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Classic Bike Trackdays

SDR200 Head Gasket

 
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2TV owner



Joined: 22 Mar 2012
Posts: 145
Location: West Yorkshire

PostPosted: Wed Mar 23, 2016 10:07 pm    Post subject: SDR200 Head Gasket Reply with quote

I finally decided to look into why the sdr seemed to be using coolant. It looked highly likely that the head gasket had failed, so out came the motor one December Sunday and the head was removed on the bench. Not too obvoius from the picture but the gasket had failed at the back and was letting compression get into the cooling system and blowing the expansion bottle top off. Second oversize piston for the eagle eyed amongst you! this motor had been down before!

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2TV owner



Joined: 22 Mar 2012
Posts: 145
Location: West Yorkshire

PostPosted: Thu Mar 31, 2016 7:53 pm    Post subject: Reply with quote

So i decided to pull the engine apart as I didn't know it's history and being a mid eighties Japanese import it could need further attention. The bore looked fine with a nice clean cross hatch and very little if any glazing. The bike had always dropped a small amount of gearbox oil if left stood. Nothing to be concerned about but this was an ideal opportunity to resolve it once and for all.
As I lifted the barrel I quickly noticed that the piston had two inlet holes in it on the induction side. I knew as this engine has crank case induction it didn't need these holes. Furthermore there seemed to be quite a lot of carbon on the underside of the piston and on the little end. The piston was stamped 37F. A bit of research brought up that the piston came from a 1986 Yamaha DT200. Google images also revealed that the 37F motor had a carb mounted on the barrel and would therefore need the holes in the piston that I didn't.
I will add some more pictures to this thread shortly
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nikolas



Joined: 05 Apr 2016
Posts: 1

PostPosted: Fri Apr 08, 2016 1:53 pm    Post subject: Reply with quote

Hallo 2TV owner! Regarding your piston, it is indeed off a DT200 '84-'87. I still have one still working extremely well! As far as gearbox oil leak, check your gearchange lever shaft seal: it is a single-lip type (10-21-5mm) and it doesn't fit as snugly as it should in it's housing. Use a new one, grease the lip and shaft lightly and insert it in place using blue Hylomar or equivalent in it's circumference, paying attention not to put any of this stuff on working surface. I have found a (better) Honda double-lip seal (part number 91201-035-015). As you do not specify exact source of leak, all this is hypothetical, based on statistics...
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2TV owner



Joined: 22 Mar 2012
Posts: 145
Location: West Yorkshire

PostPosted: Wed Apr 13, 2016 8:03 pm    Post subject: Reply with quote



This is the piston as removed. Clearly not for a crank case inducted 2stroke motor.



Made in Japan, but not for an SDR200. I began to wonder why there seemed to be a lot of carbon on the underside of the piston and around the small end bearing and pin. I think this is because of the holes on the piston are letting some of the charge/gasses get back round the transfer ports and gumming up the underside of the piston.



Another view of the piston back in the barrel showing the ports being uncovered by the holes in the piston.



A shot of the cylinder head as removed



The motor was stripped fully, cases split, bearings removed and everything checked. All the gearbox parts were fine. I decided to replace the clutch plates on the rebuild along with all of the bearings and seals. I managed to get all of the bearings off/out apart from 2 in the left case. These did eventually come out but this was left to Shag at AJ's Vapour blasting who got them out when i took the cases over to him.
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James P



Joined: 31 Mar 2013
Posts: 121
Location: Sydney, Australia

PostPosted: Sat Apr 16, 2016 6:05 am    Post subject: Reply with quote

2TV owner wrote:
...I managed to get all of the bearings off/out apart from 2 in the left case.

Were they the needle rollers for the gearbox input shaft and the clutch lever shaft? I had some trouble with those ones - even after sitting in the oven at 150degC for half an hour, they still wouldn't budge.

I eventually discovered that they would come out fairly easily (without damage) using the correct size internal expanding bearing puller with slide hammer.

For the gearbox input shaft bearing, I set the bearing puller jaws just outboard of the roller casing (slightly into the well for the clutch lever shaft). For the clutch lever shaft bearing, I set the bearing puller jaws just inside the reinforced part of the roller casing, above the rollers. In each case, repeated gentle tapping with the slide hammer was enough to remove the bearings undamaged. I would not attempt this without heating the engine casing though.

Regards,
James
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2TV owner



Joined: 22 Mar 2012
Posts: 145
Location: West Yorkshire

PostPosted: Wed Apr 20, 2016 8:44 pm    Post subject: Reply with quote



After a bit of cleaning and polishing the power valve started to sparkle. A bit more work required.
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2TV owner



Joined: 22 Mar 2012
Posts: 145
Location: West Yorkshire

PostPosted: Wed Apr 20, 2016 8:46 pm    Post subject: Reply with quote



Right hand case split and de-bearinged, ready to go to be vapour blasted
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2TV owner



Joined: 22 Mar 2012
Posts: 145
Location: West Yorkshire

PostPosted: Wed Apr 20, 2016 8:47 pm    Post subject: Reply with quote



Cylinder head cleaned and faced up ready to be refitted, although when this picture was taken the rebuild was some time off!.
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