# Helicoils



## BJW (Oct 1, 2007)

One of the bolts that holds the lower unit on my 175 Evinrude is stripped. Actually, it looks like the threads just corroded away. I am going to helicoil it. But, the threads on the helicoil are far fewer than the threads in the originall hole. One school of though says that since the helicoil threads are stainless rather than aluminum they should hold well. But, I would feel better if I put in more threads. Has anyone one of you ever put two helicoils in one after the other to double the number of threads? I could see that there might be a problem with the threads not lining up exactly on the two helicoils and causing problems. My plan at the moment is to just put the single helicoil in and not worry about it. Any thoughts or experience here?


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## Downtime2 (Sep 27, 2007)

We use em' regular at work on industrial engines. Do NOT use one on top another. Won't work at all. Get the right helicoil and it will have the same threads. The helicoil has to have the same anount of threads as the bolt or the bolt will not start. Careful drilling the hole out and don't missalign it. We only use regular hardened steel, no stainless....


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## nb&twil (Oct 2, 2007)

Honda tech school teaches that with any bolt, all that is needed is 4 threads. (thats why if youve ever worked ona honda, you would notice shorter bolts than normal) the idea is that a bolt has maximum grabbing ability on 4 threads - if the bolt grabs any more than that, it is fine, but not necessarry. even on wheel lugs, it has been found that 4 threads is just as strong as running a nut down with 20 or more contact threads.


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## BJW (Oct 1, 2007)

Thanks for the response guys. 

nb&twill: that explains why nobody has any helicoils in anything but that seemingly short length. I don't have them in front of me know, but seems like I counted just 5 turns. Makes sense.


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## Tuna Man (Oct 2, 2007)

> *BJW (5/22/2008)*Thanks for the response guys.
> 
> nb&twill: that explains why nobody has any helicoils in anything but that seemingly short length. I don't have them in front of me know, but seems like I counted just 5 turns. Makes sense.


EVERYTHING that I was going to give input on has been mentioned already... Yup that is why heilicoils are so short, just make sure the bolt you use doesn't bottom out before it is really tight.

Since it is the lower unit...Yes I would use stainless helicoil and stainless bolt.


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## brnbser (Oct 1, 2007)

in reading your post and the replies, it sounds like a couple of different thoughts going on.......

it sounds like you want the threads to go deeper, not necessarily more like you said or are you talking about course threads vs fine threads....

as far as stacking helicoils, yes it can be done if you absolutly have to......you have to modify the second helicoil to match the first. I've used this on a few high performance motors when I had to because ofa long head bolt. like the others stated above though, I wouldn't recommend it, it can be done, i've stacked as many as 3 coils and it will hold but the biggest problem comes when you have to disassemble the next time.....pita. I was doing it on race motors when I had to quick fix on race day and these didn't have the problems of corrosion your going to have.

as for using stainless or cold,both are going to react badly in a aluminumlower unit that is then dumped in salt water.......i would probably go with the stainless simply to slow down the corrosion some but they are both going to corrode away in an aluminum l/u in salt...


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## BJW (Oct 1, 2007)

I can see that my original explaination may have been confusing. The bolt is a 3/8 16. I have the 3/8 16 helicoil and the tap that is made for 3/8 16 helicoils. My concern was that I would only be getting about 5 threads of contact on the bolt. My initial thought was in getting more threads of contact. But now that I think about it I believe that the 5 threads of contact will be enough. There are 6 bolts holding on the lower unit. I am confident that I will be fine with just a standard helicoil installation. 

On the corrosing issue, when I do the annual water pump impeller I try to put sealant around the bolt holes to keep water away from the bolts just to keep down the corrosion and make the annual impeler change easier. The other bolt holes seem fine. Looks like I didn't do a good job sealing this one hole in the past.


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## brnbser (Oct 1, 2007)

since you already have some intrusion into the threads, it would probably be a good idea to chase all the threads and hit it with a good penetrant like PB Blaster before reassembly. since it is a wet environment bolt(like a head bolt entering a water jacket), use the sealing compound that doesn't harden, I think it's the type 2


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## sealark (Sep 27, 2007)

I have a question nothing to do with the bolts , or maybe it does. Why do you change the pump impeller every year? I have been running outboards for over 50 years and I change mine every 5 years regardless of the hours. The only reason to change earlier is if they are run aground in sand a lot or are not used muchand set in the heat and dry out. When I do change the impeller in the five year period there is very little wear on the tips but the rubber is starting to get hard from age.


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## brnbser (Oct 1, 2007)

I know most mfg on these newer engines recommend every other year or 200 hrs. At least that's what it is on the F250's that are on SET 4 Life. With it being a tournament used boat, we put 200 hrs on it between Jun and Nov last yr.


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## sealark (Sep 27, 2007)

> *brnbser (5/22/2008)*I know most mfg on these newer engines recommend every other year or 200 hrs. At least that's what it is on the F250's that are on SET 4 Life. With it being a tournament used boat, we put 200 hrs on it between Jun and Nov last yr.


Scott, now what would you expect a dealer to say when he has a $$$ in front of a statemt. Sure if you run aground a lot. I am just saying that after removing impellers with over 600 hours on them there is not much wear just small sings of rubber fatigue. In fact I just changed my 2004 175 HP Johnson after not quite 5 years ( Purchased in Oct 2003). and there was only a small amount of wear on the tips of the impellers. When changed it was pumping water and no problems. And I do use my boat on a regular basis. I don't see any difference between any lower unit in service today they all function the same and get the same amount of stress on the pump and seals.









PS. I change the seals when I change the complete water pump.


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## BLKFLYZ (Sep 30, 2007)

Sealark, one of th main reasons is the impellers are made of rubber and after a year of sitting in the impeller housing the the impeller conforms to the shape of the housing. Have you ever noticed how the fingers are rounded and the new impeller fingers are staight. If not changed they can cavitaite inside the housing make air bubbles. You want the impeller to push water not bubbles. Make sense? Also the rubber tends to dry rot and crack from heat and you could lose a few fingers . So I try to change mine every year regardless of sand, hours etc... Hope Ive explained it correct.


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## sealark (Sep 27, 2007)

> *BLKFLYZ (5/22/2008)*Sealark, one of th main reasons is the impellers are made of rubber and after a year of sitting in the impeller housing the the impeller conforms to the shape of the housing. Have you ever noticed how the fingers are rounded and the new impeller fingers are staight. If not changed they can cavitaite inside the housing make air bubbles. You want the impeller to push water not bubbles. Make sense? Also the rubber tends to dry rot and crack from heat and you could lose a few fingers . So I try to change mine every year regardless of sand, hours etc... Hope Ive explained it correct.


Maybe you didn't get the gist of my statements. I have for 50 years used my 5 year method without incident. As for the rubber forming to the shape you are correct on that point. But how does getting formed to that shape cause the impeller to cavitate? It rotates in the same direction all the time and the tips are in the same contact with the housing all the time they are rotating. And my impeller that I just last week replaced after a little less than 5 years was formed in the direction of rotation BUT was still very flexible with only a small amount of wear on the tips. Like I stated earlier if you run in sand or let the engine set for montes at a time in the hot sun and the pump dries out it should be changed more often. I very seldom run aground and I use my engine at least weekly. So if you want to spend the dollars every year and it makes you feel secure that's what counts. I am just telling you and anyone that wants to save a buck my experiences. Hell watch this year I might be saying when my impeller goes out before I expect it to go. Now why didn't I change it last year!!


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## brnbser (Oct 1, 2007)

i would venture to say that you gave your own explanation as to why you only need to change yours every 5 yrs.......you've been boating 50 yrs......best case scenario meaning you know what your doing, your run it, you rinse it and you don't run aground.

i'm sure the mfg recommendation is based on worst case scenario, new boater, forgets to rinse, runs it in the sand a few times a yr, viola....needs a new pump.

with SET 4 Life, it's still under full mfg warranty and it's one of those things.......well mr. mfg, I blew a powerhead......mr. boat owner, did you do your maint as per the book? well no....no new powerhead for you......


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## BJW (Oct 1, 2007)

Scott: Yes, I already chased the threads. When I saw the corrosion on the threads on one hole I was worried about the others and wanted to clean them up to get a good look. All I got out was bits of the RTV silicone I use to seal up the unit. I used carb cleaner to get all of that out and the threads look good on the other holes and once cleaned up the bolts are easily turned with little finger pressure. I guess my trying to seal them with silicone has worked, except for the one hole.

Sealark: I probably do change the impeller much more often than I need to. Unfortunately, my boat does end up sitting around a lot, up here especially in the winter. It usually doesn't move between October and April. SeaTow had to bring me in from the Gulf one time when an impeller that was 3 years old gave up. After that I am very cautious.I am the type guy thatkeepsa spare prop on the boat and a box full of parts and another prop in the tow vehicle, etc. I don't getenough time on the water and I don't want anything to stand in the way when I can go.


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## BJW (Oct 1, 2007)

Repairs complete. Re-assembly went smoothly. I took it out over the weekend, works great. Thanks to all for the input.


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