1zz-fe engine rebuild - help required

[monpey]

This is my first post on this forum, so here goes!

I have a 2001 MR2 Roadster that's been burning oil for a while now (1 litre every 100 miles!).

So, I've decided to try and repair the engine myself using a copy of Toyota's workshop manual. I've removed the engine and now have it in pieces, the question now is what's wrong with it and how do I repair it.

I've measured the cylinder bores with a bore gauge and have come up with the following diameters.

Cylinder 1 short - bottom 79.005mm top 79.015mm
Cylinder 1 long - bottom 78.995mm top 78.99mm

Cylinder 2 short - bottom 79.01mm top 79.04mm
Cylinder 2 long - bottom 79.008mm top 78.99mm

Cylinder 3 short - bottom 79.017mm top 79.044mm
Cylinder 3 long - bottom 79.013mm top 79.0mm

Cylinder 4 short - bottom 79.01mm top 79.02mm
Cylinder 4 long - bottom 79.0mm top 79.01mm

The workshop manual says that if the diameter is more than 79.013mm then you should replace the cylinder head (or get it re-bored). From the measurements taken it would seem that I need a rebore due to cylinders 2 and 3 being too wide when measured short ways across the block. However, I'm not sure if Toyota's tolerances are too stringent or not. Any advice is much appreciated.

I have also included a picture of the cylinder head which to me looks like it's had a lot of oil passing through it, especially cylinder 2. I've tried pouring petrol into the combustion chambers and they seem to hold petrol OK, so I assume the valve seats are OK. I'm guessing it needs new valve stem seals but again with my lack of experience I'm not sure. Again, any advice here will be much appreciated.



Darren

[smarty72]

Piston rings have probably gummed up and allowing oil to pass through or oval bore syndrome?

[MattPerformance]

No sure where you're getting your info from but that's not how the Toyota manual tells you to measure the bores.  Unless you have access to a 3D coordinate machine it's impossible to measure to that level of accuracy.

I'm not going to give away all of my secrets (alas, my living depends on them!) but from what you've written you seem to be quite a way out of your depth.  If you inspect the pistons and rings you will find the cause of your oil contaminated No 3 cylinder (that's No 3 cylinder, not No 2 - you count from the front timing cover).  All cylinders will be affected by the oil control ring issue although clearly No 3 is the worst.  Is the pre-cat still in place for that cylinder?  If not it will have also blocked your cat.

It's highly unlikely that there's anything wrong with the head unless there has been any overheating/ head gasket related problems.  DO NOT use aftermarket head gasket or rings, they are rubbish.  What condition is the crank in (and associated bearings)?

[monpey]

Thanks for those comments, I must admit I wasn't sure if I was looking at cylinder 2 or 3. The pre-cats are still in place with no signs of breaking up luckily, so I guess my cat is alright. Will remove the precats when I start re-installing the engine.

I've checked the crank bearings using plastigauge and the oil clearance is within the 0.028mm - 0.060mm at the widest point.

I've also measured the pistons with a micrometer which seem OK and can't see any obvious broken rings.

Darren

[Anonymous]

I would hone the bores to make them nice and round and to clear off lips etc. The rings normally gum up with carbon, burnt oil etc. So new rings from Toyota cleaning the rest of the piston. As your that far in the engine I would fit new crank bearings for what its worth so you know they good. And then a case of reasemble with new gaskets. Also one other thing and that's good on you for wanting to do it most people are normally to scared.

[monpey]

Thanks mate, I've already bought a honing tool that fits on the end of a drill. Will buy the rings and gasket set from Toyota.

Darren

[K T M Rider]

Hope it all Works out well for you.

Have a read of the thread below if you haven't already, some good info for you:


LINK:   l viewtopic.php?t=32018 l

[MattPerformance]

Thanks mate, I've already bought a honing tool that fits on the end of a drill. Will buy the rings and gasket set from Toyota.

Darren

What grade honing stones are you using?

[monpey]

Just to update everyone, I finished the engine rebuild in July and have now done 2000 miles with the engine running very well without burning oil. Cost me about £500 in parts (new rings, professional honing of cylinders, new gasket set and £500 in tools (2 torque wrenches, bore gauge, special sockets etc). So altogether a very worthwhile exercise, although it was hard work and frustrating at times and not for the faint hearted. However, I have now saved the car from being scrapped and look forward to many more happy miles motoring.

Darren

[MR2Al]

Good for you, have done a couple of rebuilds in the past when I had access to a forces motor club, not sure I would attempt it in my garage tho`. Don`t think Matt has too much cause for concern as cannot see many others attempting it in the shed at home. The feeling of satisfaction that it all works is quite good too.

Al.