LT40 Rescue

Brob1969 · March 08, 2021, 07:51:41 AM

Pulled the heads today. All 4 valves were in the closed position and the pistons were both mid-stroke. The cylinders were clean and appear to be in good shape. The piston faces and heads had a good bit of soot on them. Maybe it was running too rich?

The exhaust valves operate smoothly and the seats look good.
The intake valves are basically stuck. I managed to coax them open, but they are far too tight for the return spring to close. I have them soaking in penetrating oil, but I went ahead and ordered new valves as I believe I will ultimately have to pull these valves in a manner that will render them useless.

All in all, the engine looks in good condition aside from the stuck intake valves. I intend to get this 18 HP Briggs back up and running, but an upgrade I still on the table.

terrifictimbersllc · March 08, 2021, 08:01:34 AM

Looks like you are the right guy for this rescue.

Brob1969 · March 08, 2021, 11:43:32 AM

Thanks for the vote of confidence Terrific Timbers! I sure hope so. I was hoping to possibly test out the mill on a log this past weekend, but alas the carpenter ants had a different path chosen for me.
The upside is I will know the valves are properly seated and adjusted. The engine does appear to have low hours so hopefully I'll get some service out of it.

Brob1969 · March 09, 2021, 10:18:17 PM

So my new intake valves came in early enough today that I was able to pick them up on the way to my jobsite; meaning that I would have them in time to get a little work in on the sawmill engine before dark when I got home.

I set about removing the existing valves that I'd been soaking in penetrating oil; I have to say of all the engines I've ever worked on, be they a small engine or on a piece of heavy equipment, these valves were stuck more than any other I've worked on. That ant colony didn't do the valve any favors. I'm assuming that there was a chemical reaction to the "ant juice" that got in between the valve and the sleeve. Ended up taking a pipe wrench 🔧 to the valve and prying against the stem from the other end. Then once the valve stem was flush with the sleeve, I grabbed the valve with a pair of VERY tight vice grips and twisted and pulled for quite some time before I finally got the valve out! Both sides were equally as difficult! Interestingly both exhaust valves moved freely and seal tightly.
I checked both valve sleeves, lubed them up, and easily slid the new valves in. They feel good in the sleeves. I plan to get up early enough tomorrow to lap in the valves. Hopefully I'll be able to get it together tomorrow evening after work.

donbj · March 10, 2021, 03:00:18 AM

Enjoying watching this progress. I hope the engine works out. I would be going the same route. Fingers crossed!

farmfromkansas · March 10, 2021, 08:55:26 AM

How did the valve seats look after you removed the valves?

Brob1969 · March 10, 2021, 09:50:22 AM

The valve seats look fine. I will lap them in before I put the springs back to be sure they are seating properly.

I did uncover a hole in the intake chamber of one of the cylinders. It was likely a result of the corrosion caused by the ants. This evening I am going to attempt to braze the area.

Bandmill Bandit · March 10, 2021, 12:24:36 PM

If I was grading your progress in shop class you'd have an A+ so far! your doing a great job! Keep it up. It is looking real good.

That little hole is likely going to be a debilitating problem. Brazing cast is not a simple task. Depending where it is, high temp JB weld may be a better fix and it will be a temp fix. Brazing will likely leave you with hair line cracks UNLESS you can pre heat the block to an acceptable cast welding temp and then you need a good controlled cooling facility and if it is aluminum it wont braze at all.

donbj · March 10, 2021, 01:07:28 PM

I wonder if tig may be the way to go. But that may be a pricey option if you don't have one.

Maine Miller · March 10, 2021, 03:13:25 PM

Nice progress on the rebuild so far. As others have mentioned, that hole may be hard to repair for the long term. Another option may be to replace that jug with another one. A quick search on eBay turned up a few for cheap money, used and new.

Brob1969 · March 10, 2021, 07:56:59 PM

I cleaned up the area really well prior to working on it this evening. I don't currently own a TIG welder, but I have in the past used my MIG to weld aluminum successfully. Given the tight space and type of repair, that was definitely not an option in this case.
I wasn't too enamored with the prospect of using high-temp JB Weld this close to the combustion chamber. Having used the Hobart aluminum brazing rods previously with some success, I thought it was worth a shot given I've come this far.

I couldn't get the area hot enough using MAPP gas, so I set the MAPP torch up where it was blasting down into the intake chamber from the manifold port and pulled out the oxy-acetylene torch and concentrated that heat on the hole. I got the area hot enough to get the rod to flow, it ran down through the hole and puddled up on the outside of the cylinder wall forming a pool all the way to the inside of the intake chamber, where it pooled up behind the valve seat. I shaped it a bit with the dremel to clean it up some, but man is that stuff hard! I'm not going to be using this engine for high performance racing, so I don't think any changes in airflow will be a problem.

After making the repair, I ground the valve stem to the proper clearance, then lapped it in well. After I felt it was properly seated, I poured the chamber full of SeaFoam to see if it leaked anywhere. So far it's been about an hour and it's still full so here's to hoping the repair holds!

Maine Miller, I wish I could replace the jug on this engine, however they're cast as one piece with the block. This is basically my last ditch effort to save this engine. If this doesn't hold up, I will be looking to swap the engine with a 23 HP RATO engine.

DennisK · March 10, 2021, 08:06:37 PM

Pre heat it good and stick weld with nickel alloy rod.

Ooops, you were posting as I was, disregard.

donbj · March 10, 2021, 09:50:08 PM

Nice work. Got my fingers crossed for you! Right up my alley trying to save that thing. I hope it holds.

Bandmill Bandit · March 11, 2021, 02:05:33 PM

IF you get a year out of it you'll have earned the money to replace the motor. Looks to me like it should work for awhile. BUT don't go cheap on a new motor and get up around 30HP or better. the price difference for the power is well worth it. The improved torque on an overhead valve engine is noticeable and fuel injected runs better with less headaches.

Brob1969 · March 11, 2021, 09:33:40 PM

Bandit, that was along my line of thinking as well regarding getting some life out of this engine.

I was thinking the 25 HP range, but I haven't been running this mill yet. I appreciate any input from anyone sawing for awhile. You have me looking into a little more power now.

Southside · March 11, 2021, 10:51:10 PM

In the sawmill world a power plant that does not have spark plugs is king, either of the two options.

Andries · March 12, 2021, 05:26:45 AM

The old LT40 was designed for a specific weight range for the power plant.
A 25 hp Kohler, a 38 hp Kohler and a Yanmar diesel are very different in what they weigh.
Sure, more torque is better. No question.
What can the rest of the mill handle up there, and still be able to move?
A Woodmizer techie would be able to answer that.

Brob1969 · March 12, 2021, 09:56:32 PM

I had enough time this evening to lap in all the valves; both the new intake valves as well as the existing exhaust valves.
This engine was barely broken in, the factory crosshatching in the cylinders is still clearly visible, and the valve seats cleaned up nicely and well within spec. This is why I hope the repair holds for awhile. Believe me though, I've been looking at upgrading powerplants should it come to that; who wouldn't want a little more HP, right?

That said, I'm thinking tomorrow is going to be the moment of truth. I have everything ready to go back together, I cleaned everything pretty well and I will do the final tidying in the morning and then re-install the valve springs and set up to put the heads and intake back on the block.

I'll probably go ahead and pull the flywheel tomorrow as I'm pretty sure there is a mouse nest underneath. A small field mouse came out from under the other day and scampered off! I managed to get a video of the little thing as it leapt from the mill. I'm hoping the stator is all unscathed.

Southside · March 12, 2021, 11:25:13 PM

Gotta have video of the launch!!

Bandmill Bandit · March 13, 2021, 10:06:02 AM

Quote from: Southside on March 11, 2021, 10:51:10 PM
In the sawmill world a power plant that does not have spark plugs is king, either of the two options.

Southside;
I get the reality of your comment re Plugs versus injectors BUT there are situations where a diesel is not particularly practical. Thats where I am ay the moment. Gas is a simpler method for me as I don't need storage for 2 different fuels every where I go with the mill.
Also when you look at the torque specs of the top rated V-twin air cooled and water cooled fuel injected gas engines the difference to a similar size diesel is not that great. My Kohler sips fuel for its power rating and it is not stock. I did some performance enhancement polishing/trimming to the heads and intake parts and the ECM is not stock. Dyno test has it at about 34HP with a real good torque rise and gentle hold curve at the top of the rise zone. I could get another 4 or 5 HP but i am happy with it the way it is.
There are mod parts available in Germany as it is a popular ultralight aircraft engine. Apparently there are guys running the 745s up to 50 plus HP in that application but I have yet to find one to talk to.

Southside · March 13, 2021, 12:59:49 PM

Well I was also inferring to plugs vs magnetic starters.... ;D. Didn't realize you could mod the small engines to that degree and keep them alive. What was the factory HP rating? Are those expensive mods?

Bandmill Bandit · March 13, 2021, 02:56:00 PM

The head re work is mostly labor if you get it done by a pro. I had my done by a life long friend that has/runs an engine rebuild machine shop that needed a whack of logs milled so we did some horse tradin. He valued the work and parts at $200 for both heads.

The ECM mods are a result of a cousin that worked in the upper management of Kohler engine R&D untill he retired a year ago. He sent me a thumb drive and and a cable to connect a laptop to the engine and do a "software update". I have no idea what that is worth as it cost me nothing and I have not checked if it is something you can get as an after market product. I assume that it is as the light aviation guys over there seem to be getting some how.

Brob1969 · March 14, 2021, 08:17:38 AM

I had the opportunity to work on the engine yesterday. I removed the flywheel and I am glad I did. It was a pain to remove the flywheel, even with a puller. I broke one of the puller bolts on the first attempt and had to run into town for a replacement. The stator definitely needed a good sanding, and one of the magnets had come loose from the flywheel. I mixed up some west system epoxy with colloidal silica for a good adhesive and reset the magnet.

I managed to get everything back together on the engine with the exception of the cooling shroud as I ended up helping a friend load a big trailer with my skid-steer. It took a 2 hour chunk out of the middle of the afternoon, so I really didn't have time to do the final connections and get the chance to start it. Interestingly the full gasket set I bought for the engine was not a full gasket set as it did not contain the 3 valve cover gaskets so I had to use silicone. Not a huge deal other than it not being a true full set of gaskets as advertised.