Doing my HG tomorrow..

[babyfacefitz]

A friend of mine who is a mechanic at the stealership is doing my HG on my 98 OBW with 220K on it. The temperature never spike till the last day. It never went over full tilt but got high up there for just a bit.

 

When I check my warpage, would a new level from home depot work?

 

What's the chances I need the heads resurfaced? He says most at the shop don't need it.

 

thanks.

Michael

[nipper]

So right away I am going to tell you let a machine shop decide if they need it or not. I would NEVER skip this step, as it is not only warpage but surface finish. You dont use a level from home depot, you need a high quality steel straight edge and some feeler gauges to do it at home.

Most who skip this step have to do it all over again in a short time.

 

At over 200K Personally I think it is foolish to do HG's without a compression test first. Even then I wouldnt do it. Odds are the restored compression with well worn rings will cause blowby and oil burning. My cutoff for sooby engines is 160K.

[idosubaru]

Don't bother trying to check flatness yourself.

 

A machine shop should be doing the head surface but i've successfully skipped the step a few times for various reasons and none have come back to haunt me. Actually the first one I ever did like that was years ago and the owner is a board member still driving the car.

 

Subaru is known to skip the step as well.

[GeneralDisorder]

You can't check for warpage without a ground machinists straight edge.

 

Chances are good that if it is actually checked by a machine shop they will say to resurface it. The spec is far lower than is actually tollerable in real life, and also the resurfacing is done as much to provide the proper surface finish as it is to remove warpage.

 

With proper cleaning it is highly unlikely that you would have a problem just reinstalling them

 

It is also pretty easy to resurface them yourself with a thick peice of glass, some wet/dry paper and WD40. That is also the only way to check for warpage without a straight edge. I've done heads this way and it takes an hour or so per head but the results are very nice and it's very controllable from a surface finish perspective. Though I'm sure you aren't into measuring RA and such.

 

GD

[The Dude]

So right away I am going to tell you let a machine shop decide if they need it or not. I would NEVER skip this step, as it is not only warpage but surface finish. You dont use a level from home depot, you need a high quality steel straight edge and some feeler gauges to do it at home.

Most who skip this step have to do it all over again in a short time.

 

At over 200K Personally I think it is foolish to do HG's without a compression test first. Even then I wouldnt do it. Odds are the restored compression with well worn rings will cause blowby and oil burning. My cutoff for sooby engines is 160K.

 

So, are you saying just junk the old engine and install a replacement? Replacing blown head gaskets would only restore the compression to a level normal for a used engine. It's not like doing a ring and valve job on a high mileage engine where the compression is restored to new engine levels and the rest of the engine can't take the strain.

With a little luck, a Subaru engine is good for 300,000 miles. I would invest a head gasket replacement in an egine with only 160K. Replacing an engine is a risky propostion as well. It seems way too easy to get burnt badly on a rebuilt or JDM engine to give up on a 160K engine with a blown head gasket.

[logic23]

Nipper, You wouldn't do headgaskets on an engine with over 160k or you wouldn't use an engine with over 160k?

As far as doing headgaskets on your 2.5 DOHC just junk the engine and replace it with a used 2.2 sohc engine. There are 100's of posts on here about it but it will take you down a much happier path with your car.

[nipper]

Nipper, You wouldn't do headgaskets on an engine with over 160k or you wouldn't use an engine with over 160k?

As far as doing headgaskets on your 2.5 DOHC just junk the engine and replace it with a used 2.2 sohc engine. There are 100's of posts on here about it but it will take you down a much happier path with your car.

 

 

I wouldnt do either. There are plenty of lower mileage engines out there. You can take a chance, as there is always one or two that say it doesnt matter, but if you want to keep the car for any length of time I would not do it. For the amount of work that is about to go into this, you can do an engine R and R and timing belt and seals and plugs, which all would be done with the HG job anyway.

 

Now if all you can find are engines that avg around the same mileage used I would go with one of those.

 

If you decide to go with the HG, you should also get a valve job. This job skipping any step will come back and bite you in the tuchus.

[logic23]

This is a side note to this post but....

Nipper, can you tell the aproximate mileage on the engine from wear on the cylinder walls. I have only taken engines apart that are around 100K and the cross hatching in the cylinders looks great. In addition there is no lip at the end of the cylinder. I have taken apart a couple engines that I didn't know the mileage and their cylinder walls were perfect too. Any thoughts? Am I just looking at lower mileage engines or do subaru engines show little wear in their cylinder walls etc.?

[nipper]

This is a side note to this post but....

Nipper, can you tell the aproximate mileage on the engine from wear on the cylinder walls. I have only taken engines apart that are around 100K and the cross hatching in the cylinders looks great. In addition there is no lip at the end of the cylinder. I have taken apart a couple engines that I didn't know the mileage and their cylinder walls were perfect too. Any thoughts? Am I just looking at lower mileage engines or do subaru engines show little wear in their cylinder walls etc.?

 

A Well maintained engine will have the original cross hatching. It means it had regular oil changes, never overheated, and no mechanical damage. Opposed engines are good at lasting since the opposed forces all cancle eachother out. The rings however 200K is 200K on thin peices of metal going through a little bit of hell everytime there is a boom. On a subaru I wouldnt be afraid of a 100K engine.

[GeneralDisorder]

I wouldn't be afraid to do HG's on something with higher mileage. I've done HG's on stuff with 250k+ without issue. I won't do a valve job as that will definitely increase cylinder pressure's but a lot of Subaru engines are still in great shape at 200k+ so I see no problem with replacing $75 worth of gaskets.

 

EJ25D's being a possible exception. They are known for bottom end fail if they have been overheated a bunch prior to the HG's so mileage is a consideration - it's always a gamble with that engine it seems regardless of mileage.

 

As far as ring/cylinder wear goes - rod bearings will claim the engine long before you see any significant were on the cylinders. Just the nature of boxer's and how well they retain oil around the piston due to the cylinder orientation. It doesn't drain away effectively when the engine is stopped so it eases startup loads.

 

GD

Edited July 3, 2010 by GeneralDisorder

[nipper]

I am assuming we are talking 2.5's as I have a diff opinion on 2.2's.

 

No matter what you do, after an overheat an oil change is very important. Before you really dig into taking anything apart, remove the radiator and flush it immediatly. If you leze it exposed to air, with antifreeze, a smattering of oil and goo from combustion, it will all turn to glue and clog the radiator. Just give it a good rinse.

[eppoh]

Do not waste your time on a high mileage, overheated engine head job without checking and resurfacing the heads- unless you want to do it twice.

 

It is not that expensive. Not doing it is sorta like unprotected sex with a hooker. Feels good for short time, but what happens later?

 

If you really can't afford the machine shop charges, go to a glass shop and buy a glass jalousie and use that to check the heads. I did that once with an outboard motor on a dockside rebuild. Worked out okay.

[GeneralDisorder]

I use a 3/8" thick peice of plate glass backed with a 3/4" thick peice of plywood and held in place with nails driven into a solid wood bence. I start with 120 grit, then finish with 180 grit. Use wet/dry paper, lots of WD40 and do figure-8's with the head. You have to rinse off the paper frequently with WD40 - don't use any solvents as it will destroy the paper.

 

It actually works quite well. I know machine shops that use big belt sanders to refinish heads - same thing going on there.

 

There's many ways to skin that cat and you don't have to pay for machine work if you don't want to. A few supplies and some injenuity will suffice.

 

GD