What is going on with my rebuilt engine?

Elan Discussions
1

Send help.

I recently mashed two engines together, one running but leaking oil so badly my friends named my Elan the Elan Valdez, and one non running, together to create one engine that hopefully does not leak oil and runs well. It’s a 4 bolt, rope-seal engine, so maybe that was wishful thinking.

Anyways, I took the old cylinder head from the running engine and put it on a rebuilt block and crankshaft from the non-running engine. The old head has its problems - totally clapped valve guides - but unfortunately I had no time to fix that and money was also getting tight.

The old block was not bored oversize - the bores were checked for taper and ovality and found to be almost pristine, so they were just honed. The rods and pistons were reused as well but the piston rings were replaced. Piston to ring gap was on the upper edge of acceptable but still within limits. The crankshaft was reground -.010" on the main and rod journals.

After much rending of garments and gnashing of teeth over the past 3 days, I started the engine up today. I let it run between 2k and 3k rpm for about 10 minutes, and it was smoking quite badly, but I took it down the road. I did some acceleration cycles in third gear - start at 2k rpm, accelerate moderately quickly to 3.5k, then brake or coast back down to 2k. Lather, rinse, repeat for about 15 minutes. I noticed two problems: the large cloud of blueish-white smoke that was present whenever I put my foot on the gas pedal, and the fact that the engine sputtered and had almost no power if I floored it.

After about 15 minutes, a dead miss suddenly developed. It was present at all RPMs, no matter what I was doing. If I called for acceleration, it was noticeably missing on what I perceive to be one cylinder.

I arrived at my girlfriend’s house (it was closer to my location at that point), distraught. So far I have pulled the cam cover and the spark plugs. All 4 plugs are black and I’m guessing that’s from burning oil. Cam timing is spot on. Compression readings, as taken with the engine warm after the engine had been sitting for a couple of hours are:

Cylinder 1: 100
Cylinder 2: 110
Cylinder 3: 115
Cylinder 4: 110

Any and all help is appreciated. As I conduct further testing I will post updated information.

Thanks,
Ben Morris

2

Hello Benny,

Some places to check:

The compression is very, very low, to the point of a very worn motor despite the new rings. Compression on a fresh standard engine is around 190PSIG. If the ring lands are very tapered and you have wide ring gaps, that will be hard to seal to the cylinder walls. The oil control ring gaps should be 120 degrees apart at assembly. Compression rings should also be away from each other, away from the wrist pins.

Worn valve guides aren’t good, but did you have the valves and seats ground and lapped in at all?

I feel your frustration. I had to rebuild my motor years ago with barely two nickels to rub together.

Regards,
Dan Wise

3

I did pay careful attention to ring orientation during assembly, so I don?t think that is the problem. The ring-to-land clearance was near the upper limit of the acceptable range - a fact that I?m attributing to the pistons being used for racing at a point and thus having the ring lands well smashed.

The seats were not ground or lapped when I swapped the head over. The only thing that I did was swap a shim on E-1 because the clearance was too tight at .004?. The intake seats would have needed to be replaced rather than reground - all intake shims were .060?, plus or minus a few thou.

I worry that I have become the butt end of the saying of ?a penny saved and a pound foolish.?

4

Don’t worry too much about the absolute compression readings. It’s a function of many variables. At least they are even. Did you inject oil into the cylinders and do the compression test again to see if they improve significantly?

5

throttles fully open during the compression test?

6

Oil burning on acceleration, plug fouling and low compression pressure all suggests the ring performance ( both compression and oil rings ) was not good enough on initial build and has not rapidly improved as it should on the initial run to bed the rings.

If your lucky further ring bedding runs will result in acceptable ring bedding and increase in compression pressure and reduction in oil burning or maybe it will not. If not then the rebuild of borers, pistons and rings was not adequate and needs to be completed again with closer attention to dimensions and tolerances and what is acceptable and not.

regards
Rohan

7

I was under the impression that smoke on acceleration was valve guides; smoke on decelleration was rings.
Valve stems were said to be iffy and perhaps heavily oiled rings not bedding? I’m no expert but I’d do the head and try again.

8

What oil did you use to “bed in” the new rings? I always use a stright SAE40 grade for breaking in the rings then change to a multi grade 20/50 after a couple of hundred miles, these modern oils (synthetic and semi synthetic oils) are just too good and dont allow the rings to bed in (IMHO)… others may have have a different opinion on the matter.
…

9

I agree. I use running in oil sold by Penrite here in Australia which is a SAE 40 mineral oil with a specific additive package to aid bedding in of engine components.

cheers
Rohan

10

Checked your ignition timing as well? That can cause fouling if it’s way out (ask me how I know :open_mouth: )

11

Worn inlet guides produce smoke under high manifold vacuum conditions such as over run or idle. Worn compression rings or non bedded in rings usually produce smoke under load as the high blow by volumes passed the compression rings stop the oil rings working properly. Worn. faulty or not bedded in oil rings may produce smoke in all circumstances

why new rings may not bed in properly is a complex multi faceted problem some of the potential issues have been highlighted e.g. running in oil used, ring land wear. installation and ring gap plus many others such as quality of bore honing, running in procedures, piston and bore wear within nominal tolerances for new components, quality of the rings themselves.

cheers
Rohan

12

Yes quality of bore honing is critical. The cross hatch angle and depth of hone are difficult to control unless it’s done properly by machine.

13

This is a jolly read… and may even help with diagnosis of the problem.

memoparts.com/img/cms/Docum … Failue.pdf

Jeremy

14

Yes. The practical method is to coast down a long hill. When you open the throttle at the bottom, you will see a smoke screen for bad guides. Bad rings will be providing a consisent level of smoke regardless of manifold vacuum (throttle position).

BMW used to recommend DRY assembly of rings, then startup and holding at 3,000 RPM for a full minute. After which the rings were supposed to be bedded.

Sounds harsh, but back then (1968 for me), they made quality cars and motorcycles.

15

All,

Thanks for your replies and insights.

I am now in Florida and the car is in New York. I am going to pay to have it shipped down here and then I’ll go about removing the engine again.

I’m going to pull out all the stops and just do it right this time - what I should have done the first time. I’m going to replace the pistons, rings, wrist pins, small end bushings, and also take the block out to +.020". The cylinder head will also have its guides, valves, and intake seats replaced.

Since I have to tear it all apart again I’m debating spending more money and going all-out in case I decide that at some point in the future I want to put a really high performance head on this block. If I put in steel main caps, I assume that they will need to be line-bored to suit the engine. If that is the case then will I also need to get the special oversize bearings that are made for an engine that has been line-bored?

16

You don’t need upgraded main bearing caps unless your block is earlier production with the rounded type caps (120E, 2731E, 681F). These days the cap mounting face on the block is typically ground down very slightly prior to line boring with the cap in place in order to avoid the need to fit bearings with oversize OD. This moves the crank centreline a couple of thou toward the cylinder head deck surface.

17

You can line bore with new steel caps for the standard bearing shell O/D

regards
Rohan

18

Yes, the block is a 120E with the rounded caps. Good to know about the line boring, thanks.