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446 Engine
Posted: Mon Jan 24, 2022 3:23 pm
by Vivala446
I've got a 446 I bought back in October. Always wanted one of the high wheel tractors and finally got one. Unfortunately, I was either taken for a ride or the guy I bought it from had no idea what he was talking about. Long story short, it turned out the engine (Onan B43M) was only running on one piston as the other had thrown its rod. I pulled the engine and replaced both rods and pistons with used ones I bought online. Got it all back together and now the engine will turn all day long but will not fire. There appears to be an issue getting fuel but it will not fire even when gas or starter fluid is put directly into the carb. Plugs are sparking. I checked the heads and found what I (as a novice) would consider a lot of slop in the pistons. Got a compression tester and found that each cyllinder is registering zero. My question would be where to go now... I figure my options are to keep banging my head with this Onan in the hopes that I get it running before time to start mowing, repower it with a Vanguard and kit, or just junk the whole machine and buy something new. Any help would be appreciated.
Re: 446 Engine
Posted: Mon Jan 24, 2022 4:01 pm
by Spike188
Vivala446
page 18,
https://manuals.ccigt.com/More/Onan-BSe ... Manual.pdf
If there is no compression then you have a valve issue. Are they opening and closing? It there carbon lodged in them causing them to stick or not close properly? If they are opening and closing completely then is the valve timing correct.
Those are questions to start with.
Spike188
Re: 446 Engine
Posted: Mon Jan 24, 2022 4:30 pm
by Vivala446
I checked the valves when I had the heads off. Everything looked good to me. Seated properly and opening and closing good.
I'm no certified mechanic but I feel that the rings are not sealing things up good enough. But I'll admit that I could be 100 percent wrong on that
BTW, I appreciate the quick response.
Re: 446 Engine
Posted: Mon Jan 24, 2022 4:37 pm
by Spike188
Sometimes putting a table spoon of oil in the cylinder will bring the compression up enough to start. I have a 446 that had near zero compression and was able to bring it back to life using that method. The best compression test registered after that was 75 psi. It does need an overhaul but at least hydraulic and drive train were able to be tested.
Spike
Re: 446 Engine
Posted: Mon Jan 24, 2022 4:43 pm
by Vivala446
I'll give that a try.
I'm assuming that if none of those things work the last option would be pulling the engine again and re-ringing it.
Re: 446 Engine
Posted: Mon Jan 24, 2022 4:49 pm
by Spike188
@Vivala446 Did it start and run on one cylinder?
Spike
Re: 446 Engine
Posted: Mon Jan 24, 2022 5:01 pm
by Eugen
Zero compression would mean there are actual holes by the rings. I suspect the engine timing is way off. If the valves don't close when they should it's impossible to build any pressure in the cylinder.
You should be able to assess this even just with the heads off, turning the engine and paying attention to the valves and piston.
Re: 446 Engine
Posted: Mon Jan 24, 2022 5:12 pm
by propane1
My guess is that valve timing is off, but it did run on one cylinder when you got it. But if you did not touch any of that part, it should be the same.
Another guess is that you put pistons in this engine, and say they seem sloppy. So maybe the engine is bored out 0.030 and you put standard pistons in.
Noel
Re: 446 Engine
Posted: Mon Jan 24, 2022 5:21 pm
by Eugen
Good point Noel! The pistons must be stamped with their size, std for standard, 010 or 020 or 030.
Did you take any pictures of any of the pistons, old and new old?
Re: 446 Engine
Posted: Mon Jan 24, 2022 5:28 pm
by DavidBarkey
Vivala446 wrote: ↑Mon Jan 24, 2022 3:23 pm
I've got a 446 I bought back in October. Always wanted one of the high wheel tractors and finally got one. Unfortunately, I was either taken for a ride or the guy I bought it from had no idea what he was talking about. Long story short, it turned out the engine (Onan B43M) was only running on one piston as the other had thrown its rod. I pulled the engine and replaced both rods and pistons with used ones I bought online. Got it all back together and now the engine will turn all day long but will not fire. There appears to be an issue getting fuel but it will not fire even when gas or starter fluid is put directly into the carb. Plugs are sparking. I checked the heads and found what I (as a novice) would consider a lot of slop in the pistons. Got a compression tester and found that each cyllinder is registering zero. My question would be where to go now... I figure my options are to keep banging my head with this Onan in the hopes that I get it running before time to start mowing, repower it with a Vanguard and kit, or just junk the whole machine and buy something new. Any help would be appreciated.
Welcome aboard
Did you have the cam or crank out of the engine ?
Did you adjust the valve clearance ? No valve clearance, can cause no compression.
What rings did you use the ones that came out of each cylinder or the one on the used pistons ?
Who"s gaskets did you use .
Was there anything stamped on the top of the old pistons and the new used pistons ?
What shape was the crank in ?
Did the pistons come all the way out to the end of the block when at top dead centre ? A lot of the onans have the same diameter pistons in the same block , but have different stroke and that changes the rod length . The wrong rod , too short would cause no compression.
Bear with us we will help you figure it out .
Dave