Compressionate Behaviour

[martynharrison]

Ok, I've not tampered with the timing yet, as it seems "all right" within some parameters. Barks well, isn't too smooth at tickover.

 

I did go through the ignition though, found a loose plug on the driver's corner and decided to put new plugs in as the ones it has could be any age for all I know.

 

As recommended, I've put in NGK sommat 5 and they're working ok, not sure if they have any real effect but the sense of something not producing all the cylinders has gone away a bit.

 

While at it, I removed all plugs and did a compression test on all cylinders.

 

I expected to find one or two with problems but in actual fact, I had 119, 121, 123, 125, 128 and the other three at 129 PSI, as best as I could read the gauge. This doesn't seem too bad to me.

 

Method was with plugs removed, to turn over the engine on the starter and see what the tester gauge said. First stab, a brief turn of the key got me 108 and a second go, 110, I moved onto the next and got 88, then 100. This made me try leaving the starter on for a burst rather than a stab, and the compression then followed a pattern:

 

burst / stutter / burst / stutter / burst and left like this the PSI would stay pretty much the same from then on.

 

First question would be whether this is a valid way to measure compression and if these figures are about normal or not.

 

Second question is whether the "stutter" which was hitting about every third of a second very approximately, tells me (as I suspect) that the flywheel ring gear has some chewed bit and this is why I sometimes get uncertain and unconvincing starter liveliness.

 

If yer still reading this far down, I can move on to a third question, I get good urge overtaking up hills in third (not surprisingly) but about 4300 to 4700 rpm or thereabouts, when my Scorpio would just keep pulling earnestly enough, the v8 begins to stutter and thrash. I believe this also results in copious oil smoke. I can change up to 4th or so and still overtake from 3500 up to the 4500 ish so usually change up around 4500.

 

I had thought this down to blowby and crankcase pressure building up, particularly as it did it much worse on the JWR manifold that I replaced with a 360 and when I left the pepper pots off it breathed / revved much better. IT seemed to be ok too, to some extent, with the dual pepperpot and hoses I have connected up, but there's still something choking it at 4500 by the feel of it.

 

Are the compression behaviours above good enough to rule out blowby / crankcase pressure, or maybe do they imply it? If ruled out, what else might be happening? Any ideas?

[Cinnobar]

Martyn, plugs are probably BP5ES which is correct spec for most of the RV8s. I tend to run BP6ES but suspect I might get fouling occasionally when on light throttle, especially since the carb hasn't been set up.

Compression test should be done with the throttle wide open and doing 2 tests per pot one without & one with a drop of oil down the bores to seal the rings. Your does sound down a bit and I suspect it would be bore/ring wear given the smoking you talk of. I'd expect 150+ on an SD1. High revs stutter smells of being ignition, say plug leads or cap.

 

Jim

[Guest ajttriumph]

Gee Martyn its hard to know where to start, what clour were the tips of the old spark plugs? Brown, Black or some combination.

 

Copious smoke at revs would indicate worn or broken rings (broken rings may give you the noise that you talked about) or oil rings damaged due to excessive heat.

 

Other than that what sort of exhaust have you got a small system can limit revs on rover engines.

[martynharrison]

Ok, so 120 - 130 is low, that's confirmed my initial suspicions about the blowby. Old plugs look fine, insulation grey/white, surround is coke, the bits that do the sparking light brown with a bit of coke / oil here and there. (They were bosch w6dc). I think that's the right colour now we don't have lead oxide.

 

Ignition seems unlikely because I've replaced all from the electronic pack that S&S fitted a year or two back and which should be good AFAIK. It's also fine when not under load, and tends to smoke after a sustained high speed run with moderate revs, also pointing to crankcase pressure.

 

So I think blowby is the problem.

 

Can I change the rings as a set and expect this to renew the compression, given it is fairly uniform across all cylinders?

 

On a similar front, if I have the pistons out, is it a good idea to change the big end / main bearings at the same time without bothering with the expense of machining? I would imagine the ones in there are pretty flat by now.

[marvmul]

There may well be blow by, but this doesn't explain the symptoms. Try to find the reason of the 'stuttering and trashing' when accelerating above 4300 rpm.

When an engine is stuttering, or severely missing beats, the oil consumption is much much higher (especially when there is bore/ring wear) than with a nice revving engine.

There may still be electrical problems, or fuel starvation when accelerating, or even wear on cam lobes (you can approximately measure the wear on the camshaft by measuring the valve lift).

[martynharrison]

When I had the engine looked at last srping, the garage repaired a big hole in the pepperpot to be found on one of the rocker covers. It's the oil trap in the breather sytem.

 

The original installation consisted of the pepperpot, reduced in size by welding to about to an inch and a half high instead of three, and with the pipe at the end bent over almost flat so that it would fit under the bonnet. A gross bodge job, IOW.

 

Probably from that point, the pipe was cracked and leaking oil and crankcase gas on the side hidden underneath it. The rubber hose originally went into a three way union made out of a piece of coke can and gaffer tape, and then via two hoses to the SU carb vaccuums.

 

With the Holley, it ran more or less ok, but was leaking oil out of the side of the head where the pepperpot is (was). Also, the single pipe was now fed into the pancake filter rather than carb vacuum suction.

 

When the garage was looking at the oil leak, they put a second piece of hose, with a smaller diameter, onto the end of the first hose and sealed up the crack in the top of the pepperpot.

 

From then on, it was horribly strangled when revved.

 

Since I'd put a different inlet manifold and composite head gaskets on by then, there were a number of reasons this might have been happening, e.g. I wondered if the increased thickness of the gasket was lifting the rocker shaft and so reducing the valve depression. No, as they're hydraulic lifters, etc.

 

A conclusive test of this was when I took the rocker covers off, checked the rockers were rocking up and down handily on the starter motor suggesting no cam trouble, and put back some other rocker covers where the pepperpot wasn't actually welded into the hole.

 

Putting the two new covers on, and the way these are done they have an oil filler at the front, and two pepperpots at the back where there is more room for them (custom hole cut for the filler at the other end), I left the pepperpots open to atmosphere and found the engine no longer had the same stuttering effect at the same revs, basically this solved it. Putting the old hose combination on one and plugging the other, back came the rev limiter at about 3800 / 4000 rpm.

 

At this point, I concluded there was too much blowby and the crankcase pressure was causing the engine to splutter and stop pulling.

 

Now it is a lot better than it was, with twin pepperpots and some plumbing fitting with hoses, about 3/4 inch bore like the pepperpots have and duplex so that oil should end up being pushed round rather than blocking, it ought to be breathing pretty well compared to most. But it feels like it isn't.

 

I was expecting this to be excessive blowby due to cracked piston rings and when I compression tested it, was expecting there to be two or three pots well down compared to the others, but they're all similar, 120 - 130 psi. However, they are apparently below what they should be so I guess the rings are worn uniformly and/or possibly the bores are worn.

 

Excess blowby would make even a pretty open breather system stuggle, was my thinking, so a year or two on and having been to France and the like, any wear and tear will have gotten worse.

 

Exhaust is an S&S twin bore with tubular manifolds, I'll assume this is ok as it was ok when first fitted and stainless should just start blowing rather than constricting (and not for years yet).

 

Fuel pump is ok, it clicks away merrily when turning on after a week, then settles down to the odd click. If pressure were to drop, the pump would click more often to compensate. All pretty new as well. It does not feel like fuel starvation to me as I've had before.