Building a Built Motor

#1

I had a bearing go out in my motor this weekend. It was the original stock motor that came in the car back in 87 and has never been out of the car or had the head off. I have a spare stock motor for the car. My question is should I just put the spare motor be dropped in in stock form for $1,200 to $2,000 is what I have been quoted or totally build the motor for $4,500 installed? Are these decent prices? Please give me some input on this.

#2

Do you have any idea how many miles are on the spare?

I think I’d get compression and leak down numbers from the spare and decide where to go from there. If those numbers are decent, drop in the spare and have at it.

#3

The motor has about 120,000 on the clock. It also has been sitting out of a car for about 1-2 years. Numbers should be fine as it was pulled from a automatic one owner car. The concern I have is that without the crank scraper and updated rocker arms how long will the motor last? If I am going to do the rocker arms and crank scrapper I should just build it to the max since everything is already torn apart. At what point do you justify the power and the longjevity of a built motor vs. the stock motor and their price points?

#4

theironman9154 wrote:

When I started racing, I ran a crate motor. I waited until I had developed my driving to the point where I had better corner exit speed, but couldn’t hold the draft on the back straight at Road Atlanta. Then I went to a “pro” motor for the Miata.

That will make you learn how to be smoother, more consistent, better with the brakes.

Seems like the latest consensus is that properly adjusted valves eliminate almost all the worry about rockers. I don’t know what is involved in installing the crank scraper, but I didn’t think it was much more involved than removing the oil pan and doing a bunch of test fitting, trimming, etc. Then reinstall the oil pan.

If it were me, I would go with the spare motor if compression and leakdown numbers look good. Spend the other $3k on test days and tires.

Steve D.

#5

I agree with Steve, and would add that if the spare is good and you decide to go with it while the motor is out is a good time to do a couple things to refresh - the oil pan gasket / crank scraper, timing belt / head gasket, belts / hoses, maybe the clutch. Should serve you well for quite a while like that.

#6

I’m with Steve on running the spare motor vs having one built. When you get to the point that the motor has become the limiting factor…

While rockers have been known to break, it isn’t all that common if the valves are kept in adjustment. And even if you break one it isn’t a disaster and won’t destroy the engine, though it might ruin your weekend.

The crank scraper is very worthwhile and will extend the life of the engine. Installation is merely a matter of triming the scraper to eliminate interference with the crank. It isn’t too bad to do with the engine in the car, but it is a piece of cake to do with the engine mounted on an engine stand.

As junkyard motors go, that’s a fairly low mileage engine and will probably be in very good condition. However, since it has been sitting for a while, you might find that some of the seals will have dried out and leak. At the least, a new rear main seal should be installed. The other seals can be changed with the engine in the car, so they could be deferred. I’d change the cam seal when I installed a new timing belt while the engine was still on the stand.

#7

at this point, i’d probably check out the spare motor and use it if it’s good…i’d be very hesitant to throw any money at a built motor with all the hp/tq limits talk going on…