Discussion
A work colleague has spoken to me today about his re-build VR6 engine going into his mk2 golf,first he needs to build the engine.He had a 2.8 engine rebored to 2.9,by a reputable firm locally and honed.The pistons were a set from a 15k engine and show no signs of wear other than a slight scuffing on the skirts.The main pistons have no signs of wear and have all the rim lines still there.He has put a new set of rings on them.He is worried about bore to piston gap and says there is a bit.I say there is no worries for the gap,as the pistons will expand slightly(I've not seen the gap,but on other engine builds I have done there is a gap).More importantly he needs to gap the rings correctly.Can anyone confirm that there is a gap ( I know I have no technical measurements) although with a fresh bore and hardly used pistons and anyone know a ring gap for the VR6? thanks p.s he maybe putting a low pressure turbo and a compression plate on it for next years project,would that affect the gap too.
The question really has to be, how much did they overbore the cylinders? I need to know this. More then a few thou could mean rattling when cold etc plus his ring gaps will be huge. This could be a goofed job imo but lets hear how much the overbore is. Ring gaps vary according to application and the ring position on the piston. There are SAE guidlines he can look at. He may be in the ballpark if he's boosting but for an atmo engine it's going to be a tad unhealthy.
Boosted.
Boosted.
He got 2 engines to build one.One was a 2.8 and the other was a 2.9.The 2.9 had oil starvation probs on the crank,so decided to use the 2.8,but needed a rebore,hence the piston swop.The company who did the rebore are a very reputable company in Reading,I wouldn't use any of the others myself.I 'think' he is looking at the gap and thinking there should be none.I am going to pop over soon to look for myself.Tech info is not that popular for the VR6.I know he's a vw head,so maybe he could get some help on ring gaps on those sites.Thanks for your answers guys.
stevesingo said:
Am I correct in saying it has been rebored to 2.9 and he is fitting a set of used 2.9 pistons. If so then yes there should be a gap. There will also be a correct specification for the ring gap, so you should find this and make a comparison. Try a Haynes book or the dealer.
HTH
Steve
This post isn't making a lot of sense. Is he worried about piston to bore clearance or piston ring gap?
He needs to have a piston to bore clearance, so the pistons don't seize, maybe .001" but I'm guessing, not knowing about corrado pistons.
He definately needs to have the correct piston ring gaps, otherwise if they butt up when hot and expanded he'll soon have bore wear problems.
So, could you clarify what his problem is or is a manual available to him? This will supply the correct specifications.
Boosted.
He needs to have a piston to bore clearance, so the pistons don't seize, maybe .001" but I'm guessing, not knowing about corrado pistons.
He definately needs to have the correct piston ring gaps, otherwise if they butt up when hot and expanded he'll soon have bore wear problems.
So, could you clarify what his problem is or is a manual available to him? This will supply the correct specifications.
Boosted.
Justin S said:
Sorry Boosted.He has an issue with the bore to piston clearance (but he's never built and engine before,so doesn't know what gap to expect).I'm more worried about his ring gap being incorrect and as you say,wearing the bores and breaking them on expansion.
He needs to find a build manual to get the correct measurements or post for info on a VR6 related site. If you gave me the bore diameter I could give you 'safe' SAE ring gaps. As for piston to bore clearance I'd say .001" would be ok but really this should be checked via a workshop manual. How's he intending to measure the piston to bore gap?
Boosted.
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