tronic

hi,

i want to do a SOHC to DOHC head swap on my 1990 mazda protege....

was wondering where i could buy a relatively good conditioned head. also what other items would i need for the conversion process (ecu? timing belt? etc.).

If anyone can help thanks!

Maz94Protege

do a search...topic been discussed!!

tronic

i already read the previous topic discussed... the sohc > dohc head swap was just talked about but no information on where to get one.

zenilder

It will be hard to find a head in good condition. I warry a head from any kind of u-pull-it yard. The engines tend to sit there in the rain (some cover the engines, but they still sit there on the ground and are exposed to the humidity). The only place I would recommend buying a head from is mazda recycler. When you order a head from them, be very specific in which head you want to buy. If you say DOHC, they'll get it right. Unfortunately, I had the misfortune of them fuxin up an order I placed for a SOHC. They sent me a f'n 8-valve head when I needed a 16-valve head. I was rather upset to say the least.

Anyhow... If you buy one from a yard, get it rebuilt, and if the shop can replace the valve guides, do it. Heads that just sit there -will- develop rust, unless the yard actually takes the time to prepare an engine to sit for a long period of time. You can expect one side of the valves (exhuast or intake, I forget which ones I saw were rusted when I went looking for a head) to have a bit of rust or a hella lot. You can also expect the valve seats to be pitted from the rust and exposure to the elements (I had to lap the valves good in the head I finally picked up). You also should replace the valve seals at the least if you choose not to do anything else to the head. The seals have a tendency to dry up when sitting in the heat out in the yards. The seals aren't that much to buy, but it does require a bit of work to replace considering you need to take off the valve spring retainers to get at them. If you don't already have the tool, you'll have to buy/rent a valve spring compressor.

Also, you'd be wise to take the head to a machine shop and have them resurface the head. Most commonly, the guys at the yard (with mazda recycler being the exception) don't know how to take a head off properly to avoid having the head warp. After they resurface it, have them either dye test the head or magnaflux tested for cracks. That's one thing, if you do pick up one from a yard, bring some degreaser and brake cleaner with you so you can test for cracks yourself. Look around the valve seats for cracks, as this is where cracks commonly form. Most yards have a policy that if you take it to a shop and it turns out that there is a crack, they'll give you your money back. If they don't have this policy, don't buy from them.

As for the parts that you will need after the swap:
-water pump from a DOHC engine (so grab that while you're getting the head. check for rust on these puppies, too)
-oil cooler (sits inbetween block and oil filter, you'll need this to have the water hoses fit properly, otherwise you're on your own to get custom fitted water hoses)
-water hoses from DOHC
-DOHC timing belt
-DOHC timing belt cover (not a necessity)
-Distributor (most likely. I haven't taken the time to see if my SOHC dizzy will fit on the DOHC)
-DOHC Intake manifold (sohc doesn't have VICS)
-DOHC exhaust manifold (bolt pattern is different)
-DOHC ECU and wiring harness

Hope this helps.

suprastylin23

i was interested in doing this swap also. so i went to a japanese engine shop thinking they would have the cheapest most reliable part other than a dealer. well the lady there wouldnt even sell me the head she said it was waste of money and i regret real bad. and she wont do that to customer. so she wanted to sell me a whole bp engine from japan for $995 "on special under 40,000 miles"- haha. only reason i laugh at that is my brother payed the same price for his 7MGT JDM motor for his supra. anyway she said depending on how many miles you have on your block that wouldnt be a good idea. sorry for rambling.

zenilder

Those engines are rarely under 40k miles. :\
They are usually over 50k.
For that price, you can pick up a BPT from turboge on this board.
I think I picked up my head for under $120. Should be about the same price for a DOHC. I really don't see how 100k+ miles could be bad for a head swap, provided the engine was maintained properly throughout it's life. In the long run, for someone that knows his/her mechanics, doing a head swap most likely will be cheaper than buying a complete engine. Also, for someone that might not have an engine hoist, the head swap would be a more feasable project. On the other had, if the person was going to have a shop do the work, there would be less labor involved in an engine swap, and thus would probably be cheaper.

oregano

i didn't know the DOHC head fits right onto the old bottom end. thats pretty cool. tell me how everything goes.

oregano

the reason they are selling it is prolly cuz they didn't maintain it right, and they know jack all bout cars.

94dxpro

Someone should gather all the parts needed and sell a whole conversion kit like corksport or racing beat cause it is hard where i live to find good mazda parts.

zenilder

Yes. All BP blocks are the same. Different cars and models simply use different heads. The Pro DX, Pro LX and Miata all have different heads. The DX has either of the SOHC heads, the LX has the Dual, and the Miata has a completely different DOHC head. All have the same block. Actually, they have another distinquishment between each--pistons. You can search on the forum to find more information regarding that matter.
Other than the pistons, some engines had two-piece oil pans. I'm not sure which cars/models had the different oil pan.

So if you're looking for parts, you now know where you can find interchangable parts from.