"Good" V4 crossflow build

[hq_]

Hi everyone,

This is my first post here, even though I've been lurking around for years and decided to register a while ago.

I found my old '89 Evinrude 90 in my basement a few weeks ago. It's been disassembled since 1990, after a piece of a piston skirt chipped off and scored one of the cylinders; at the time repairing it with OEM parts wasn't worth the cost and effort but recently I've been thinking about rebuilding it. Mostly because my teenage son is getting a bit frustrated with his 13' + 20hp aluminum boat (no waterskiing, slow) and this might be an ideal father-son -project. I have 25+ years of experience working with engines, both 4- and 2-stroke, and I'd love to pass some of this to him.

In any case, I just bought a seized '76 135hp engine for parts (carbs, heads, bubbleback) and for porting measurements. I know the crank splines don't match to those of '89 but the engine was dirt cheap and I'm not planning to use the block/crank anyway.

My idea of the build is as follows:

.030 or .040 overbore, low ring pistons for durability
Porting the 90 block to 135hp specs + using some of the tricks from "9 pages" mod list
Installing exhaust fillers and machining the surface flat for bubbleback
Machining the exhaust divider as in 140hp crossflows
"Siamesing" the 90 intake manifold
Rebuilt 135 carbs, converted from choke to primer
135 heads, of course, for compression
Intake filler blocks from 140
Composite reeds

...and lots of rejetting, trial and error (no outboard dynos around), on premium fuel only.

Is there something I have missed? The whole engine is completely apart right now so it's easy to do almost anything at this point. I have some experience of porting 4-stroke heads and 2-stroke cylinders so I'm confident that duplicating the 135 porting on 90 won't be a problem, nor will be squaring off the ports as per "9 pages".

The boat where this engine will go is still undetermined. Finnish-built Finnsport 500 (17', 550lbs bare, modified v) is a good candidate for up to 60mph or so @ expected 125-130 propshaft horsepower, but my son would prefer a slightly heavier bowrider hull. Finding a Hydrostream in Europe is extremely difficult, otherwise a Voyager or a Vamp would be ideal. I'll reckon we'll end up with a 17'-ish Fletcher, 18' Hydrolift or similar at a little over 1000lbs - is there something we should consider when building the engine for a "heavier" hull like this? Tubing and waterskiing is definitely a consideration and losing too much bottom end grunt isn't desirable, even though a lot can be done with prop selection.

All ideas and advice are much appreciated. This is the first complete outboard engine rebuild I'll attempt and I want to do it right.

[evilrude 1]

From the sounds of it you seem to have a good idea of what you want and I feel you are on the right track to a nice motor.
You could also machine the transfer ports down quite a bit(where the covers bolt to) to aid in velocity. the intake and front block half can also be milled down again to increase crank case compression.
Finger porting is also an option--not so much for power but for the cooling effect and the reliability factor.

I am also doing the same to a 83 140 but sadly I have run out of steam and its just collecting dust in my shop---one day though !

[racer]

Sounds good except for the intake mod, I would just clean it up as over all it will be a much smoother running engine and easier to jet. Dont go too square on the ports for every day type use.

[hq_]

Thanks, evilrude 1 & racer.

I've thought about finger porting but when done properly, cost vs. benefit is slightly questionable. One school of thought thinks they're not really necessary so I'm undecided. Having a machine shop do it will set me back at least €100/cyl. With a looper I'd do it in a heartbeat, but in this case... not sure.

As far as machining the transfer ports (and piston skirts) is concerned, that's one of the "9 pages" tricks I'm about to use. Machining the front of the block is new to me, I assume this means machining the surface reed blocks seal against?

How much modifying the intake actually affects the smoothness of the engine? I mean, this won't be a trolling motor and the only time it'll be on gear at idle is when docking and maneuvering into position to pull a skier up. I thought I'd probably use a ½" or even slightly larger cutter for squaring the ports and chamfer the edges fairly liberally. I'm not sure how these engines react to chamfering the edges of piston rings very, very slightly. It has a tendency to improve reliability with squared ports but with some engine designs it can cause some loss of compression.

Finding a compromise is sometimes difficult. All in all I'd like to build a durable lake motor that will last at least a few hundred hours of (knowing how teenagers are, possibly hard) use with normal maintenance, but at the same time extract as much usable power as possible - and have my son learn some tricks of the trade while building it. What I don't want to hear is that I forgot or missed a couple of easy, effective power increasing mods when all is said and done and the engine is back together and running again.

[evilrude 1]

By maching the front half of the block I was refering to where the intake bolts on to--not where the reed blocks screw on too. I have milled off most if not all the recirculating pasages on a few that I've built with no ill effects or jeting issues. I also remove the recirculating check valves and plug them with 1/16 npt plugs.

I find that when everything is port matched and all rough edges cleaned up and properly jetted these engines (and the c/f v6)will even sound different that a stock engine and run extreamly smooth.
For a every day motor use a 5/8 cutter.

The last 235 I built ran for 5 years before I sold it.

[930turbo]

I have a nine pages V4. It runs great so far. Not much time on it yet but it acts like a stocker, only faster.

[930turbo]

I used a 1/4" cutter on my first block and a 3/8" on the second. The 1/4 block had a failure that was not port related. It is going back together very soon.

[hq_]

Thanks again, evilrude 1. A very thorough clean-up job to all ports and passages is in order, as well as port matching everything. I'm not sure whether to sandblast all ported surfaces to finish them up. It may prevent fuel droplets condensing on smooth surfaces but cleaning up the block afterwards to make sure there's not a single grain of sand lodged anywhere is a lot of work.

930turbo: Interesting... I'd love to wait a bit and use your experiences with 1/4...3/8" squared ports as a guinea pig, but no two engines are the same and I'll probably go conservative with 5/8". Stocker behavior combined with more power sounds pretty much exactly what I'm looking for.

I have yet to take the 135 apart and see how much transfer ports differ from the 90, but there's one thing I've been wondering: the angle they should be ported to. Factory may have been forced to consider cost and machined them open with a straight cutter, but would you think there's benefit in porting them to a smooth radius and a slight upward angle? The piston crown is already shaped to direct gas flow upwards, and with factory design the transfer flow makes a sharp "S"-turn. As the 90 block has plenty of excess material on top of the ports, there's a chance to experiment with the angle. Unless someone already has? There's little point in re-inventing the wheel so I'll have to ask.

[930turbo]

I've always avoided angling ports on cross flow designs. This method fills the cylinder from the intake to the exhaust side. I did not want to send any intake charge over the deflector that could possibly short cut it's way out the exhaust or cause turbulence to the intended transfer path which is straight to the top once inside the cylinder.

[hq_]

Thanks 930turbo, that made the point clear. Most cylinders I've ported so far have been more or less Schneurle (loop charge) -principle engines that have a tendency to benefit from angled ports. How about slight reshaping or polishing the piston crown, then? Is there anything to be gained? A bit more mundane question would be about service parts that should be replaced while rebuilding the engine. All gaskets, bearings, thermostat and impeller are obvious, but is there something else I should remember while I'm at it?

This may shock some people, but I'm planning to keep (or re-install, more like it) VRO. There are practical reasons to it, as well as '89 already having the oil pressure (flow?) alarm, and I'll service the fuel pump after every season anyway so there seems to be little chance of a catastrophic failure. I know the bad rep earlier VRO pumps have, but also many being blamed for seized engines when the real cause has been elsewhere.

This might be a project worth documenting, providing that I remember to keep a camera in the garage every time we work on it.

Additionally, I think we may have found a boat for the engine, a mid 90's Fletcher 170 GTO. It still depends a lot on transportation costs but as a boat it's just about ideal. 1100lbs + engine, 24° V-bottom, rated for engines up to 150hp and it should be mild-mannered enough for an inexperienced driver.

[racer]

Power difference below a 1/2 inch cutter is non existent. I have run multiple combinations, 1/2 for all out power 5/8 lives better unless you run a big chamfer which hurts bottom end.

[hq_]

Damn... I just wrote half a page and my browser lost it. So let's try again.

First of all, thanks. Again.

Second, I took a good look at the ports on the 90 block and they look very similar to those of the 135. It looks like factory used the same cutter for machining them both. Is this normal? Does anyone have 135/140 port measurements at hand, just to make sure I'll have the right dimensions? I have the 90 at home and 135 is stored elsewhere (before I have time to make some room in garage) so I can't do side by side comparisons yet.

Another thing is exhaust tuner. It seems that 135 has a 'small' tuner, 140 'large' one. Is there a performance difference and should I (or could I) port the tuner to 140 specs? I'm going to port match and polish it anyway, so a little machine work won't be a problem.

Once we've done rebuilding the engine and it runs, we're not planning to take it apart again so we want to do everything right the first time. This is not an all-out race engine but if there's something I should change in specification or parts, at this point it's still very easy...

[930turbo]

If your 90 is a later model it probably has the same port holes. The 115 became the 90 when Yamaha began advertising PS HP. The 115 has the same ports as the 140. I used a 1/4 cutter on the transfer ports since they do not see the extreme heat of the exhaust. I believe this to be one of the greatest improvements because the transfer holes are not completely uncovered at BDC and this appears to increase the window area significantly. I only squared the top so they are D shaped now. No need to do the bottom. Your comment regarding the tuner, are you referring to the tuner in the adapter Plate and downhousing or the filler blocks and exhaust covers?

[930turbo]

I just read your comment about the VRO so yours is a later model. Mine is an antique '78.

[hq_]

If I've understood correctly, around 1985 when rating was changed from crankshaft to propshaft horsepower, the model designations changed approximately like...

140 -> 115/110
115 -> 90/88
90 -> discontinued

...with 'new' 115 having the same block and port timing as former 140, with lower compression heads and introduction of first generation VRO, whereas 90 inherited more conservative port timing and flat back exhaust of former 115?

I know there are special models like GT/XP100, which combines 140/115 block with flat back exhaust, but I'm still a bit confused about what's going on with my 90. Or more like, why does it already look so similar to the old (which, by the way, turned out to be '74 and not '76) 135. I'll take some photos and measurements for comparison today.

I've read some encouraging comments about 'D'-shaping the ports, I really have to look into that. Not squaring the bottoms will definitely make it easier for the rings.