SV1000 Portal - View Single Post - Setting cam lobe centers without adjustable gear sets
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post #12 of (permalink) Old 18th December 2014, 05:06 PM Thread Starter
schmidt314
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Join Date: Nov 2005
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Quote:
Originally Posted by yamman37 View Post
An excellent write up. Mr Schmidt you are indeed a top man! I am considering this mod and would welcome your thoughts on the following:

1) Effectively the retiming involves a 26.226 crank degree advance of the idler pulley (one tooth on camchain side) compensated for by a 17.561 retard of the installed cams. The result being a 5.665 crank degree advance for both inlet and exhaust cams producing timing figs. of approx (+or- 1 degree) IN opens 13 deg BTDC, IN closes 45 deg ABDC, EX opens 47 deg BBDC, EX closes 9 deg ATDC. I calculated LC's of 106 inlet and 109 exhaust from this. Not identical to you but certainly in the ball park. My first question is have I got this right?

2) Would you recommend measuring std timing before beginning and then do the calculations, etc or is it safe to assume that differing tolerances will not be so great as to have to worry and just go for it? My greatest fear would obviously be Inlet valve/piston contact. But then you say it works with added compression so maybe it would be nicely safe with my standard K4 crowns. Unless of course you're talking HC pistons with deeper cut outs. Hmmm.

3) If the heads have got to come off to measure piston/valve clearance would you recommend a mild skim to raise compression? Or the barrels? It's very much a road bike so I'd be looking for 12:1 max.

4) If you see my first post (this is 3 of 3) you'll see my bike came without much of a top end at all. Both owners had literally kept it wrapped in blankets in dry sheds and cosmetically it is excellent but I think most of the maintenance stopped when it was out of warranty (@13k, now 26k). The chain alone made me cry and as for the airfilter..talk of a minger! Hopefully a K and N, removal of STV butterflies, desnorkelling and a throttle valve balance will restore at least some top end. Can you reassure me that the cam advance won't take some of it away? Oh and finally (topic drift I know) I'll test compression, but do you have to remove cams, remove decompressors, refit cams, test, remove cams, etc, etc, what a pain. The manual says not but one of your posts indicates you need to. Confused.

Cheers
Mick

Ps. For sake of amusement I should tell you that as a kid I thought the best way to set valve clearances was 1 thou IN, 2 thou EX, set at finger burning red hot. Not quite as daft now!
1. You do have it right. There are 31 gear teeth on the chain side and 41 on the cam gear side. This creates 31 possible possible positions so there are lots of possibilities to choose from.

2. I would measure you exact machine. This would assure you you know what you have and what you are getting. I only see about 2 degrees variation between the motors I work on when they are all stone stock. Cam chain stretch, cylinder height, cam gear installation, and head thickness can all be factors. In general with a stock engine you won't be even close to worrying about piston to valve interference. These motor are very spacious and forgiving when stock. You can mill heads and cylinders to increase compression a fair bit and still have plenty of room before smashing bits into each other. It is always best to measure though. You can also measure piston to valve clearances by stacking adjustment shims. For example if you currently have a 3.00 shim installed and you are wanting a minimum of 1.0mm piston to valve clearance. Place a really thin shim on the valve like a 1.20mm, then put a 2.80 on top of it. The 1.20mm shim is thin enough that the second shim will still be captured and held in place by the recess in the valve spring retainer. Now the valve is at 1mm more lift for the whole cycle and the engine can be turned over slowly and checked for interference. Note that this can be used for a stock bike because the springs will not coil bind, but just mindful of this and also that if you are really close to hitting stuff, please take valve clearance into account.

3. Added compression is a really good thing for these motors. With added compression from milling the deck height down, milling the head down makes really nice mid range. I would recommend this to anybody. Setting the squish values down to 1mm or a bit less, and then milling the heads to set final compression ratio is a great way to go. With stock cams, and running pump gas you can still go more than 12:1, but that number will work fine.

4. With added compression and cam timing there is no doubt you will should see better power from idle to redline. With just the cams, you should also get a little more punch through the midrange w/o sacrificing power else where. If you thin you feel a drop off, it is an easy thing to set the engine back to stock timing and go from there. The decompressors can be disabled easily with cams in the bike. I ususally cut the very end tip off a zip tie and wedge it into the weight so that it is stuck in the out position to disable the decompressor pin from contacting the bucket. You can test the compression as per service manual, but that does not give a full reading. I like to know what the real number is in many cases. I like doing leak down test personally, but a simple compression test does tell you whole bunch about engine health.

-MS


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