News:

The HOC Forum is here to provide information and assistance to all folk interested in keeping Hesketh V-Twins on the road.  You don't have to be a HOC Member to join, just register for an account and join in the conversation....

Main Menu

Valve Clearances

Started by Miti, December 14, 2013, 04:37:55 PM

Previous topic - Next topic

Miti

Whilst I've got most of the engine covers off my V1000, it seemed a good opportunity to check the valve clearances.  The V1000/Vampire Workshop Manual gives two different specifications:

Old (Factory) Specification:

Inlet:       0.10mm - 0.15mm (0.004" - 0.006")
Exhaust:  0.15mm - 0.20mm (0.006" - 0.008")

New (Modified Engines) Specification:

Inlet:       0.025mm - 0.050mm (0.001" - 0.002")
Exhaust:  0.025mm - 0.050mm (0.001" - 0.002")

I've heard much anecdotal information about the reasons for change and thought it might be interesting to list a few:

"The production engines were fitted with Hepolite pistons that were incorrectly marked so they were fitted in the engines back to front.  This presented the valve cutaways in the piston crowns to the wrong valves and necessitated an increased clearance to avoid valve clash."

"The cams were ground with lobe profiles that included 'quietening ramps' in the order of 0.004".  The factory valve clearances were so wide that these ramps were completely negated, resulting in horrendous 'top end rattle'"

"The wide valve clearances were used to reduce valve overlap and increase engine power.  The price paid for this was a very noisy engine"

"The V1000 engine is unusual in that the valve clearances actually increase as the engine warms up, so the only requirement for the cold clearance is that the valve actually close properly.  This can be tested by ensuring that the cam follower still rotates when the cam lobe is facing away from it.  A clearance of 0.001" to 0.002" is more than sufficient to permit this..."

I assembled a small selection of tools to carry out the task:


  • PIC: A Hesketh Valve Shim set: 18 sizes from 2.15mm to 3.00mm in 0.05mm increments
  • A valve grinding tool with rubber suction cup ends
  • A long/thin flat bladed screwdriver
  • A micrometer
  • A set of thickness or "feeler" gauges

First I measured (or attempted to measure) the valve clearances.

Front/Exhaust:  measured at 0.075mm and 0.090mm (both exceed the max limit on the new spec).

Front/Inlet:  Hmmm... The thinnest feeler gauge in any of my (many) mechanics sets is 0.05mm, so I could only meausure a tolerance at least as large as the largest permitted spec.  I couldn't get this gauge in between either inlet lobe/follower, so proving that the gap was <0.05mm.

However, the V1000 camshafts run on needle roller bearings, which afford a marvellously smooth rotation.  So smooth that any interference between cam lobe and follower may easily be felt... I could feel at least one of the inlet lobes touching its follower... So, I removed the inlet cam and removed one of the buckets/shims.  The cam now rotated without interference, so proving that the bucket/shim removed from the head was causing the interference (I did replace it and remove the other as a double check).  So, now I knew that I had inlet clearances of >0.05mm and >0.00mm.

PIC:  With the cams removed from the head, the cam followers or "buckets" can be clearly seen.  The V1000 runs a "shim under bucket" arrangement, so these must be removed to change the shims

PIC:  So, measurements taken, I now removed all four cam followers, using the valve griding tool.

PIC:  It works a treat - unlike trying to pull the awkward, oily buggers out with latex gloves on!! (That way madness, or at least blind rage, lies...)

PIC:  The shims tend to stick into the underside of the cam follower:

PIC:  But they're easily prized out with the long screwdriver.

PIC:  To work out the sizes of any new shims that may be required, it's important to know the sizes of the ones being removed.  This is most accurately done with a micrometer:

Then it's simple mathematics:

When the measured gap is too large; the calculation is "Measured gap minus required gap equals difference," then "old shim size plus difference equals new shim size".

For the largest exhaust clearance this would be:

0.09 - 0.05 = 0.04.  Then 2.35 + 0.04 = 2.39.  This isn't available, 2.40 being the nearest size available.

Note: Fitting a 2.40 shim will actually reduce the clearance to 0.04, which is still within the new spec...

When the measured gap is too small; the calculation is "Required gap minus Measured gap equals difference" then "old shim size minus difference equals new shim size".  For the smallest inlet clearance this would be:

0.050 - 0.00 = 0.05.  Then 2.25 - 0.05 = 2.20. 

In practice, the 2.20 shims in the kit were found to all measure slightly less than 2.20mm, so fitting any of them would make the clearance >0.05mm.  So, I took one of the 2.25mm shims originally fitted and ground it down to approx  2.23mm  This gave a calculated clearance of 0.02mm.

When reassembled, all four gaps were measured and found to be >0.050mm, the rotation of both cams was perfectly smooth, without interference and all four cam followers were free to move in the valve pockets...

So... Job Done..!! Time to move on to the rear head...

BTW:  When I take ownership of a new (to me) bike, I always check and record things like valve clearances during servcing.  This allows me to spot anything that's wearing out before problems are caused... For the valve clearances, I used a table to note down the results for future comparison.  The link is just a picture, but if you'd like a copy in MS Word, drop me a PM and I'll e-mail a copy to you.

Jeff
1974 Triumph T160 Trident (New Project)
1981 Yamaha XS1100 Sport (Trike Project)
1981 Yamaha XS1100 Sport (Red Sport)
1982 Hesketh V1000 (Production/Development Engine)

Hesketh Rider

Hi Jeff i have finally managed to get on to the forum hoping to open up some photos of the inside of one of these hesketh engines . your valve clearance post seemed as good as any , however when i click on pic it opens up something about sky holidays 2024 , internet carrier near me , and iphone holiday deals any idea whats going on or is it me
1x HESKETH V1000
1x DUCATI 900 SSD . 2x DUCATI 900 GTS
3x IRONHEAD HARLEY DAVIDSON .  1X HARLEY XLCR
1x ROVER V8 Street Fighter . 1x 1967 YAMAHA TD1C
1x BROUGH SUPERIOR PENDINE SAND RACER . 1x 1923 AJS LANDSPEED SPECIAL