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Author Topic: valve clearance question  (Read 42714 times)


  • Learner rider
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Re: valve clearance question
« Reply #50 on: August 26, 2012, 01:55:20 PM »

110,000km and still going strong - although i think it may be about time to at least CHECK the clearances... hmm probably should do cam chains while i'm at it!

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Re: valve clearance question
« Reply #51 on: November 02, 2015, 01:36:42 AM »

....Are there any special tools for this check and adjustment...

Valve clearance checking is really only a quality control item following manufacture of your engine. With reasonable metallurgy used over the last 25 years, after the 1500km check it should never need checking again, until you need to break apart an engine (remove the heads) due to high kilometres/miles to replace pistons/rings.

During assembly, most manufacturers will have up to 20 different stem length valves to choose from (easier than shims), and based on pre-assembly measurements of the heads the appropriate valve length is chosen for each valve.
Unfortunately, the annealing (metal hardening by heating and cooling repeatedly) process takes place when you use the engine and not everyone observes the correct break-in procedures.
Because of this, the valve clearances can alter during the run-in period due to valve seat regression (the soft metal of the head where the valve seats on can be abraded or hammered away).

Valve clearance checking is quite simple but time consuming. In addition to the normal range of tools, you will require a quality set of "Feeler Gauges" to do the check. It is all in the service manual.

In short, remove tank, camshaft covers, manual rotation cover and timing mark plug.
Rotate engine to get front cylinder at correct camshaft sprocket marks.
Insert various thickness feeler gauges to measure the cap/cup/tappet to camshaft clearances.
(see parts manual figure 8 items 8, 9, 13 & 14) http://www.hyosung.hu/download/pdf/data/alkatresz-katalogusok/GT650%20PART%20CATALOGUE.pdf
Clearances may decrease over the run-in time if the valve seat on the head (in the combustion chamber) regresses.
You must write down the "exact accurate measurements" for each valve.
If excessively out of spec then remove the cam shaft.
Next using a magnet you lift out the valve cap/cup/tappet and inspect the size of the shim that is underneath (may or may not have any).
Write this down next to each measurement made earlier.
Now do the maths to recalculate what sized shim is needed to replace the existing shim (if fitted) to make the required valve clearance fall within the OEM spec.
Write this down next to each measurement made earlier.
Now you do all the other valve caps/cups/tappets that were out of spec.
Now you order the required thickness shims and wait for delivery and then replace the out of spec shims and re-assemble everything.

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