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Hello everyone, i own a bigport 4age that needs the valves to be readjusted,, today i measured the valve clearances and all were pretty much way off the mark. A trusted friend said i should send in the head to have the valves re seated and for new shims.. Would this be the most effective way to approach the situation (cost, quality)? Or should i just sell the head on ebay or something and buy a re manufactured head online..? or perhaps just purchase new shims and not worry about the rest?

Thanks in advance,

Thor
 

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Dude,

I would only feel comfortable having the cylinder head that's on the engine rebuilt rather than trusting a randomly sourced head from an unknown online company. Obviously I would only want a local machine shop with direct experience with the 4age engine to work on the head. The internet is good for a lot of things; top-quality engine work is not one of them.



- Chester
 

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Discussion Starter #3
I see. if i was to send it into a local machine shop, what should i have them do? just the re seating and shims? by the way, can they calculate the shims i need with the head off of the car or should i give them the readings i have measured? I assume id have to give them the head with the camshafts still attached..?

Thor
 

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I see. if i was to send it into a local machine shop, what should i have them do? just the re seating and shims? by the way, can they calculate the shims i need with the head off of the car or should i give them the readings i have measured? I assume id have to give them the head with the camshafts still attached..?

Thor


Dude,


Normally you would take a cylinder head to a machine shop for a standard 'rebuild'. This means it's stripped, cleaned, pressure-tested, and valves are checked for wear. The brass guides would normally be replaced and a 3-way angle grind/cut for the new seats is then performed. The head is checked for flatness and possibly 'cut' (resurfaced) if found out of specification. After further measurements ensure the valve clearances are correct, final re-assembly occurs, at which point the shims are installed. There is no point in giving them any measurements since everything will change during the rebuild process. To remove the head you'll have to remove the camshafts first as I recall. You might as well have them check your camshaft for wear on the lobes and other possible issues. Check with them first.


Here's a link for a general head rebuild (not 4age-specific) that explains things in further detail.

http://www.hotrod.com/howto/51058_cylinder_head_rebuild/

The 'average' cost of a good quality cylinder head rebuild in my area (San Francisco Bay Area) is $350 for a 'standard' rebuild to factory stock condition. Take that value with a grain of salt.




- Chester
 

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If it is just your valves out of spec and this is just a daily driver I would do just that, readjust the valves.
It takes a good bit of effort to pull the head from the engine when its fully dressed in the car.
Machine work isn't cheap. It all determines on how much you want to spend and what your plans are for the car.

If you take it to be machined you have to pull the intake, exhaust, timing belt, cam shafts, distro, get all new seals and gasket etc... it all adds up quick and if you don't have any experience with the sort of thing it can be a pain.

I wouldn't bother selling the head, you would just have to turn around and spend more to get another and be in the same place.

You can determine what shims you need by measuring your current clearance and recording how much you need to get them back in spec. Them measure the shims themselves and add or subtract the difference and that would be your target shim. Its all in the BGB and there is a little formula for it.
 

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I see. if i was to send it into a local machine shop, what should i have them do? just the re seating and shims? by the way, can they calculate the shims i need with the head off of the car or should i give them the readings i have measured? I assume id have to give them the head with the camshafts still attached..?

Thor
By reseating do you mean lapping?
If so then this is not what you want to do.

If your valves are leaking or otherwise damaged they need to be ground or replaced.
If you were to do this on your own I might suggest lightly hitting the valves with a very quick lap to confirm contact area but if the contact area is not acceptable then you would be better off getting them ground instead of trying to lap them back to an acceptable state. Lapping leaves a much less ideal contact area.

If there are no signs of bad valves such as low compression I would do exactly as suggested and just reshim the valves. You could take the car to a shop to have them do this. I would guess they would charge a couple hours to do this which can add up.
Or you could do it yourself. You need a very basic tool kit a small micrometer and feeler gauges. You will also need shims. These are pretty easy to source. There was a thread on this just a couple days ago. Pretty sure it was here but may have been on mr2.com.
It sounds like you are pretty new to things so it may take a little longer but if you had a batch of shims on hand you could probably do it in a short day.
The other option is to measure your gap, pull the shims and measure them then you see if you can mix and match the shims you have to get as many valves in spec as possible, find out what new shims you need and then get/order them. Once the new shims come in you swap them in check everything and if it looks good you button it all back up. This method does involve your car being down while you do it but still it would be faster than shipping your head somewhere to get done so it doesn't sound like downtime is the hugest concern.
 

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Hello everyone, i own a bigport 4age that needs the valves to be readjusted,, today i measured the valve clearances and all were pretty much way off the mark. A trusted friend said i should send in the head to have the valves re seated and for new shims.. Would this be the most effective way to approach the situation (cost, quality)? Or should i just sell the head on ebay or something and buy a re manufactured head online..? or perhaps just purchase new shims and not worry about the rest?

Thanks in advance,

Thor

What clearances did you come up with?? Do you still have the numbers recorded?

TYPICALLY valves don't get looser in a 4AG head.... once clearances are set they typically don't change. How long have you had your MR2?

It is possible that a PO was/is responsible for loose clearances... and other anomalies
 

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Discussion Starter #9
Well the engine is already mostly disassembled.. Im pretty comfortable with taking most of the components you listed off the car maybe with the exception of the camshaft and timing belts.. But I do have a Haynes manual so I should be fine. I'd like to do it right and have the head ported at the same time as well..
 

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Discussion Starter #10
I do have the numbers recorded still and they are all out of spec except 1 or 2 valves. And yes this is due to the previous owner rebuilding the bottom end of the engine (new piston rings, bearings and gaskets.) I figure I might as well finish off the job and get the head rebuilt and ported. Any thoughts on porting the head anyone? Pros and con's?
 
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