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Old 17-09-2019, 03:25   #1
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Angry Pre-combustion chambers

Hello,
I have a Yanmar 2QM15 engine which I'm rebuilding. The head is in good shape except that one combustion chamber seems to be partly burnt out. The hole at the entry to the cylinder has opened up to about twice the size of the other. How do I determine whether I need to replace the chamber? The cost of replacement is insane. We're talking in the range of $US320. How can this be? This is a small part maybe 45mm long .Not a complicated casting. Must be made of unobtainium. Can anyone explain how one determines whether or not replacement is necessary and secondly why the part is so furkin expensive? I actually paid less for the whole motor I'm rebuilding. I am so pissed at Yanmar and their extortionate and predatory pricing.
Cheers
Kevin
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Old 17-09-2019, 04:12   #2
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Re: Pre-combustion chambers

Quote:
Originally Posted by pullark View Post
Hello,
I have a Yanmar 2QM15 engine which I'm rebuilding. The head is in good shape except that one combustion chamber seems to be partly burnt out. The hole at the entry to the cylinder has opened up to about twice the size of the other. How do I determine whether I need to replace the chamber? The cost of replacement is insane. We're talking in the range of $US320. How can this be? This is a small part maybe 45mm long .Not a complicated casting. Must be made of unobtainium. Can anyone explain how one determines whether or not replacement is necessary and secondly why the part is so furkin expensive? I actually paid less for the whole motor I'm rebuilding. I am so pissed at Yanmar and their extortionate and predatory pricing.
Cheers
Kevin
Can you post some close up pictures of both the pre-com chambers and some measurements?

If it needs replacing, there is a reasonable chance you can find a used one somewhere! I might have a 2QM20 spare one in the shed but ATM, I don't know for sure and if it is the same or not. I'll have a look for it tomorrow and measure it.

A few of us on CF have made a mission out of finding alternatives for the excessive Yanmar pricing. Stay positive!
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Old 17-09-2019, 13:38   #3
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Re: Pre-combustion chambers

Quote:
A few of us on CF have made a mission out of finding alternatives for the excessive Yanmar pricing. Stay positive!
One alternative is spelled Kubota! So glad that I don't own a Yanmar...

Good luck with the search... both of you! Digging through Wottie's shed ain't a trivial matter...

Jim
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Old 17-09-2019, 13:51   #4
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Re: Pre-combustion chambers

That hole may be the reason that engine was so cheap.

That cylinder may not have been working very well. That hole is made a specific size for the engine, to regulate the speed at which the "fire" expands into the cylinder.

There'll be specs in the manual, but I'd say if it's twice the size, replace it.

If you're going through the trouble of rebuilding the engine, you'd hate to have a smoky one when you're done.

A used part would do the trick, but, new or used, I'd definitely replace it.

Cheers.
Paul.
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Old 17-09-2019, 16:32   #5
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Re: Pre-combustion chambers

Quote:
Originally Posted by pullark View Post
Hello,
I have a Yanmar 2QM15 engine which I'm rebuilding. The head is in good shape except that one combustion chamber seems to be partly burnt out. The hole at the entry to the cylinder has opened up to about twice the size of the other. How do I determine whether I need to replace the chamber? The cost of replacement is insane. We're talking in the range of $US320. How can this be? This is a small part maybe 45mm long .Not a complicated casting. Must be made of unobtainium. Can anyone explain how one determines whether or not replacement is necessary and secondly why the part is so furkin expensive? I actually paid less for the whole motor I'm rebuilding. I am so pissed at Yanmar and their extortionate and predatory pricing.
Cheers
Kevin
Sadly you've fallen into the clutches of the Yanmar mafia. I'll tell you how it can be, it's that some people pay them so the extortion racket goes on.
Where on the planet are you? I can help with some parts but not the pre-com chamber. My tip is to take the chamber to a tractor place ( Some John Deere stuff uses Yanmar engines AFAIK) & see if they have one. The pre-com chamber will be used in many different models.
It depends on the parts guy wether they'll help you out.
I'm not sure how critical the pre-com is but one on my customers had his cylinder head planed ( against my advice ) & the machinist cut into the pre-com chamber & it had a big hole in it but the engine still ran ok. This was a YSE8 which is basically 1/2 of a 2QM15
You can PM me if you want aftermarket parts
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Old 17-09-2019, 17:46   #6
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Pre-combustion chambers

Just about all the smaller John Deereís are Yanmarís they donít try to disguise it.
My gas motor JD 425 was a Kawasaki, John Deereís use of Japanese engines goes way back.
Your problem may be cross matching the part numbers though.

Diesel injection shop I took my injectors to that was 100 miles from the ocean had no problems obtaining parts, didnít even want to know the engine it came from.
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Old 17-09-2019, 18:23   #7
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Re: Pre-combustion chambers

Quote:
Originally Posted by Jim Cate View Post
....
Good luck with the search... both of you! Digging through Wottie's shed ain't a trivial matter...

Jim
Well Jim's comment was spot-on; it did take some effort but finally located in a bag nicely labeled 2QM20 pre-com chamber!!!

Sadly for the OP, I'm sure it is the too big. Rough measurements are smaller OD - 24mm, larger OD - 34mm, total length (both parts) - 42mm.

My gut feeling is the 2QM15 pre-com might be the same as the YSE, YSB, YSM engines and if so, it could also be the same as the TS50 industrial engine. FWIW, I understand the pistons are the same for the YSE/YSB/YSM/TS50.

There are a squillion TS50 engines in SE Asia and aftermarket spares for them.

An example https://www.taiwantrade.com/product/...-1786947.html#
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Old 17-09-2019, 19:35   #8
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Re: Pre-combustion chambers

Thanks for all the responses and advice. I will replace the damaged chamber. I've attached a couple of shots of the head as taken off the block. Head looks fine so far. Bore and bearing journals really good. Both pistons had a bit of soot on them...not too much and both about the same.One piston had a cracked land but no scoring of bore.I ordered some new pistons/rings. These are same as TS 60 pump/ generator. Sourcing aftermarket chambers is a great idea. I've searched Alibaba and aliexpress but no luck with chambers for the TS engine. I'm sure they're out there somewhere. Cheers and thanks again.
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Old 17-09-2019, 20:35   #9
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Re: Pre-combustion chambers

A64pilot has a good point re trying injector shop too if you can't find pre-com on Aliexpress.
They are a good place for fuel pump diaphragms as well since the yanmar mafia wont sell you a diaphragm.They would rather sell you a lift pump for the princely sum of $360 here
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Old 17-09-2019, 20:48   #10
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Re: Pre-combustion chambers

I still think the TS50 pre-com will be the same as the TS60 - might be wrong though...
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Old 17-09-2019, 20:51   #11
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Re: Pre-combustion chambers

Forgot to add I'd be looking at the injectors as well with a hole like that in the pre-com.
Could have a nasty spray pattern
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Old 18-09-2019, 15:13   #12
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Re: Pre-combustion chambers

There is a possibility that the damage to the precom chamber was caused by a clumsy attempt to remove it somewhere back in its past. Are you also doing a valve grind?
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Old 19-09-2019, 17:33   #13
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Re: Pre-combustion chambers

Hello,
Found some aftermarket combustion chambers for $US 14 ex Singapore. Best price for same OEM part was $US179 ex Japan. The Yanmar mafia is indeed alive and well. I will remove valves and good chance they will get a lap as a minimum.
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Old 19-09-2019, 17:52   #14
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Re: Pre-combustion chambers

Excellent sleuthing! From 329usd to 179usd to 14usd!

What engine did the Singapore ones say suited?

Did they have aftermarket valves also?

Off topic but I note you have a 18' putt putt. Would you care to post some photos either here or by PM - I rebuilding an old 18 inshore day cray boat and need ideas...
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Old 19-09-2019, 18:23   #15
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Pre-combustion chambers

Quote:
Originally Posted by Compass790 View Post
Forgot to add I'd be looking at the injectors as well with a hole like that in the pre-com.
Could have a nasty spray pattern


I am pretty sure this was due to flame cutting, caused by a ďbadĒ injector.
Itís not uncommon, the Duramax truck engine didnít have pre combustion chambers, itís combustion chamber was in the piston like many Diesels, a bad injector would flame cut the piston on that motor.

Really really ought to pull your injectors and have them tested every now and again, maybe 500 hour interval? Fuel quality determines interval, so it will differ.

I am amazed the number of boaters that donít know injectors ought to be tested every now and again, and itís not just sailboat people either.
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