Impeller housing bolts

[MostlyHrmlss]

I have a 78 Chrysler 85hp. I went to replace the impeller and managed to snap one of the housing bolts (the one that travels through the water passage, of course). I took it to a machine shop to get it taken care of. When I get it back, what do y'all think about replacing that screw with a stud and holding the housing down with a nut instead? I can't think of a reason it wouldn't work, but then again, I don't have a vivid imagination. I could maybe even go crazy and replace all four. Your thoughts?

 

[Frank Acampora]

Re: Impeller housing bolts

Bad idea.

While later Force engines did have four studs, they also had a plastic pump. With the aluminum pump, you will get corrosion that will weld the pump to the studs and you will never get it off. On your lower unit it is way better to coat the bolts with generous amounts of anti-seize and loosen them every year.

And before you ask, NO, the plastic pump will NOT fit on your lower unit. It will not fit on late Chrysler and early Force engines either.

 

[MostlyHrmlss]

Re: Impeller housing bolts

I read in another one of your postings about avoiding copper-bearing anti-seize compounds for galvanic reasons. I can't say what's in it, but this can of Fel-Pro anti-seize I bought about twenty years ago looks suspiciously like copper dust in a grease carrier. Have you found the perfect compund yet?

 

[MostlyHrmlss]

Re: Impeller housing bolts

How about having the shop tap out a bigger hole so I can use a thicker screw which would be less prone to breakage? I know, this bolt goes through the water passage and a thicker screw would reduce water flow, but I feel like the difference would be minimal.

 

[hawkf250]

Re: Impeller housing bolts

How about having the shop tap out a bigger hole so I can use a thicker screw which would be less prone to breakage? I know, this bolt goes through the water passage and a thicker screw would reduce water flow, but I feel like the difference would be minimal.

Honestly, if you follow Franks directions, you can't go wrong, oversizing the hole should be a last resort, and can cause other major problems. if you grease your bolts up well before reinstalling them, and change your impeller every year (highly recomended on those motors) you wont have a stuck bolt problem. Just be sure to grease EVERY bolt well, including the bolts that hold you lower to the mid section. Awlays fulsh your motor thoroughly with fresh water EVERY time you use it and be sure to rinse the lower cowling, midsection and transom bracket EVERY time.

 

[my1stboat1]

Re: Impeller housing bolts

all 4 of mine pulled the threads right out of the lower unit... I drilled and heli coiled the holes with replacement 1/4x20 stainless helicoils and locktighted them in... worked out well...

 

[MostlyHrmlss]

Re: Impeller housing bolts

Sounds like a plan. I'm all for taking expert advice, and from what I've been reading, one would be hard pressed to find a better expert than Frank. I just like to toss out ideas to see if perhaps I could improve on the no-win scenario of using metal hardware in a corrosive environment.

Now: let's assume that the machine shop has to drill and tap the hole anyway. Would the best plan be 1) keep it the original size (if they can), 2) oversize, or 3) put in a helicoil to restore the original threads? I noticed that I could not remove the pump plate with the broken bolt in place, so I assume that it threads through the plate and into further threads below. Will this affect the choice between 2 & 3 above?

 

[Frank Acampora]

Re: Impeller housing bolts

The holes in the stainless plate are sized to clear a 1/4 inch bolt. Yours was probably stuck from corrosion. I have had good luck with nickel based anti-seize from Locktite. I buy an 8 once plastic jar from Pep Boys for around 6 bucks. I have also seen engines that were assembled with black RTV silicone and that did seem to work well at sealing threads from corrosion. I have also heard but not seen the use of Vaseline petroleum jelly.

You do have the option of drilling the tapped holes deeper but if it is the older two piece, one bolt hole can not go too deep or it will enter the oil chamber. Heli-coils are an option but again, you still need to coat the bolt to prevent electolytic corrosion with the aluminum pump.

If yours is still the two piece that uses the pin drive prop, (I think Chrysler went to one piece in 1979) I have a couple of your lower units. Even though they look nice, they are regressive in design with a couple of major engineering flaws. Props are getting more difficult to find-- but not impossible. I have a number of three bladers, a bronze two blade, AND a couple of bronze solid hub two blade racing wheels.

But back on track-- You really should not invest a lot of money into repairs of these older lower units. For the same amount of money, you can but a newer Chrysler or Force junker engine and swap the mid and lower leg onto your engine. Everything fits. Then you have a lower unit which has a better selection of props AND is 2-3 MPH faster than the two piece.

But, you can do almost anything you want if you throw cubic money at it.

Even with a newer lower unit, At what point does it become not economical to repair. If you do the work yourself, Heli Coils will still cost upwards of 20 dollars in parts (unless you have a free source). but if you are going to invest over 100 bucks, you need to think twice as a lower unit can be had for around 300 if you search long enough. I have one or two with broken skegs and at 100 bucks a pop for a welder it is cheaper and faster to simply replace. However, my friend has just acquired a mig welder so I will learn aluminum welding. Then the repair is worth it.

 

[MostlyHrmlss]

Re: Impeller housing bolts

I already bought a 1985 parts motor for the powerhead (cracked piston in the '78). The lower unit looks absolutely identical, down to the broken pump housing bolt. If I read you correctly, this would be the better of the two? I figure it will take the same amount of effort to get the bolt out on either, so if I can manage an upgrade in the process, that's a bonus. What can I look for to tell if it is indeed the better type or an older replacement?

I was uncertain about using it since the PO put a big ol' whale tail on the cav plate, and I wasn't sure if this was a good thing. How opine thee on these fins?

 

[Frank Acampora]

Re: Impeller housing bolts

If the 85 looks exactly like your 78, then it is indeed the one piece lower unit and yes, it is the better design. Simplest for me to tell you the way to check is if the lower unit has a taper on the prop shaft and has a thrust washer behind the prop. That is a one piece lower.

Contrary to a lot of people here on the forums, I take a moderate approach to hydro-foils. They do help performance on some hulls and hinder it on others. So: It only attaches with four bolts. Try the lower unit each way and decide which gives better performance and handling. If you do not notice any difference, then run without it.

 

[MostlyHrmlss]

Re: Impeller housing bolts

Out of curiosity, just what about it is in one or two pieces? The gear housing? I had an old Johnson 40hp like that.