Cam timing.

I’ve purchased some steel helical gear wheels from Gutsibits earlier this year for the cam timing, and not being confident that the markings were correct as they were probably from an earlier model/different cam, I have decided to check the cam timing myself. IIRC from my workshop manual for the V7, 750S & 850T, basically you put the engine (on one cyl) to TDC, then set the valve clearance on that side to 0.5mm, zero in your timing degree wheel to TDC, and turn the engine until the tappet clearance has gone on the exhaust valve and that point should be 52* BBDC on the LM 1. All well and good. I have achieved this. What’s slightly concerning me is that when I have checked the cam wheels using the markings that were already marked on, using the above method and then the standard chain and chainwheels, I got exhaust valve clearance gone/ valve starting to open at 85 * BBDC and 80* BBDC respectively. I am confident in my readings, but does a chain really run 30* advanced? Or does this strongly suggest that I’m not as clever as I think I am? Have any of you done this yourselves, and what readings did you get?

ReggieV2012-10-10 16:41:38

Which model is it exactly? The 750’s are different.

850T, 850T3, 850 Cali V1000 etc.
inlet opens 20° BTDC
inlet closes 52° ABDC
exhaust opens 52° BBDC
exhaust closes 20° ATDC

750S, 750S3

inlet opens 40° BTDC
inlet closes 70° ABDC
exhaust opens 63° BBDC
exhaust closes 29° ATDC

If I remember rightly the camshaft drive pin is around the 9 O’clock position @ TDC on compression stroke, RH side


Appendix ~ MG workshop manual says rocker clearance is set to 1.5mm when doing this with a timing disc. (?)

Mike H wrote; Haynes:850T, 850T3, 850 Cali V1000 etc.inlet opens 20° BTDCinlet closes 52° ABDCexhaust opens 52° BBDCexhaust closes 20° ATDC It’s the LM MK1, so the same as the above. I’ve just read Guzziology on this subject (never thought to earlier) and “This old tractor” on line. It seems that there are discrepancies and contradictions in Motos own info etc and that it is easy to come up with incorrect figures. Apparently it’s a case of getting the opening and closing points of the cam done by oneself and then comparing them with the spec (as above) and “centralising” them as if you were using a piston stop on a piston to work out TDC on a timing disc (if that makes sense?) Looks like I need to go back in the garage.
ReggieV2012-10-10 19:08:33

As Mike says you need to increase the tappet clearance to clear the ramps on the camshaft while checking the timing.
Brian UK2012-10-11 09:12:56

Brian UK wrote; As Mike says you need to increase the tappet clearance to clear the ramps on the camshaft.Brian I’ll try this, but will also do as I said above at the same time. The manual that I have referring to the V7, 750S and 850T does say 05mm, but I have read that different tappet settings were introduced. Thanks.

If they are of Guzzi manufacture which model are the helical gear set from? IIRC Guzziology states that it might not be just a straight swap for gearsets from early bikes in the big twins series.

guzzijack wrote; which model are the helical gear set from? I don’t know. I bought them from Gutsibits earlier this year. I’ll have a read up on this just to make sure I’m not missing anything, but they were fitting OK yesterday, so I think they should be OK. Thanks for the prompt though.
ReggieV2012-10-11 21:02:47

Not wishing to throw flies into the ointment but there’s a possible problem with helical timing gears, in terms of the longitudinal end thrust on the camshaft, either pulling or pushing, not sure which way it goes, I was told a story about this a few years ago but can’t remember the details. It was making horrible noises anyway but can’t remember what he did about it.

helicals screw the camshaft into the little thrust on the camshaft. I fitted some on the spada and they were removed within 1000 miles the noise was horendous especially on the over-run I went back to chain and sprockets

there was some metal ones cut with straight teeth

Ex smokingbiker wrote; the noise was horendous especially on the over-run I went back to chain and sprockets Thanks for cheering me up Mike H and Brian uk, I have re-timed the cam using 1.5mm clearance on the tappets as you informed me to,using the markings that were already on the sprockets when they came into my possessio, andn both the opening and closing of inlet and exhaust is spot on, so thanks for the spot on info
ReggieV2012-10-13 18:01:06

There ya go, super