Kawasaki 25 hp V-twin

Yeah that's very low compression. 1200 hours it's probably time for a rebuild or replace

 

Rudolph would be happy

 

Yep, 1000 hrs should be half life, but like you, I've seen small engines that are basically shot at 1000 hours. One of my employees had his kohler 25 HP on his stump grinder blow at 1600 hours. Rod broke. He bought the machine with 1400 hrs and I told him that he should start to look at replacement engine costs. He got 1.75 seasons out of it. He just spent close to 3k to put a new Kohler in it

 

Thanks! Yeah, that is my engine. Different intake setup, and different muffler, but I could easily transplant those parts. It's the same bottom end and heads, or at least compatible.

If I'd started this project knowing how far I was going to have to tear this thing down, I might've actually just pulled the trigger and bought that engine (although the Deere guys had given me the impression it could no longer be had). But now I've already got the thing totally torn down, and parts arriving today or tomorrow to put it back together. Total cost is over $1000, and I'll still have an old bottom end on this thing, but I'm hoping the work I'm doing today should carry it another 1000 hours now. Bottom end still feels tight, no slop.

Two questions:

1. New heads on the way, they come with valve guides already pressed in... but are they reamed, or do I need to buy a reamer? I've pressed in new guides plenty of times, and am used to hand-reaming them, but this is the first time I've ever bought new heads with guides pre-installed.

2. Why do you guys keep saying compression is low?!? It's way above min spec. Min spec is 57 psi for this Kawi V-twin, and I was measuring 75 to 80 psi. I don't really care if automotive engines run 120+ psi, that's irrelevant with regard to the spec for this engine, unless I'm missing something big.

 

Got an answer to question no.1: pre-installed guides to not require reaming.

 

Yes it is in spec for an engine with auto compression release, but if not for that, anything under 100 PSI (110?) will not fire, (yes I know there are exceptions) or at least be VERY difficult to start...and then have low power too.

 

Yes, of course. But I stated the 57 psi spec literally no more than three words before I stated the measured value, so I'm not sure why anyone posting would expect otherwise.

 

Yup, I saw that...that's why my initial response was worded the way it was...but I don't think you are really talking about me anyways.

 

Sorry. No, I wasn't talking about you, or really anyone specifically. Really just making sure that *I* wasn't missing something important.

 

Hey. unrelated question: I'm replacing both front and rear main crank seals, and while I should be able to press out the rear seal while I have the crank case cover off, the front is inaccessible without removing the crank.

I assume procedure for removing the old is the usual trick of drilling pilot holes in the press ring, inserting sheet metal screws, and using them to draw it out with puller or prybars? I usually use a stop collar on the drill bit, just to be sure it doesn't punch thru deep enough to hit the bearing.

 

Barring some reason not to, that's how I'd do it.

 

It turns out the outer ring of these seals is just soft aluminum sheet metal, not the steel one's I've dealt with so many times before. So, I didn't even have to worry about chips from drilling. I was able to just punch thru the outer ring with a sharp awl, run a sheet metal screw in 1 - 2 threads, and pull the seals out. Easy-peasy.

Already have the breather swapped out, and the whole bottom end back together. Even started throwing shrouds and stater back on.

Bad news: It appears the old reed valve was fine. I have no easy way to test this type (not something you can put up to your mouth and blow, given odd shape), but it's definitely not blown open. I guess I should double check it's not stuck shut, but living in oil, I doubt that's the case.

So, I'll have a nicely rebuild top end, and a new breather... but now I have no idea what was causing it to run poorly. Deere guys think it was valves or head gaskets, and while I'm not seeing that myself, maybe they're right.

I'm going to rework several connectors on the various wiring harnesses tomorrow morning, then get the engine back into the mower before assembling and installing the new heads. I might have it running as soon as tomorrow night, but Sunday seems more likely.

 

Exactly.

 

Well, it's low because you're obviously past the decompression point that was made. Also, at 1000 hrs it wasn't as healthy as it could've been.

That said, you're knee deep in it and hopefully you get it fixed to get to at least that 2000 hour mark.

 

That's how I did it on my Kohler.

 

Well, it's fixed. The problem was not the breather, or the valves, or the head gasket, or the valve guides. I mean, there were plenty of problems to go around, so it's not a bad thing I did the total tear-down and rebuild... but none of those were the problem.

I got it back together today, and the behavior was still the same. But one thing I had noticed just before all this trouble began, was that the engine RPM's were overshooting anytime the engine was unloaded. Like driving around without the PTO engaged, it would rev up when going down hills. I had assumed this was the result of whatever was causing my trouble, not actually the cause of it.

My diagnosis is: valve float.

I noticed it was idling up around 3800 RPM, and while I can't say exactly where high idle was sitting before tear-down (all the throttle linkage was moved during rebuild), the misfiring behavior was the same. I did all the adjustments for low ungoverned speed (1450 rpm), low governed speed (1550 rpm), high governed speed (3600 rpm)... and the issue went away.

The high RPM's after rebuild can be explained by the fact that I had to move and reset all the governor and throttle linkage. As to what caused the RPM's to creep up before the trouble started... I have no ideal. I can say with certainty the governor arm did not slip on its shaft, as getting that little bit of hardware apart was the source of substantial effort, a few evenings ago.

 

Oh, and one other thing I noticed: the amount of air this engine moves when it's all cleaned out, is amazing! It'll blow your shirt up when you stand behind the mower, and it's a horizontal configuration!

What's surprising is that, for an engine that's so ubiquitous among commercial zero-turn mowers, it's really an absolutely terrible design for a mower. There was grass packed in so many blind and basically totally-inaccessible air paths, that I'd guess the air flow through my engine was maybe only 20% - 30% of what it would be clean. And I'm a guy who actually blows off the engine after each use, and does the recommended maintenance of removing the three little "windows" from the blower housing to blow the thing out with compressed air on a yearly basis... as recommended.

There are two problems with the design:

1. They are known to leak, youtube is chock-full of videos of Kawi V-twins with bad breathers, bad breather gaskets, and oil leaking all over. Grass and dust sticks to this oil

2. There are a lot of blind air paths and cooling fins, which are totally inaccessible without major engine disassembly.

I've heard others mention these things, but I had no idea how bad it was, until I did a teardown of this engine myself. Easily half the total disassembly time, maybe more, was spent on cleaning.

If I ever buy another ICE-powered mower, it's probably going to be water-cooled. Of course, maybe battery mowers will be the standard, by the time I replace this thing.

 

How does the low power symptom figure in then? Valve float usually happens at very high rpm, and goes away when rpms return closer to normal...might not make for the smoothest running engine, but it'd be anything but low on power I'd think...but I've never floated valves on a vee twin mower engine though either...

 

First, there's a good chance I got this wrong, so definitely feel free to poke holes in my theory. You make a good argument there, as RPM's were dropping way, way off under load, until I adjusted all of the linkage for proper "idle" speeds (low ungoverened, low governed, high).

If the thing were getting right back up to the over-sped 3800 RPM under load, then we could blame the governor, but it wasn't... because there was no power to get there. I have no good answer for this.

But at the same time, I can't figure out what else would cause an engine to go from misbehaved when over-rev'd to normal desired behavior, with a simple 10% drop in operating RPM's.

One other thing I did notice was that the clear little inline fuel filter (you guys know the one, I must have four machines that use this same filter) has what seems to me to be very little fuel reserve in it. Like just enough to avoid sucking air at the outlet. I'm not sure if that's normal or not, never watched it that close before.