Evinrude Bubbleback, what is this?

[Mscanon99]

Hi All,

I have a 1994 Evinrude 115hp, I am 99% sure its a crossflow and think its a bubbleback as between the two banks of cylinders I see what looks like a bubble about the size of a softball cut in half.

I am just trying to understand this motor and learn, no problems with her, she runs great. Are all crossflows bubbleback? Whats the purpose? Lastly, if you owned one, are there any issues or special service/maintenance you would do beyond the normal?

Thanks

Best Regards,

MS

 

[reelfishin]

Re: Evinrude Bubbleback, what is this?

That bubble cover you see is the exhaust manifold cover, it and the exaust manifold are just of a protruding design which was common to earlier higher horsepower V4's. The went to that design to improve performance. I have seen a few older lower hp motors modified with that style exhaust manifold and cover too.

 

[Chinewalker]

Re: Evinrude Bubbleback, what is this?

The bubbleback exhaust tuner was used on the 135 and 140 horse models up to about 1984. When they re-rated all models to prop horsepower, the 140 became the 115, and a newer loop-charged V4 became the 140. So, essentially, your motor is the "old" 140. The bubble incorporates a tuned exhaust manifold that helps boost horsepower through better scavenging.

Prior to 1985, the only models to come with the bubbleback were the 135s and 140s. That didn't stop folks from adding the exhaust tuner to their 85s, 90s, 100s, etc. in an attempt to gain some extra power. Those models originally came with a flat plate between the cylinder banks, and are referred to as flat-backs.
- Scott

 

[reelfishin]

Re: Evinrude Bubbleback, what is this?

Wasn't the change in rated hp back in 1983/84?
I believe the first year for the 115 to have the bubble back exhaust was 1978?
The change in the 115's exhaust pretty much coincided with the change to mechanical shift as well?

 

[Chinewalker]

Re: Evinrude Bubbleback, what is this?

Nope. Last year for powerhead rated was 1984 on Johnrudes. 1985 was first year for prop rated.
1984 was also the last year of the crossflow 140 and flat back 115. They became 1985's 115 and 100 respectively, and that also made 1985 as the first year with the bubbleback on the 115.
Prior to that, the "old" 115 was kind of a cross between the 90 and the 140, using the 90's exhaust plate (flat) and the 140s intake and exhaust porting (larger than the 90).
- Scott

 

[reelfishin]

Re: Evinrude Bubbleback, what is this?

Does adding the bubble back make any real improvement to a lower hp engine?
I was always under the impression that there were other differences in the block too. The 1985 90 and 115 share a lot of parts, but the bubble back exhaust, block, and heads are definitely different. I've never bothered trying since I figured it would do more harm than good mixing various tuned package components.

That would also mean that there should be a major difference between a 1983 140 hp and a 1985 140 hp? I have one of each, actually three 140's here, a '77, 83, (E140TRLCTE), and a 1985 (E140TLCOS), all have perfect compression and all run as new, but seat of the pants, with the same prop on the same 18' boat, the '77 (140743S) pulls the best by far. They are all mechanical shift motors. For some reason the older motor has always been quick, and not by a little, it's noticeably from the minute you open the throttle. Its a long story of how I've had all of them on the same boat but over the last two seasons I've sort of played musical motors with two of my boats and sold the heaviest one with another motor. The later motors are all original, I've known both of them since new, but the 77 was gotten on a junk boat a few years ago. I do know that someone has changed the carbs to later model carbs with no choke and an enrichment solenoid. The rest looks untouched.

I was also told that not all blocks can accept the bubble back manifold due to porting?

 

[Chinewalker]

Re: Evinrude Bubbleback, what is this?

The 115 and 140 (c. 1984 & prior) have the same porting. The 90's are considerably smaller. A couple years back I picked up several crossflow V4s from that era and was able to really get a handle on what went where and why. Getting a 90 and 140 block side by side was rather enlightening. The ports on a 140 block are HUGE compared to the 90. I saved parts to build up a 140, and ended up using a 1988 GT100 block as my starting point. Only thing I need to do to it is to machine out a bit of the webbing between the cylinder banks to accept the inner manifold. I also have a set of the 1 5/16" carbs for it. It'll be a true Johnrude, as it has at least four source motors for the parts so far.

I've heard differing opinions on whether adding the bubbleback to the 90 was worth the effort with the smaller porting. DHadley is the expert on what works best with what...

Isn't your 1985 a looper? That would be a completely different motor...

- Scott

 

[reelfishin]

Re: Evinrude Bubbleback, what is this?

.....
I've heard differing opinions on whether adding the bubbleback to the 90 was worth the effort with the smaller porting. DHadley is the expert on what works best with what...

Isn't your 1985 a looper? That would be a completely different motor...

- Scott

The 1985 is an E90MLCOS with tilt and trim added from a dead 115 I had. Its also got its VRO bypassed. It came to me on a boat which I parted out.
I've actually got about 10 or so V4's here, anytime I find a deal or a freebie I grab it even if just for parts.
So far, only one early 115 turned out to be not fixable, but not because it wore out, the fool that had it tried to disassemble it with a hammer and vise grips and broke the block and mushroomed the crank down about an inch on top trying to get the flywheel off. I parted it out and put what survived on the shelf. The block was scrap. Its come in hand just for small parts and the lower unit was good.
The 90 I have runs strong, I'll probably put it on my one aluminum 18' Starcraft. It should be better on gas than the 1976 135 and its got the newer power tilt and trim. The older tilt and trim parts are getting hard to find and a bit pricey, the later version is pretty common. The 135 has a bad ram right now, I priced out the parts to fix it and it's cheaper to just hang another motor. I'll use the 135 on a boat in which I can reach the motor better from the inside and remove the tilt and trim kit altogether for now. I just need to find the tilt lock parts that the last owner removed when installing the t/t. I may be able to use the parts from that 115 I parted out.

The most common problem I find with any of these here being near salt water is wiring disease, just about every motor I see over around 10 years old or so has rotted wiring. I can't count how much time I've spent making up new harnesses or splicing wires. On a few, I just ordered new CDI brand harnesses.

 

[Chinewalker]

Re: Evinrude Bubbleback, what is this?

I think I've still got a few good used 1970s era wiring harnesses here if you need one - all freshwater up this way...
- Scott