1956 Lark 30 vs. 1958 Big Twin 35

[Chinewalker]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

Though similar, I don't think the lower units are the same. Might be some subtle variations in the internals. Check things closely when you've got them apart before swapping things around...

 

[54fleetwin]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

Well the lower is seperated and the powerhead is NOT stuck.
The rear bearing for the propshaft is toast, everything else looks like it will clean up.
I am a little worried about drilling out the broken water pump housing bolts. They are stainless steel into alm.
Does anyone have a parts manual for the big twins?

I have the service manual but it does not show part numbers.

 

[jbjennings]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

Just wanted to say I enjoyed the pics. Those medallions are NICE!
I don't have a pdf file for the 58bigtwin part man. that I know of, but I'll look and see.
Good luck,
JBJ

 

[54fleetwin]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

thanks

 

[54fleetwin]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

Fix them both up and run twins...like this (pix).

maybe if my boat was rated for 70hp
but seeing as my boat is rated for 35 I think I will just stick with the '58 bigtwin.

JJust out of curiosty, when fitting 2 engines do you reprop for more speed?

Say I wanted to run 2 18hp engines, I would imagine 2 with the stock props would get you on plane twice as fast but I dont see how you would gain anymore speed. I think the engines would just rev out faster, so do you up the prop pitch since you have 2 engines to get to plane?

 

[54fleetwin]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

Though similar, I don't think the lower units are the same. Might be some subtle variations in the internals. Check things closely when you've got them apart before swapping things around...

This is what I have found so far comparing the '55 BT25 and '58 BT35 Lower Units
My '58 35 has rust, damage is limited to the rear propshaft bearing and lower drive shaft bearing
So far the only difference I see between the 2 lowers, is the pin that the shift bell crank rides on. On the '58 35 that pin is a screw, on the '55 25 its just a pin that sits inside the lower unit casting.
Propshafts appear to be the same, lower unit castings physically bolt up.
Rear propshaft bearing numbers are the same.
Every thing in the 25 lower unit looks good, it had what looks like black pourable grease instead of gear oil with no signs of water.


Now as for breaking the stainless screws that hold the water pump housing, I am fortuneate that only the heads broke off, I think with some time soaking with PB Blaster and a little heat I may be able to get these removed.

Shift lever is still stuck after removing lower unit, I did find a thin nut sitting in the top of the waterpump housing, at this time I suspect the nut came from the shift rod connection under the power head.
I guess the power will come off next. I suspect the other nut is jammed up there and thats what is keeping the shifter from moving.

I NEED to do the coils on this engine.

 

[54fleetwin]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

looks like I need to pull the powerhead.
Anyone have any tip on removing the pinion gear bearing and the lower drive shaft needle bearings?

 

[54fleetwin]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

Anyone have any tip on removing the pinion gear bearing and the lower drive shaft needle bearings?

bueller....bueller.....

 

[1946Zephyr]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

The pinion gear should slide right out. Just remove the two bolts that secure the drive shaft support and pull the gear out. The bearings should come out too, but the bottom bearing race will have to be pressed out. If your really good with a hammer and punch, you can drive the bearing race out.....(but I didn't tell you this)

Now that I think about it, I understand that there is a minor difference in the gears.

This link will give you an excellent parts break down on your 58 BT

http://www.marineengine.com/parts/v...evinrude-johnson/ITEM_2925/ITEM_292500001.htm

You can copy each of the pages and print these up. It'll cover every part of your motor.

 

[54fleetwin]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

The driveshaft bearing was so rusted the gear had to be driven out, the gear came out with the inside bearing race still attatched. The needle bearing doesnt look any better.

On a side note, Sierra shows a different impeller number for the '55 25 than the '58 35, however both my impeller housings have the same part number.
So which impeller do I need?

 

[samo_ott]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

I have the parts manual in pdf form if you want me to email it to you. Just PM me with your request.

 

[tmcalavy]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

I'm running stock props on both my twins, doesn't plane out any faster but does get up and go...about 5 mph faster than with a single 64 E-rude Speedifour V4 60 hp. Recently raised both motors about 2 inches on the transom and moved/plumbed the gas tank up forward under the bow skirt...need to take to the pond for a comparison splash test.

 

[1946Zephyr]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

The driveshaft bearing was so rusted the gear had to be driven out, the gear came out with the inside bearing race still attatched. The needle bearing doesnt look any better.

On a side note, Sierra shows a different impeller number for the '55 25 than the '58 35, however both my impeller housings have the same part number.
So which impeller do I need?

I would of course buy the impeller for the 58 model, unless of course if you're using the lower unit from the 25hp. Take a measurement on the driveshaft of both motors and see that they're the same size and you should be good. If the impeller housing is the same part number, then the thickness of the impeller should be the same. They may have possibly changed the drive pin for the impeller, or something, to constitute a different part number.

As far as the pinion gear goes, looks like it's best to replace it and the bearing assembly

 

[Chinewalker]

Re: 1956 Lark 30 vs. 1958 Big Twin 35

I think the only difference in the impellers is the size of the slot for the keyway. The '55 used a pin, and the '58 used a key. They widened and deepened the slot a tad to accomodate. I think you can put a '58 impeller in a '55, but not vice-versa - at least as originally designed. I'm not sure, but I think they only offer the '58 style now, which retrofits to the '55...