seizure disaster. should have known better

A place for LC enthusiasts to hang out!

Moderators: rztom, 2smoke

Message
Author
graham heise
Posts: 291
Joined: Sun Sep 16, 2012 7:10 am
Location: gold coast Australia

seizure disaster. should have known better

#1 Post by graham heise » Tue May 22, 2018 7:17 am

I have been running in the lc i recently bought. On the the 5th ride i rode up a steep twistie road, mainly 1st and second gear, rolling throught the 3-6g rev range. The bike was running really well.
It started easy, pulled well and sounded healthy. At the top of the hill i was in the middle of a u turn to go back down and the engine stopped. I thought maybe i had brushed the kill switch or the electrics cut out. I checked over the bikes electrics then kicked it. started no problem and back down the hill i went.
Since then i have riden another sedate 200k's and then started to ride the bike in the band. With the bike warmed up it went for wof third gear. it didn't seem to pull up top (7-9), felt lean.
Yesterday i decided to pull the carbs to up the stock mains to 240's for the chambers. Once i had the carbs of decided to pull a reed block of to inspect the cylinder and piston. first thing i noticed was the bolts for the reed blocks were loose, 2nd thing no gasket bettween block.
Once out my wors't fears. seizure marks on the bottom inlet skirt. today i pulled the barrell. farrk. piston has a 4 corner seizure marks. minimal on exhaust side, mostly inlet bottom.
Before i bought this bike i spent hours on this and other lc forums. i had read on this forum about inlet skirts (removing middle tang) I asked the prior owner if he was aware of this mod and had he removed the middle tang. he said he had. Well that tang is here and now i feel cheated and deflated.
Kicking myself that i didn't spray starter fluid around carb joint to check for leeks. there had also been a little bit of oil around outside of reed block that i haden't noticed. i went over this bike for hours before running it up the road.
Note to self. any other 2 stroke that i buy pull the motor down to inspect, measure, and change all seals and gaskets to genuine.
Cause of this problem was no gasket between reed cage and cylinder. $4 part. sealant even cheaper.
The cylinder is in reasonable condition, hopefully a light hone. At minimum it will need a new piston, and a hone. I'll seperate the cases to inspect the crank. At least i can confirm it's a new hot rods crank, i hope it doesn't need a rebuild. Thing is i didn't at the time recognise the bike had seized at the top of that hill. It's since travelled another 200k's and i thought it was running great.
I have looked through the reciepts that came with the bike. 01/03/2012 yambits reciept. 2 ptk027 rdlc350 piston kit+2.00mm 98.91 usd. If you look at yambits with same part number it lists for rd400.
Now do i order the same piston to match the one in the other bore that looks great and do the skirt mod or do i buy a pair of now available small window flat skirt lc matika's. one thing that i had reservations about buying this bike was the 2mm overbore. doesn't leave many rebuilds. fingers crossed it hones up.
yamaha fanatic.

User avatar
JonW
Posts: 10599
Joined: Sat Oct 10, 2009 4:33 am
Location: Sydney
Contact:

Re: seizure disaster. should have known better

#2 Post by JonW » Tue May 22, 2018 9:46 am

Bugger, sorry to hear that Graham.

Hmm, I would always recommend a leak down test with any bike thats just been built or bought, that should have found this leak. But I think you might get away with this:

- The small tang isnt really about seizures its about it catching on the cases, and it seems thats not your issue which is running too lean cos of the air leak.

- The part number is often shared if the part works for more than one bike on the yambits site, see the list below when you search on that part number:
https://yambits.co.uk/advanced_search_r ... g1&x=0&y=0" onclick="window.open(this.href);return false;

- What I would say is that I have had a set of what Yambits now supply on this part number, ie Taiwanese Mitaka pistons, in my hands of this exact size and if thats what you have in there then they are truly nasty and I would be wary of them. Sand cast and badly done with nicks and poor attention to detail, ie flashing still present on piston windows etc. This would be a good opportunity to swap them for something nicer. TKRJ or Japanese Mitaka are a world apart from the Taiwanese ones IME. Of course 6 years ago that part number might have netted you a better class of piston... lets hope so.

- You may well be able to wash the alloy off the bore with some acid. Lets hope you dont need to rebore.

HTH
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

graham heise
Posts: 291
Joined: Sun Sep 16, 2012 7:10 am
Location: gold coast Australia

Re: seizure disaster. should have known better

#3 Post by graham heise » Tue May 22, 2018 4:25 pm

Thanks for your thoughts jon w. The inside of the piston reads prox made in japan. Maybe i can buy another?? What is right part number?? I have wossners in my rz and they have copped a floggin and still look great. . They need a larger piston to bore clearance then cast pistons. .06mm so depending on the hone and measurment of the cylinder that could be a possible route. The next time it needs a rebuild i may have to consider nikasil plating to continue to use the cylinders.

Sent from my SM-A520F using Tapatalk
yamaha fanatic.

Headcoats
Posts: 848
Joined: Sun Apr 04, 2010 6:13 am
Location: Pig On The wall Country

Re: seizure disaster. should have known better

#4 Post by Headcoats » Tue May 22, 2018 5:35 pm

Lucky escape I would say and you found the fault before a major disaster
Cryin' In The Beer Of A Drunk Man

User avatar
JonW
Posts: 10599
Joined: Sat Oct 10, 2009 4:33 am
Location: Sydney
Contact:

Re: seizure disaster. should have known better

#5 Post by JonW » Tue May 22, 2018 7:29 pm

Yes looks like the part number used to be for ProX and is now Mitaka. Just search for Banshee ProX pistons in 66.00, thats what youve got now, if youre wary buy two.

You can go to Wossners, but bare in mind that the bore will probably not need to be made bigger to fit them, the chances are the pistons are slimmer to get the clearance instead. Anyway worth a measure of your parts of course.

I bet plating the cyls costs more than a set of lower bore cylinders.... maybe its time for a big bore! :)
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

graham heise
Posts: 291
Joined: Sun Sep 16, 2012 7:10 am
Location: gold coast Australia

Re: seizure disaster. should have known better

#6 Post by graham heise » Tue May 22, 2018 9:13 pm

Hope i have avoided disaster headcoat. Your right again jon w. Wossners are undersized to allow for clearance. I'm taking the cylinder to engine shop this afternoon for measure and opinion on honing. Once i see how that goes i'll get piston or pistons. I have ordered new genuine yamaha seals and gaskets. Thanks for the advice fella's. Who sell's a good leak down test unit? Was tbinking i'd make one but i'd be happy to pay for a good one.

Sent from my SM-A520F using Tapatalk
yamaha fanatic.

tacky1
Posts: 950
Joined: Wed May 13, 2015 1:11 am
Location: Pacifica,,

Re: seizure disaster. should have known better

#7 Post by tacky1 » Tue May 22, 2018 9:21 pm

I use this kit on any engines I have built, Works great and Ive yet to have any probs with it..

https://www.ebay.com/itm/Yamaha-Tzr250- ... SwuhhXVuX0" onclick="window.open(this.href);return false;
1985 RZv500
1984 RZ500 Hybrid
1986 RG500 Walter Wolf
1986 RG500 Skoal Bandit
1984 RZ350
1984 RZ350 Hybrid
1981 RD350LC
1981 RD350LC Hybrid
2009 CR500AF Supermoto 250X
2007 CR500AF 250X
1988 YSR50 (2)
1984 GPZ750 Turbo
1989 VFR750R RC30

User avatar
JonW
Posts: 10599
Joined: Sat Oct 10, 2009 4:33 am
Location: Sydney
Contact:

Re: seizure disaster. should have known better

#8 Post by JonW » Tue May 22, 2018 9:40 pm

That kit looks quite nice actually. Tho if youve a big leak you wont find it with that small pump, fine for a very sealed engine tho.

Dan on Norbos forum also sells one, but you could quite easily make your own of course. I have Dan's kit and Ive made some of my own parts to replace his 3D printer parts that couldnt take the Aussie garage temps and delaminated or became brittle and broke. For my 421 I used some plumbing pipe caps and some pool bungs... it takes all sorts and a bit o lateral thinking but you can easily do it G.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

graham heise
Posts: 291
Joined: Sun Sep 16, 2012 7:10 am
Location: gold coast Australia

Re: seizure disaster. should have known better

#9 Post by graham heise » Wed May 23, 2018 4:13 am

Had a quick chat with Macca the resident bike engine builder and machinist from the gold coast, he didn't like the look of the bottom of the cylinder lining below the inlet . some scrape marks there. . He was busy building a crank but said without a new piston i can't tell till i mic it all up. His thoughts were to bore saying there is still enough liner it's only .25mm each side to go another .5 over.
The current bore has only travelled 3 hundred k's since it was bored so piston to bore clearance should be in spec everywhere else. If it has to go another .5 then so be it but i'll be keeping an eye out for the impossible, a set cylinders if they ever come up. i do have ypvs engine rebuilt sitting on the bench but i want to go with original. i'll be disassebling the rest of the motor and will take the other piston for referance.
yamaha fanatic.

graham heise
Posts: 291
Joined: Sun Sep 16, 2012 7:10 am
Location: gold coast Australia

Re: seizure disaster. should have known better

#10 Post by graham heise » Wed May 23, 2018 4:14 am

Cylinder.Image

Sent from my SM-A520F using Tapatalk
yamaha fanatic.

User avatar
JonW
Posts: 10599
Joined: Sat Oct 10, 2009 4:33 am
Location: Sydney
Contact:

Re: seizure disaster. should have known better

#11 Post by JonW » Wed May 23, 2018 4:23 am

It doesnt look great, but give it a hone and see what it comes out like, sometimes it will still be in spec.

You can find cyls easier in UK, Canada etc. Here its not easy but Ive contacted a mate who might have a set, no promises tho.
Last edited by JonW on Wed May 23, 2018 4:43 am, edited 1 time in total.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

graham heise
Posts: 291
Joined: Sun Sep 16, 2012 7:10 am
Location: gold coast Australia

Re: seizure disaster. should have known better

#12 Post by graham heise » Wed May 23, 2018 4:43 am

thanks again jon w. i'll get it honed and see where it's at. hopefully it can be salvaged. i feel really dissapionted in myself for not picking up this air leak before it happened. Although the bike idled well at 1200rpm and normally with any air leak the rev's will rise at idle and the temp gauge will climb when riding. I suspect the reed block bolts came loose whilst riding. Years ago my rz started to rev higher when at idle and that was traced to an air leak at the reed block. i should have known better. i'll be using loc tight and race wire from now on.
yamaha fanatic.

User avatar
two-stroke-brit
-----
-----
Posts: 1701
Joined: Fri Nov 22, 2013 10:49 pm
Location: Houston texas

Re: seizure disaster. should have known better

#13 Post by two-stroke-brit » Wed May 23, 2018 1:58 pm

graham heise wrote: i'll be using loc tight and race wire from now on.
thats a good idea on those bolts around the inlets .

i had a plug come loose and eat my motor (happens quickly)
350LC,Athena 392 big bore,stock porting,swiss cheese air box,stock reeds,spec11 pipes.(now TSA big bore pipes)
She might not be pretty but she will always be a fun ride


1982 YAMA RD350LC
98KDX 220R
1967 TRIUMPH TIGER
2001 TRIUMPH TT600

User avatar
2smoke
Moderator
Posts: 1005
Joined: Fri Dec 11, 2009 9:56 pm
Location: Niagara Ontario Canada

Re: seizure disaster. should have known better

#14 Post by 2smoke » Wed May 23, 2018 10:13 pm

That really sucks. Especially with a new bike.
Mine ate a piston last summer on a very busy highway in the passing lane doing around 130 kms/hr.
I pulled the clutch lever in quickly so the rear wheel didn't lock up. Still a pucker moment.
Cleaned the aluminum off the bore with toilet bowl cleaner. Less than a week later back on the road.
Colin
79 RD400F Daytona Special
81 RD350LC
89 TDR250
75 Kawasaki H1 500
77 Can-am Tnt250

hondaror
Posts: 2828
Joined: Mon Mar 03, 2014 8:44 pm
Location: Alberta, Canada

Re: seizure disaster. should have known better

#15 Post by hondaror » Thu May 24, 2018 2:31 am

That wear is excessive piston to bore clearance. The piston was rocking front to back.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

Post Reply