Soooo i took the missus car out thursday morning and came home on one of these. Problem being a snapped cambelt.(New belt and tensioners replaced in september btw) Anyway heres the outcome of that! Anyway i decided rather than get a used head(350) i would rebuild this one so i bought new valves,top end gasket kit,stretch bolts etc. The guides are all fine so thats all good. Its a long time since i lapped new valves in (last car was a 350 small block chevy) now i tend to use a drill attachment with a rubber hose on the stem end and ive so far done 2 exhaust and 2 inlet. Im just wondering if the new valves are stupidly hardened?As ive read plently of conflicting advice on the tinterweb about how long to grind them in on vw's? I know the principal behind it and ive got a decent 1mm grey line on all 4 valves by lapping them 10 mins with course and 15 mins with fine but just wondered if anyone had any experience lapping in NEW vw valves? Car is a 1.6 16v AZD lump. ....and no she wont let me put a 1.8t in it :drool:
If its anything to go by the bores are perfect and ive filled them up with petrol to check for leakage and there is none.
Ah ok i see.But surely if the bore isnt marked in anyway this would indicate they are ok?As a pinched ring would expand a little causing a score/scratch on the cylinder bore wall? I dont really want to pull the pistons out as i hate taking the sump off this thing,lol but i will if i have too.
Im not doubting your advice in anyway and for the sake of another 3 hours it will be worth doing but im just interested in the mechanics of it all. How does this happen by the valve hitting the piston?Does the shock of the collision make the ring jump landings?
aye,no probs,the valve hitting the alloy piston can squash the alloy down onto the ring lands hences trapping them,had it a few times on engines in the workshop,
Here's a thread from a while back which may help: http://www.clubgti.com/forum/showthread.php?t=37905
Aaaah i get you now.Great stuff thanks for explaining.I will whip them out after the weekend shift. Do you have any ideas on the lapping of new valves in an old head?Some people say do,some say dont.Personally i think its better too but ive not done any major rebuild work on newer vws.Essentially they should be the same as any engine but im just anal and want to cover every angle.
You don't really need to lap them in, new valves don't get lapped into new heads at the factory. But its a good way of highlighting/getting rid of any damage to an old seat. What i'm surprised that no one has mentioned is to make 300% sure you get rid of every trace of the paste. Leave some in and you will have been far better off not lapping at all. Mike
The big question is why did the belt snap if it was all only changed in September? Something must be wrong and/or the belt was fitted incorrectly. Did the water pump get changed also? I'd be doing a thorough investigation in case it happens again in a few months!
Ive got a parts washer in my garage so it will be getting a good rinse after the grinding. Ive done 4 now so will carry on to keep the others the same. As for the reason it snapped,im stumped! When i bought it i put new hyd lifters,roller rockers,oil pump full cambelt kit etc Did it all myself as ive done plenty of cambelts in my time. Its difficult to get it wrong as all 3 tensioners have the preload needle markers you have to set them too and i know they were cock on. When i stripped it all down this time round i checked all tensioners and they were fine.The waterpump was perfect but i have changed it again anyway. The engine turns over perfect with no noise. There is no play in anything in the block at all either! It was a goodyear belt/kit bought from ECP so ive emailed them to see if they have had any problems with a paticular batch after giving them the batch code off the belt. Dreading running it up for the 1st time.