srx valves etc

[andy230]

Hello all,

I got the head off the racer last night.  In the frame, I may add- it was actually ok!

Anyway, I'm pleased beacuse-

the head looks ok
the piston looks good
the bent valve won't seat, pretty much confirming this as my problem.

So I plan to put it all back together, hopefully in time to get the last race of the season.

I have 4 stupid questions

1.  I'm skint!  Is it prudent only to replace the bent valve, reuse the (uprated) springs, collets, washers etc?  Or should I replace the small fiddly bits as a matter of course?

2.  Presumably I'll have to grind in the new valve.  Will this necessitate stripping the whole head??

2.  Should I get new bolts?  Its a hi comp 620 motor, the ones renowned for blowing gaskets...!

3.  Should I torque the head?  I've only ever done heads on Brit stuff, and these torque settings are always "as tight as you can get it" according to experts ie. Mick Hemmings.  I feel the Jap stuff is a bit more scientific, and should probably be torqued to a specific value.  Comments?

Thanks guys, any advice appreciated.  I'll get on to slipstream & see what they say as well.  Cheers for now

a

[Steve H]

1.  I'm skint!  Is it prudent only to replace the bent valve, reuse the (uprated) springs, collets, washers etc?  Or should I replace the small fiddly bits as a matter of course?

If it were me I would only replace the valve, the spring and collets should not have been damaged. However it would be good to know wheter it hit the piston due to float or incorrect valve timing. If the former then the springs might not be up to it and may need changing

2.  Presumably I'll have to grind in the new valve.  Will this necessitate stripping the whole head??

Would have thought so if your relatively clean with the paste

2.  Should I get new bolts?  Its a hi comp 620 motor, the ones renowned for blowing gaskets...!

Were they replaced last time ? If cheap I'd change them

3.  Should I torque the head?  I've only ever done heads on Brit stuff, and these torque settings are always "as tight as you can get it" according to experts ie. Mick Hemmings.  I feel the Jap stuff is a bit more scientific, and should probably be torqued to a specific value.  Comments?

Definately torque down evenly, Slipstream should be able to recommend values.
Also I'd

- Use a new genuine head gasket
- check the valve piston - clearance with some plasticine. The valve timing may be out. What cam is it and has the sprocket been slotted to accomodate the regrind ? (not always required)
- Check the valve guide to ensure not damaged/bruised
- Is it using the standard Yamaha rod or Carillo ?. Ive been told the Yamaha rods can stretch quite a bit if used above 8,0000 rpm. What revs were being used on the Dyno ?

Steve

[andy230]

Hi Steve,  Thanks for this

1. I'm skint! Is it prudent only to replace the bent valve, reuse the (uprated) springs, collets, washers etc? Or should I replace the small fiddly bits as a matter of course?

If it were me I would only replace the valve, the spring and collets should not have been damaged. However it would be good to know wheter it hit the piston due to float or incorrect valve timing. If the former then the springs might not be up to it and may need changing

Ok.  I'm pretty sure the contact occurred due to a faulty (sorry, disconnected and not secured!) decompressor.  The springs were new when I got the engine, about 2500 miles ago (some admittedly quite hard miles, especially recently!).  And they're uprated to compe with the lumpy cam.  Pretty sure they're ok...

2. Presumably I'll have to grind in the new valve. Will this necessitate stripping the whole head??

Would have thought so if your relatively clean with the paste

Steve, did you mean WOULDN'T rather than "WOULD have thought" ??  I'll be as clean as a lazy man can be to avoid stripping it!  New guide seal do you think?

2. Should I get new bolts? Its a hi comp 620 motor, the ones renowned for blowing gaskets...!

Were they replaced last time ? If cheap I'd change them

Yes they were changed last time, but may do again.  Will speak to Martin.  Cant be assed doing the job again for the price of 4 bolts...!

3. Should I torque the head? I've only ever done heads on Brit stuff, and these torque settings are always "as tight as you can get it" according to experts ie. Mick Hemmings. I feel the Jap stuff is a bit more scientific, and should probably be torqued to a specific value. Comments?

Definately torque down evenly, Slipstream should be able to recommend values.
Also I'd

- Use a new genuine head gasket
- check the valve piston - clearance with some plasticine. The valve timing may be out. What cam is it and has the sprocket been slotted to accomodate the regrind ? (not always required)
- Check the valve guide to ensure not damaged/bruised
- Is it using the standard Yamaha rod or Carillo ?. Ive been told the Yamaha rods can stretch quite a bit if used above 8,0000 rpm. What revs were being used on the Dyno ?

Steve

Gen head gasket- yep, won't risk rubbish necessitating a repeat job.
Valve timing- its a Kent stage 2 grind on the cam.  The cam was dialled after the last build, I believe using a slotted sprocket.  I marked it on disassembly but slots weren't obvious...  Will look again tonight.  Won't check with plasticine- it was good before.  As I say, I am certain it was the decompressor turning thru 180 degrees.  There are marks on the exterior of the top fin where the piston has hammered the wee lever into the fin (via my now bent valve!)
Will examine the guide on disassembly
Standard Yam rod, thus standard red line.  Can't afford Carillo Ti rod unfortunately!!

One more question:  How do I plug the hole left by my soon to be removed decompressor mechanism??  Might have to gt on to Martin sweet re this one.

Cheers for the advice!

a

[Steve H]

Some cams dont need the sprocket to be slotted, the German cam I was using was a good example (but me being me I checked it anyway).
As for the decompressor, wouldnt it be easier just to fit a cable, or has the kickstart mechainism been removed as well ? Another option is to cut the offending cam off of the decompressor lever so there is no possiblity of it doing the dirty again.

[themoudie]

Aye Andy,

Pleased to see strip was trouble free. Concour with SteveH comments and your responses.

As for skint racer bunging up a hole!

I assume this is permanent racer, so always bump or roller start. Kick start and decompressor just superfluous excess baggage! ;-)

I've just been out to check and a 1p peice of the Realm's coinage fits nicely. Remove the offending mechanism and oil seal. Clean the hole and coin with brake cleaner. Then 'monkey metal' or Araldite the coin in place, your last penny put to good use.

If the penny gets shot out you know that either your valves or the guides are knackered!!

Regards, Bill

[andy230]

Cheers Bill

Actuially, I'd always want the option of converting back to road use, but I suppose the seal could be replaced, and the araldite removed...

Cheers for the tip!

a