LOL !! You are obviously thinking the same as me ! Unless it had something like total lubrication failure, rod breakage, big end failure or some similar terminal failure then why would it be scrap ?
If anyone has followed this thread am I right in thinking the next step is to get the piston out and check the rings? Anything I may have missed? Or am I gona have to buy a new motor too without knowing why
It seems that I am having the opposite problem with the same L100 engine.
Too much compression.
The starter is struggling to turn the engine as it always stops just before TDC on the compression stroke (I can pull it over TDC on the pull start). After a few flicks of the key (new starter motor) it will start but when using the auto start system it keeps trying for to long before retrying so worried it will burn out (which I think is what happened to the last starter).
Is it possible to change it to the auto decompression set up?
Why would this start to happen now?
If I manually pull the engine past TDC its fine or if I manually trip the decompresser its fine.
It starts easily on one pull manually so confident that the rest of the engine is ok.
Is there actually an automatic decompresser for this engine? All I can fine is reference to the automatic resetting lever which is standard.
Suggests possibly a starter motor problem, or low power to the starter(flat or dying battery). I don't think those engines have an auto decompressor, just the manual lever; the starter is supposed to be able to cope with full compression.
If the battery is ok, check battery leads and connections. If they are ok check starter brushes. The give away for worn or faulty brushes is a hot starter motor.
Battery fully charged & showing 12.7v before starting. On activation voltage drops as expected but not like a duff battery would & recovers quickly after. Measuring at the starter gives the same results. Starter is new new not recon or used replacement. Battery leads have been changed in the last 12 months inc engine to earth link.
I get why the engine always stops at the same point due to the compression but would think that by the next start any pressure would be gone & without the full squeeze cycle peak pressure would be lower.
I wonder if they are selling starters that are for the smaller Yanmar L series engines & they cant quite cope with the L100.
Did you find the fault? I have the same engine a 4 month old yanmar l100 with both pull and electric start. Which is hard to start if I use the electric start it sounds like a flat battery, or a lazy starter. If I use the pull it really stiff to turn with compression valve down but after a turn it suddenly get easyer to turn. And after a couple of pulls it starts it will even start with electric starter. Could it be a sticking decompression valve? Help
The starter was duff, I have been through a few starters. Slightly newer engines come with better starters with more umpf (1kW instead of 0.8kW).
Mine will hand start first pull every time. If I do the following, pull slowly till its on the compression stroke, stop pulling & push the decompression lever down. Do a full length fast pull on the handle. Engine starts. Never fails.
As it happens I am working on another one at the min. I bought one as a runner with low hours & one with it as a parts supply. The runner needed a few bits fettling but is all good now. The one for parts was in good nick but would not start & had been messed with, odd bits missing & parts half removed. Been giving it a good look over. In the end I found that it has a knackered big end. So new crank & conrod with a full set of bearings & an oil pump has been ordered. Looks like I will have 3 gennies up & running soon so will have one up for sale.
Think I have similar problem to OP. I used manual decomp a day or 2 ago when battery was a bit weak - flipped the lever downwards where it stayed, and used the elec start (stephill se6000d generator). all ok, started up.. used it a bunch of times since with loads of start / stops no prob.
Then.. today, after an eventless run, i stopped it & it just wouldn't start again. Spins easy on the elec start like there's no compression. No nasty noises to indicate big broken things inside, no leaks or anything. exhaust is chuffing away so there's some kind of normal piston activity.
Going back a few days ago when I used the decomp lever - I didn't manually return it to the vertical position, I assumed it automatically clicked back up one the engine started. When I checked today, the lever was in the vertical position, but it wouldn't stay down when pressed. I'm not sure what's normal, whether it should stay down, or whether it should spring back up on finger release?
Wondering if, leaving the lever down whilst running was bad, and I should have pulled it back up again after starting, manually? Wonder if leaving it down has caused the exhaust valve to hammer the decompress mechanism to hell.
Going to go & take rocker cover off & have a look at decompression shaft, will report back. I noticed in the thread so far, nothing seems to have been directly mentioned about the actual state of the decompression shaft & it's workings inside the rocker cover?
Sorry for double post, would just edit if I could.. anyways, took the rocker cover of & all was well, shortly after though, whilst cranking fast on the elec starter, I heard something fall down inside the block & the engine just jammed solid. Must have holed the piston crown or summat. Guess I'm looking for a new generator or at least a new Yanmar L100 engine.