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Still suffering from rotated photos...

Broke an intake valve spring pair on the way home from a trip yesterday, limped back on one cylinder.  Took it apart and no damage done other than the broken spring.  Cylinder and piston spotless.  I recovered an old spring set (inner and outer) from an old set of crusty Dnepr heads and have it running again.  But a bunch of questions arise....

The threads discuss weak Dnepr valve springs that suffer from overheating.  Fibre washers have been fitted by KMZ to insulate from the heat of the heads (my valve train has no such washers) and moreover this is the left head which is running considerably cooler than the right head.  This too is an anomaly as the threads pinpoint the left head as the hot runner.

The right head is running much hotter and the carb is barely toucheable.   I jacked the needles a notch to increase fuel cooing but no noticeable difference (Pekar K65T carbs).

I suspect I'm facing multiple issues - the Pekars are not responding well to adjustments although last year everything was running smoothly.   I'm also wondering from a reliability perspective if I should be changing out all valve springs so I don't get caught 500km from home...

I've reworked, refitted, repaired and adjusted the K65ts endlessly and wonder if there is a better option.

I also suspect these are two separate issues.  The heads I'm running now are poor quality,  slop in the guides, counterbores for mounting bolts way off center,  rocker arms misaligned with valve stems...  I might bite the bullet and have the original heads restored.

Any advice appreciated.

ND.

 

 

 

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I believe the problem with the springs is not the heat but the poor quality material of the springs. For example the Ural engines does not have this problem, also the boxer BMW aircooled engines which don't have an insulator shim under the valve springs.

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Thanks Luca.  I note Ural Zentrale sells upgraded valve springs for Dnepr 650 engines.   I suppose the question is if I upgrade the springs should I go the whole route and restore the original heads that do not have misaligned rockers, sloppy valve guides and bolt holes that are so off center that I had to machine special washers to get them to fit.  I'll have to think about this.

I suppose there are a lot of options for carbs but if anyone has a favorite alternative to K65T's that won't break the bank I'm all ears.

ND.

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Restore the original heads.  They are already removed from an engine and easy to access, and you've identified many issues with the heads presently on your bike.  You will thank yourself...

My son's '98 Ural had problems with crappy heads: poor running, inconsistent valve adjustments, excess heat and more.

He completely replaced them with new Ural head assemblies and his bike has run consistently with balanced increased power, valve adjustments holding for 10K+ kms, and now more than 102,000 kms on the dial.  Still running strong.

RussN

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