2008 Rev 3 270 Motor Rebuild

[Stakes]

Hi there,

Just torn my REV 3 270 motor down for new bearings and seals and am going through other items whilst I wait for parts. I've never used the bike as it had a few issues when I bought it. I have a few questions please - some may be dumb but its been 10 yrs since I had a 2 stroke apart and a few brain cells have said rendex vous, if anyone can help:

1) Rings - My bike has a Vertex piston (I'm not sure whether this is the original make of piston) looks in good condition. When I push the rings into the barrel the 2 ring gaps measure up at 0.5 and 0.7. I've read in the evo manual that the gaps limit is 0.6mm. Do I leave or replace? And if I use as is should I put the smaller clearance at the top.

2) Does anyone know the dims to measure a 270 piston and also the 270 cylinder bore as the evo workshop manual only states 250 and 290 specs but am I right in thinking most of the 2008 motor is the same?

3) The stator backplate is slotted. How do I know the correct position?

4) When setting the squish with some soft solder to choose the base gasket (mine had 0.5mm) can I reuse the head gasket or is it once use only?

5) I've just fitted all new bearings in the cases and the manual says to heat the mains before fitting the crank. I'm worried that I will damage these expensive new crank seals. I can turn up a protective plug to drop in whilst heating but is heating necessary. I cant remember doing this on my old Honda RS race bikes years back?

6) The UK 270 has an extra flywheel weight. Should I refit this?

Matt

 

[mcman56]

I have a few responses.

 

1 - Probably not essential but desirable.

2 - The evo and rev motors are almost exactly the same so the manual is good.

3 - Generally set in the middle.  Full advance can sharpen the response a little.  Full retard can dull the response.

4 - 0.5 mm is on the tight side.  1.0 is the usual recommendation.  It is best to replace the head gasket but I have reused them with some copper spray-on head gasket sealant.

5 - You can use a round piece of aluminium a little smaller than the outside diameter of the inner race of the bearing.  Sit this on the inner race, heat the aluminium and let it transfer heat to the inner race.  I used a black anodized piece of aluminium and it was heated enough that it turned kind of a gold color. 

6 - It depends on the type of response you want.

[Stakes]

21 hours ago, mcman56 said:

I have a few responses.

 

1 - Probably not essential but desirable.

2 - The evo and rev motors are almost exactly the same so the manual is good.

3 - Generally set in the middle.  Full advance can sharpen the response a little.  Full retard can dull the response.

4 - 0.5 mm is on the tight side.  1.0 is the usual recommendation.  It is best to replace the head gasket but I have reused them with some copper spray-on head gasket sealant.

5 - You can use a round piece of aluminium a little smaller than the outside diameter of the inner race of the bearing.  Sit this on the inner race, heat the aluminium and let it transfer heat to the inner race.  I used a black anodized piece of aluminium and it was heated enough that it turned kind of a gold color. 

6 - It depends on the type of response you want.

Thanks for the fast reply.

I'm pretty sure the crank seals were shot when I bought this bike as it would start, rev its tits off then cut out. The barrel looks good but the head has a lot of detonation marks. Maybe this was down to the crank seal or the squish was too tight. I'll try a 1.0mm base gasket and measure. I've read elsewhere that 1.0-1.5mm is correct. Which would you choose. I'm a 49yr young novice rider at trials and come from enduro and road racing.

Great tip on the bearing slug. I'll turn a top hat bush hat sits inside a little.

On the timing I read that the gap should be 7.0mm from the right side of the bolt / screw to the left side of the slot. Is that applicable to the 2008 270 - it would leave it pretty much near the middle? Would advancing be increasing the slot gap on the right (ie. turning the backplate anti-clockwise)?

[mcman56]

1.0 is probably more standard. 1.5 would drop compression a little.. maybe making it easier to kick, more detonation resistant and possibly a little softer in power.  People add extra base gaskets exactly for those reasons but I have never done it so don't know how much of a difference it makes.  I have a friend that recently went from a standard compression head on a 250 evo to a lower compression head and can not tell a difference so maybe you have to be sensitive to small changes to tell.

Rotating counter clockwise should make it trigger earlier and advance the timing.  I don't have a spec for a 2008 270 but most everything I see shows it about in the middle so it would be the safe place to set it.  Certainly not the same bike but I recently had a 2008 200 and changed from mid position to full advance.  Pick up off of idle was slightly quicker but barely noticeable.  It did not detonate but another bike might.  

 

[Stakes]

With lifting the cylinder up you are also lifting all the ports and lifting the exhaust is counter productive to what you are trying to achieve so I guess thats why he went with the low compression head I guess.

Also I sourced some bearings from my local bearing supplier for the bottom end. They are all the same as I removed, SKF Explorers and C3 where necessary. The mains are open with neither steel or plastic shields. The bearings I removed did have metal shields. Are these open bearings going to be ok or should I get metal shielded? The ones I have bought are 6206/C3 SKF.

[mcman56]

If you want to soften off idle power, wouldn't lifting the cylinder be a good thing.  I think that is where most people struggle with trials bike power hence the use of flywheel weights.  I once heard a vintage trial rider describe modern bikes as abrupt.

My 2008 had open bearings with no seals.  At some point, Beta went to sealed bearings that look just like wheel bearings.  I recently rebuilt an evo and it had sealed beings and that is what I put back in.  Splat shop sells them.  I have never seen main bearings with metal seals but have not had that many bikes apart so am no expert.  However, i would think you want them open to get lubed by premix or well sealed with a lifetime worth of lubricant.

https://www.splatshop.co.uk/sherco-crankshaft-bearings.html

 

[pindie]

Just done my 2012 Evo mains. The old were metal sealed. New ones in Beta packets from a dealer have rubber seals. The case seals were also full rubber. Working fine at the moment now back together. Sounds very smooth. I removed the flywheel weight as it caused the bike to run on too much for my liking. I had to change gearing and throttle also to a slow one. 
 

I heated the bearings to fit back to the crank with a hot air gun with it angled not directly into the seal. Lots of little rests and misting the seal with iced water spray seemed to work- I love the top hat idea though. Once hot, drop case on before heat drops, bolts in and tighten evenly and quickly. Seemed easy enough. Worst bit was getting the shift drum and selector wheel all in place nicely.  
 

My 300 was nasty Before. Didn’t enjoy it before. It had a 0.5 base gasket. I replaced it with a 1mm gasket. Much smoother power now and more enjoyable. I’m also an older rider, mainly enduro. Trials just helps development/maintainability of skills. Probably.