free of paint and shiny for good electrical ground connection. Same goes for the mating pads on the engine’s upper crankcase.

 

[fxray]

(Continued from above)


A pair of homemade gaskets, 1.10mm (.043”) thick on the left, and .18mm (.007”) on the right (cut from a piece of white cardstock that was still in my gasket storage from when I made the one for my CL350 back 9 years ago). Note that my gasket material for the thicker gasket is .10 mm thicker than the nominal 1.00mm, but it will compress and is close enough anyhow.





If you buy the kit, you will get a new sintered bronze bushing. I didn’t buy the kit, so I tapped the old one out (a light press fit) from the plate. That let me blast the plate and plate it with zinc – not to make it pretty, but to prevent rust.





Then I soaked the bushing in light oil and tapped it back in. The Common Motor guy says to smear it with some grease, but in the past I have read in a number of places that it was a bad idea to use grease of any kind on the sintered bronze bushings. The thought is that the grease would plug the pores. So, I soaked the original bushing in motor oil and reused it.





The felt ring in the brush end cap is sort of like the felt on a breaker points cam, set up to act as a reservoir for additional oil. I soaked it with oil and put it back in.





I put the original shims back in, with a light smear of oil.








Now it is time to think about the other 60x1.4mm O-ring that was missing in action in all the videos I watched. I actually used 60x1.5 Viton O-rings from McMaster-Carr, because that is the closest they had and is very much close enough.


The depth of the counterbore on the drive end of the starter’s center case is 4.50mm.





The first gasket to go in is 1.00mm thick.





My home-made gasket may not be pretty but is effective. With this gasket installed, we have 4.50 – 1.10 = 3.40mm depth remaining in the counterbore.





I reused the original shim stack on this end also, again lightly smeared with oil.

 

[fxray]

Next comes the plate that holds the bronze bushing. It is 2.00mm thick.







There is still a bit of a recess in the counterbore 4.50 - 1.10 - 2.00 = 1.4mm





In goes the thinner gasket on the top of the plate. Note that it is narrower than the black gasket. That is to allow clearance for the spinning planet gears that are about to go in there. This gasket is .10mm thick, so our remaining counterbore depth is now:

4.50 - 1.10 - 2.00 - .10 = 1.30mm



Now let’s measure the protrusion on the mating part – the starter nose cone.





It is 2.20mm. But wait! I just said there was only 1.30mm of counterbore remaining. How will this work out? The answer is that there will be a gap when the nose cone is assembled to the main body of the starter. The gap will be:

2.20 - 1.30 = .90mm

This gap is just perfect for the missing 60x1.5 O-ring to be installed and slightly compressed, which is what Honda intended in the first place! None of the video guys installed it though. They voiced some concern about the gap, but decided that it would close eventually as the gaskets compressed over time. I used the O-ring, as called out in the Honda Parts Manual, and found it to be a perfect fit.

Here you can see the black O-ring on the body of the nose cone, and some white lithium grease on the planetary gears. Some recommend using heavy red axle grease, but I fear that would not work so well in the cold. In any case, I used white lithium from the same tube way back when I rebuilt my CL350 starter and it still works great.



I used my long bolts to hold the starter together while I was blasting and painting it. When the paint was dry, I removed the bolts to blast them bare and plate them with some zinc:

 

[fxray]

(continued from above)

All back together as it once was, years ago. Note the alignment marks and the bare mounting pads.



My 60x1.5mm O-ring is silver because it was on the carcass when I painted it.





One piece is still missing – the O-ring for the nose cone. This is critical or there will be a major oil leak where the starter fits into the upper crankcase. I suspect my starter needed the seal replaced at some point in the past because it was caked with oil and dirt.
I have read that some people use an O-ring from Ace Hardware. I have found that Ace sells two different O-rings with this nominal cross sectional area. One is too fat to assemble; the other is too thin to seal. I heartily recommend the original one from Honda. If the Ace one worked for you, congratulations, but I don’t care. This is one place where I believe OEM is best.





Here is a picture of the old seal and the old ball bearing that I removed from the nose cone of my starter. Note that the bearing is sealed on one side. The sealed side was toward the engine; the open side toward the starter motor. I bought a new bearing and seal from my local bearing house because I didn’t want to send away for the kit and wait for it. This was sort of stupid, because with shipping and tax, I paid even more for these two parts than the whole kit would have cost and I could have simply pitched the parts I didn’t need from the kit. The new bearing that I bought was sealed both sides, so I simply removed one of the side plates from it.





“That’s all well and good, but does it spin up? you might ask.

Well, yes, indeed it does! I keep an old 12 volt battery on the shelf for testing purposes, so I got it out and hooked up some temporary leads. Nothing. The battery showed a no-load voltage of 6.28V, which is very dead indeed. So I got out my ancient battery charger. The battery would not take a charge but the starter spun right up when tested with the charger itself.





As a final note, I took my old, dead shop battery up to the Autozone Store where I learned they give a $10.00 in-store credit for old, dead batteries such as mine. I used the credit to buy another tube of white lithium grease, since I had used the last of my ancient supply on the planetary gears in this starter.



I still have a $3.14 credit left to entice me back into their store.

So, that's my starter motor mini project. I hope someone will find it helpful!

Ray

 

[ancientdad]

Absolutely excellent Ray, nice properly-done work. It is now a sticky thread.