Carbon on cylinder walls - normal?

[Paul_D]

Hi,

I'm new to 4-cyl engines and would like to get the experts' opinion on something. The photos are of a 914 2.0L race engine. I'm in the process of buying a car, and the engine failed a leak-down test with intake leaks on cyls 1 & 2. The seller has pulled the heads for repair, and sent me these photos of the pistons & cylinders.

What looks strange to me is the apparent carbon build-up on the swept portion of the cylinder walls. Generally, on engines I've worked on, the rings keep cylinder walls pretty spic & span no matter how much build up is on the top of the piston. Does this indicate worn-out rings? Excessive piston clearance? Anything else?

Thanks in advance for any advice.

Paul
Ojai CA

'71 911T
'71 914/6
'74 914 ?

[John Rogers]

Well as far as I can remember, with a race engine all the normal things may or may not apply. You have to take into account what cam was used and how radical was the valve timing, what sort of advance was in the distributor, what fuel was used possibly leaded, what was the compression ratio of the engine and finally how much time on the engine? It is possible that the ring joints happened to line up and with 12:1 compression or something crazy like that would blow right on down the cylinder walls. I would ask what sort of power the engine made on the dyno and try to get answers to the things I noted above which will give a better idea of how it will last in the future. I would measure everything before making any decisions on what to do and then proceed.

Back when HSR-West had the Porsche 2L series going full bore, some of the really hot 2L fours would last maybe 2 race weekends and then need an overhaul as they were built so loose and run so hard. You also have to remember that a type four "race engine" is not what they were ever initially designed to be used for so they will be very high maintenance.

[Paul_D]

Thanks John,

The claims are:
the engine has about 20 hours on it.
10.5:1 compression, J&E pistons, full race cam.
The motor hasn't been dyno'd but according to seller similar engines he's built make around 150.

It seemed to me that at a minimum we shoud have him pull the cylinders, get some measurements, if OK then re-ring, hone, and put back together with freshened heads. If numbers are nnot OK, the new P/Cs.

Do the bottom ends tend to hold up? Is it asking for catastrophe to just do a top end job?

THanks

-Paul

[Joe Ricard]

I think the cylinders are worn out.
But not leaking too much around the head sealing surface.

It's rebuildable for sure.

[Paul_D]

Thanks Joe. Any recommendation for a race piston/cylinder set for a 10.5:1 engine? I'm not expecting to set any lap records, nor do I want to rebuild a motor every 2 races. But I would like to be able to keep the rest of the pack in sight, if you know what I mean.

-Paul

[John Rogers]

For an engine with 20 hours on it, it appears to be a mess and looks like it was never cleaned or well taken care of. If you buy it I would plan on a full tear down and full set of measurements taken to see what you have and what will be needed. When you said "full race cam" I would be really suspect unless you can get the specs and look closely at the cam lobes and lifters as it may have been sleeved for type 1 lifters, etc.

[Joe Ricard]

There is no such thing as a "full race cam". I read this as Bull ****. Cams are identified as John said. Lift and duration of intake and exhaust lobe @ .050 Lift. and Max lift.
Might be a good idea to pass on this engine and build something yourself.

[John Rogers]

As I noted, a close inspection is very warranted and possibly an expert brought in. As an example, in 2002 I had the chance to buy a type 4 engine that was stretched out to 2.8L and had "lots" of racing stuff done to it. It was together but had never been run so I had my race support shop, Black Forest in San Diego check it out since the price of $6,000 seemed like a lot for me to spend at the time. The cam was a really radical Crower off road type of cam with titanium push rods, type 1 ceramic lifters, Pauter 78mm crank, Pauter long roller rockers and a set of rewelded and flowed heads worth about $10K all by themselves! They said to go for it which I did and it made 190HP at the rear wheels in a slightly de-tunned mode and ran for several years before blowing a rod in two. So as you can see, you will have to look closely to see what is really there and I would suggest some help if possible.

[Paul_D]

Thanks for all the input. You guys are great.

I spoke with the seller - who also built the engine - and he convinced me that what looks like carbon and burned oil on the cylinder walls is actually a reflection of the the tops of the pistons. The cylinder bores, he insists are absolutely clean, smooth and very shiny. The more I studied those pictures, the more I can see that he's probably correct.

The engine IS filthy, and it may have more time on it than stated, and the rest of the car is rough. But I think the price reflects this. Incidentally, the car was listed on Pelican classifieds, and some of you may know the car and Steve, its owner:

1974 Porsche 914-4 racecar for sale $6500.00

The deal on the car is not consummated, and this isn't about haggling over price. It's a completely amicable transaction so far. I just want to try to foresee any serious trouble, and deal with it now while the engine is out and the heads are off. We're going to have him go ahead and pull the jugs, get some numbers, and at a minimum, give a light hone and new rings. If pistons or bores are out of tolerance, then we'll deal with them too.

Thanks again for the assistance.

-Paul