Changing the 4g63 from an Interference to a Non Interference

[stoffdog01]

hey, i just recently found out that i have to replace all the valves on my newly rebuilt engine . Has anyone ever thought of fly cutting the pistons so that they no longer hit the valves in the instance that the timing belt slips of breaks?? I dont know about you all, but i get tired of hearing about people having to replace their head a number of times during the time they own their DSM. I know people do this in flat top pistons so that they can run higher lift cams, but im not sure if it is possible to do with the dished turbo pistons. Let me know what you guys think, or if anyone has done this.

Thanks, Tim

 

[project_tsi]

Do your timing right, then you won't have to replace your valves.

But I don't see it happening.

 

[blue1]

Its possible just work out your piston to valve clearence on overlap then add the rest of your total lift add approx .030. then see how much you are going to flycut from the piston. Best to do this with an old piston first then cut the piston in half through the flycut and see how much is left near the backside of the top ring groove before it is going to break through. Then CC the top of the piston to see how much compression you are going to loose (better do this before you cut the piston in half) then weigh it all up against the cost of double checking when you first put you engine together and regular timing belt changes.

 

[stoffdog01]

Do you know what the standard piston to valve clearance over lap is? Or do you know where i could find information on this? Thanks for the reply
Tim

 

[Big Woo]

To me I do not see the point. If your willing to take the time and spend the money required to customise the necessary engine internals , to eliminate any chance of the valves and pistons making contact with each other. Then you must already have the resources to assemble or pay someone else to assemble the engine correctly, so that this does not happen. Or do you just want to drive your car without fear of the timing belt breaking, eventhough you know you should have replaced it 10,000 miles ago.

I'm sorry I just do not see any need to spend time or resources on something that is a non-issue if proper assembly techniques and and periodic maintenance is preformed.

 

[Big Woo]

Standard piston to valve clearence depends on a multitude of things. Such as cam profile, piston height, piston relief, valve diameter, rod length, valve seat depth, valve timing, and many others. In short the only true way to know is to assemble and measure your specific combonation of parts.

 

[SpoOLxExO]

Besides, if your Belt looses teeth at the crank, and some of your valves are fully open theres no amount of fly-cutting you can do pryor to digging into the wristpin area that will prevent this.

You are basically asking what it takes to completely re-engineer an engine design that works just for kicks?

These guys already made several great reasons to why this procedure appears pointless.

 

[Enraged78]

The best way to keep from bending valves is just basic care for your DSM.

With that being said, it would be far cheaper and easier to build up a 4G37 and swap it into your car if you're that worried about it. The 4G37 is the SOHC Non-interferance 1.8 liter 8-valve motor out of some of the 90-94 T/E/L's. The 4G37 can be built for some power, and is a great deal simpler than the 4G63. Boring it out can alleviate some of the displacement loss that it suffers compared to the 63, some head work can help the flow get closer to the 63's head, and forged pistons could help it handle boost. However, whatever way you decided to cut it, It would still be an 8 valve motor, and would not be worth it compared to what you have now. If you've got money burning a hole in your pocket, and you REALLY don't want to change your timing belt when you should, this is a viable option.

Bending your valves sucks, but it's not worth reinventing the wheel over. Especially when the cons outweigh the pros.

Matt.