Disassembling a seized engine - stupid and boring questions ( pun intended )

Open for English requests from all countries!
Antworten
ItchyMike
Beiträge: 40
Registriert: Mi Nov 20, 2019 11:39 am

Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von ItchyMike »

Hi!

Me and my brother found a deal of a working NX250 in good condition being sold together with another half-complete NX250 with a seized engine for spares.

After having so much fun with my recently acquired NX250 ( thank you Michael for all the advice and help getting a nice rear shock and 17 rear wheel for my NX250! ), we decided that it would be a good idea to get another NX250 for him and I would get the half complete one for spares.

Today I reached the conclusion that it is finally time to put an end to the chaos that garage has become and decided to start taking the seized engine apart and put the spare parts away in boxes.

I must say that I am not a very technical person ( I can do basic maintenance like oil changes and some valve clearance jobs in pre-historic engines ), so there's a chance I may ask stupid questions ( at least I am sure there will be boring questions! ).

My questions:

- As I was taking the engine apart, I noticed this piece of metal missing in the engine case. Is this engine case scrap?
20210509_172259.jpg
- What is the tool that I need to take the clutch basket apart? I have never done it before.
20210509_172350.jpg
- The cylinder ( according to my mechanic ) has some wear and the rod is f*cked.

Having an engine for spares( it is a 249cc MD21 )... I was thinking...

Would it be possible to have the cylinder bored/coated/sleeved to 78x64.8?

Would I be able to find a matching piston?

Would I be able to find a god rod kit for this? Besides the cheap rods available in eBay, I could only find this: https://www.3pracing.com/en/samarin-spe ... -1990.html , but apparently noone ever tried it.

If I was getting into this, I would want something that could be used ( and I mean used, not used to be destroyed ).

Should I simply forget about a big bore project? :mrgreen:
Du hast keine ausreichende Berechtigung, um die Dateianhänge dieses Beitrags anzusehen.
Benutzeravatar
scrambler
Site Admin
Beiträge: 8200
Registriert: Fr Sep 14, 2012 8:50 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von scrambler »

ItchyMike hat geschrieben: So Mai 09, 2021 7:22 pm As I was taking the engine apart, I noticed this piece of metal missing in the engine case. Is this engine case scrap?
I think so. If you find the missing piece you might try to glue it into place – but even though there are very effective technical glues I would not have a good feeling about this.
ItchyMike hat geschrieben: So Mai 09, 2021 7:22 pm
What is the tool that I need to take the clutch basket apart? I have never done it before.
You need two – the holder and the socket nut https://www.ebay.de/itm/123650676025?ha ... Sw6CRcLeyW
ItchyMike hat geschrieben: So Mai 09, 2021 7:22 pmWould it be possible to have the cylinder bored/coated/sleeved to 78x64.8?
That seems too much, the sleeve is getting too thin. I guess 72-73mm would be the max - an engine specialist should know this.
ItchyMike hat geschrieben: So Mai 09, 2021 7:22 pm Would I be able to find a god rod kit for this? Besides the cheap rods available in eBay, I could only find this: https://www.3pracing.com/en/samarin-spe ... -1990.html , but apparently noone ever tried it.
Right, as far as I know nobody tried it. It might work – but then there is the problem to get the crankshaft apart without destroying is. A specialised workshop failed, which resulted in a bend crankshaft.

Lately complete Chinese crankshafts popped up https://de.aliexpress.com/item/10050020 ... web201603_
As usual with Chinese parts, its not given that they will fit or last.
ItchyMike hat geschrieben: So Mai 09, 2021 7:22 pmShould I simply forget about a big bore project? :mrgreen:
Depends on how much money you are willing to spend :)
sauve qui peut
ItchyMike
Beiträge: 40
Registriert: Mi Nov 20, 2019 11:39 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von ItchyMike »

Thanks for the feedback! :-)

The missing piece was teared into pieces in the bottom of the engine case, I don't feel comfortable with the thought of having a piece of metal glued inside an engine. :mrgreen:

I was having a look at this nice rebuild video ( that you probably know already ):

https://www.youtube.com/watch?v=F0QhpLJE1Hs

I missed the detail that they did not take the crankshaft apart ( after you mentioned it, I immediately thought that I had not noticed that ).

So, for this case, I would need ( at least ) an engine case, a crankshaft and a cylinder. I was not aware that there were aftermarket crankshafts available already, but I think I'll skip that as well. :mrgreen: But if someone tries it I certainly want to know.

If I am going to do a full rebuild that engine has to last at least another 30 years. :mrgreen: So genuine parts, or parts that have better specs than OEM and are tried and proven only.

Well, for know I am just going to finish disassembling the engine ( a nice didactic experience anyway ), and I'll keep an eye on any future developments regarding this engine's rebuilds.

Thanks again!
Benutzeravatar
scrambler
Site Admin
Beiträge: 8200
Registriert: Fr Sep 14, 2012 8:50 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von scrambler »

ItchyMike hat geschrieben: Mo Mai 10, 2021 2:52 pm I was having a look at this nice rebuild video ( that you probably know already ):
Yeah, nice video, but not suitable as a step by step manual. I have all the necessary pics to produce a how-to for disassembling the NX250 engine. But it doesn’t make much sense at the moment because pistons are sold out.
ItchyMike hat geschrieben: Mo Mai 10, 2021 2:52 pm If I am going to do a full rebuild that engine has to last at least another 30 years. :mrgreen: So genuine parts, or parts that have better specs than OEM and are tried and proven only.
Good idea, but not possible at the time being. While crankshafts are still available (expensive) the OEM pistons are sold out https://www.cmsnl.com/honda-nx250-domin ... Jodi6GxWcx Now having pistons reproduced in decent quality would not be rocket science but expensive. Some time ago I got an offer of 71mm oversize pistons for 270€ viewtopic.php?f=4&t=1095 but nobody was interested.

So at the moment you are far better off if you buy a second NX as a donor. In the future we have to figure out how to repair the original crankshaft, then we can have the pistons reproduced.
sauve qui peut
Zigomatix
Beiträge: 90
Registriert: Fr Jan 10, 2020 5:25 pm
Wohnort: France, Brittany

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von Zigomatix »

Hi, here is some guy selling his bike in parts, you may get the engine and some orther stuff ...
I already got the mufler, neiman and keys from him.

https://www.leboncoin.fr/equipement_mot ... 1481102916

good luck
Regards
Patrick
ItchyMike
Beiträge: 40
Registriert: Mi Nov 20, 2019 11:39 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von ItchyMike »

I am just assembling some information for curiosity and future consideration. :mrgreen:

I spoke with an UK company ( Langcourt ) that can repair/bore the cylinder and I was ( trying ) reading this topic:

viewtopic.php?f=4&t=161&start=10

If I understood correctly there's a possibility to fit other Honda piston in a bored cylinder?

scrambler, if you decide to revisit the custom made pistons subject let me know, I may be interested.

Thanks for the link, Zigomatix.
Benutzeravatar
scrambler
Site Admin
Beiträge: 8200
Registriert: Fr Sep 14, 2012 8:50 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von scrambler »

ItchyMike hat geschrieben: Di Mai 11, 2021 12:04 pm If I understood correctly there's a possibility to fit other Honda piston in a bored cylinder?

Must have overlooked that question :roll: . Yes, it looks like that a 71mm piston of the CBR900 Typ SC33 (1996-1999) https://www.ebay.de/itm/293544166134?ha ... ondition=4 may fit. Maybe with mods, an engine specialist should be able to figure that out. With 1mm more bore it would be perfect to repair worn out cylinders of the MD21 and it would be a boost for the 239cc MD25. And I was told that with 1mm more bore you could still use the original gaskets.

Bild
sauve qui peut
ItchyMike
Beiträge: 40
Registriert: Mi Nov 20, 2019 11:39 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von ItchyMike »

Cool, thanks for the info.

I must do some research on companies that repair Nikasil cylinders, I could then reuse the existing worn cylinder for this rebuild project.

As I mentioned, I know this one, but never dealt with them before:

http://www.langcourt.com

The question is if a repaired cylinder is as good ( or better ) as the original.
Benutzeravatar
scrambler
Site Admin
Beiträge: 8200
Registriert: Fr Sep 14, 2012 8:50 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von scrambler »

ItchyMike hat geschrieben: Di Mai 18, 2021 11:04 am The question is if a repaired cylinder is as good ( or better ) as the original.
If it’s properly done – why not. Newer two-stroke moto-cross engines often had nicasil cylinders and a lot of companies are offering boring and re-coating. Here for instance boring would be 60€ and recoating 260€ https://www.lanzaroad.eu/Zylinder-Reparatur_1
sauve qui peut
ItchyMike
Beiträge: 40
Registriert: Mi Nov 20, 2019 11:39 am

Re: Disassembling a seized engine - stupid and boring questions ( pun intended )

Beitrag von ItchyMike »

Will be a matter for research for sure. :mrgreen: btw, I sent you a PM a while ago.
Antworten