Gloopy Tar on Pistons - Experts Thoughts

[oldtuckunder]

Ok hopefully last conundrum on this strip and rebuild, as hopefully crank and rods on the way to being sorted.

 

When I pulled the head off I went Yuk at the sight of the top of the pistons they all had a gloopy oilly tar on the top after two years I expected a bit of burnt oil or a bit of carbon but this stuff is weird. I have attached three pics, 1 as it came out, 2 just wipped with a rag and sort of looking what expected and 3 just wipped with a bit of thinners on a rag looking tarty and smart again.

 

 

Sorry can't upload the final clean one as the web-site uploader seems to have gone on the fritz

 

So how did this gloop get there (on all of them) and why hadn't it burnt on?

 

I'll give you a bit more info to try and cut down the guessing. Ignore the very wet look in first picture that is clean oil from running a dry then wet compression test just before I pulled the engine.

 

The compression figures taken when the engine was warmed up were (allowing for accuracy of the guage which was a good screw in one):

 

1-6

152, 150, 150, 151, 150, 160 DRY

155, 155, 150, 150, 150, 160 Second DRY

160, 158, 160, 160, 155, 170 WET

 

Fairly consistent all well within 10% not sure why 6 is always 10 higher than the rest.

 

So not **** compression figures, but unfortunately I don't have a set from after rebuild last time to compare, I will this time.

 

So compression figures don't at face value look too bad. I have popped the top ring of each piston and remeasured gap in the bores and they all came out at .020/.021 which was what they were gapped to when fitted so I don't think I have worn bores. Will get them checked for oval wear when its in the machine shop next week.

 

So I'm wondering if it could just be the oil control rings that have been allowing oil up the bores to form the gloop?

 

How do I check fit of oil control ring set?

 

OK further factoid that may help diagnosis. Oil Changed begining of 2014 season came out looking real clean. Oil changed Mid season oil came out clean, then engine developed knock and play for the year ended. Just drained the oil and it looks blacker than I would have expected for only having done a couple of competitions and possibly 100 road miles testing.

 

So am I getting oil up the bores (forming the gloop) and gasses down the bores spoiling the oil? NB the inside of the rocker cover was as clean as clean can be. The head chambers are a bit sooty but not much more than I expected.

 

OK one further detail in case it helps diagnosis. Since rebuild there has always been a very fine misty oil haze coming out the rocker cover. I run straight to a catch tank and whilst the haze was always clean (runs through a clear pipe) I suspect each event would put about a fluid ounce in the catch tank. and during the season between oil changes I would probably have to top up with about a litre of oil in total. So the engine from rebuild did consider oil as a consumable, but never enough to worry about and given that the bores were intentionally set .004 oversize probably what I would expect.

 

OK guys any thoughts?

 

 

Alan

 

 

 

[Nick Jones]

Oil burning - probably quite alot. The 2L burns quite well and has to be really sick to give blue smoke. I wonder if the rings never bedded properly and the bores glazed?

 

You're probably also getting lots of blow-by, so there'll be water and combustion deposits in the oil. Had very similar deposits on my old PI engine (though they were on top of the more conventional baked deposits). It also had loads of blow-by (worse than you describe) and turned the oil black very quickly. This was due to being well used then left standing for 15 years so the bores went rusty. It was then simply "cracked off" and run.

 

I suspect another factor in yours is that it rarely gets a proper long road run so rarely sees a full, completely heat soaked condition to cook the deposits.

 

Nick

[Motorsport Mickey]

I think Nick is not far off the mark. With the piston/bore clearance set at .004 thou there's plenty off breathing space (hence the oil mist) and if the engines only done 100 road miles not enough running at BMEP* critical revs to fully bed in the pistons (unless you did it on a rolling road), and my guess is glazed bores. The running at competition speed doesn't count, you'll have been using revs and lower gears not what the engine demands at all.

* Brake Mean Effective Pressure.

 

The radial pressure on the rings should still be ok but as confirmation check the measurements between the bore and pistons, remember the pistons are ovaloid check in all planes. My guess is rehone the bores and refit with new rings (old ones will be glazed) and straight from the get go give it BMEP running, (the camshaft will be as good as gets now). Top gear up motorway gradients and give it full throttle (down to the floor) from bottom to top of it's torque range and then come off the throttle, brake the car down to bottom of torque range and do it again, and again. When you run out of gradient come off the motorway and go back the other side and gradient it the other way, I've been known to spend a pleasant 1 1/2 hours doing this as the piston rings expand and gouge (we are talking microns here) grooves into the cylinder walls and improve the compression and also the oil scraping off the walls .

 

Mick Richards

[oldtuckunder]

Wow guys! lots to work on, isn't experience a wonderfull thing. After getting the bores checked if they were still within tolerance I was going to get them cross hatch honed and had been thinkingg about a new set of oil control rings, but now I can see why a new set of rings and bedding them in properly might be so important, hadn't thought that competition use was the wrong use to get the rings bedded in.

 

So question is will I be able to find a new set of rings for the pistons? if memory serves me right (not a given at my age) I think they were a set of AE's that I had boxed for about 30 years! If i'm right (and please correct me if i'm wrong) but dont/didn't piston manufacturers each have their own ring groove & dimension tollerances, i.e. rings designed for one piston won't always fit another (or am I just blowing smoke like my engine?)

 

i.e. is getting a new set of rings for existing pistons easy?

 

Regards

Alan

[john.r.davies]

Mick,

No argument, but in your full explanation above, saying, "...come off the throttle, brake the car down to bottom of torque range and do it again, and again" did you mean "...engine brake the car .."?

I'd suggest that will then maximise the 'vacuum' in the chambers and draw oil up onto the rings, to lubricate them for the next full throttle phase and help avoid glazing.

 

JOhn

[Motorsport Mickey]

Good point and one I'd never thought of.

 

The advantage in using the brakes is it's more controllable when you carry out this on a public motorway, you can see people approaching from behind in your mirrors and carry out the brake and then accelerate process without getting in their way, sometimes on the long motorway gradients you can do this 3 or 4 times before you crest the hill. If you use the gears only your car loses acceleration quickly (but not as quickly as using brakes) without any warning brake lights to show following drivers something is happening in front. Needless when carrying this operation out you need to drive carefully picking your gaps and making sure you don't startle following drivers into unusual manoeuvres.

 

Even when the pistons are bedded in it's important to keep glazing away by working the engine in it's rev band when under load, most drivers do it without realising in their normal driving style but if you are a smooth cruiser used to "Driving Miss Daisy" then it's as well to invest a little time in keeping the glaze away, I'd rather drive it than strip it.

 

Mick Richards

Edited March 8, 2015 by Motorsport Mickey

[peter clarke]

Hi, I had a similar problem with a 4 cyl rebuild and turned out reconditioner had provided excessive clearance in valve guides allowing oil to be sucked into chambers. Oil was coming from top down not bottom up giving good compression reading.

[oldtuckunder]

Hi, I had a similar problem with a 4 cyl rebuild and turned out reconditioner had provided excessive clearance in valve guides allowing oil to be sucked into chambers. Oil was coming from top down not bottom up giving good compression reading.

Thanks something else to check, I'm running Stainless Valves in Steel Guides so its possible that wear has occured. Out of interest were you running with an external oil feed to the head?

 

I take the cure was new inserts?

[Guest ntc]

Thanks something else to check, I'm running Stainless Valves in Steel Guides so its possible that wear has occured. Out of interest were you running with an external oil feed to the head?

 

I take the cure was new inserts?

Running that setup you need to fit colleted seals.

[oldtuckunder]

Running that setup you need to fit colleted seals.

Dou you mean with Stainless & Steel or were to referring to the use of an external oil feed?

[Guest ntc]

Stainless need bronze guides,check the guides trim down to suit and fit these http://www.ebay.co.uk/itm/Genuine-Ford-Victor-Reinz-Valve-Stem-Oil-Seals-x-8-Escort-RS-Turbo-/151434836683?pt=LH_DefaultDomain_3&hash=item2342383acb

Edited March 9, 2015 by ntc

[oldtuckunder]

Stainless need bronze guides,check the guides trim down to suit and fit these http://www.ebay.co.uk/itm/Genuine-Ford-Victor-Reinz-Valve-Stem-Oil-Seals-x-8-Escort-RS-Turbo-/151434836683?pt=LH_DefaultDomain_3&hash=item2342383acb

 

I will check the guides and replace if necessary, a couple of reasonably respected "niche" Triumph suppliers who do compete had said that Steel Guides were fine with Stainless Valves but that they might wear a bit quicker. I'll check and see.

 

On the Reinz Stem Oil Seals, give me a clue, do they fit over the top of the Guide, I assume your comment "trim down to suit" meant machine the top of the guide to slip these over? and that they are held down by the springs so a double check for spring binding when fitted.

 

Alan

[Guest ntc]

They fit over the valve stem,the guide may be to high so cut to suit and yes the spring keeps it in situ.Binding will not be an issue.Are you using double springs?only fit on inlets

Edited March 9, 2015 by ntc

[oldtuckunder]

They fit over the valve stem,the guide may be to high so cut to suit and yes the spring keeps it in situ.Binding will not be an issue.Are you using double springs?only fit on inlets

Thanks! Yes doubles TR5 Red's (and no nasty Alloy caps!), Why only inlets (because there the ones that get suction on them on the inlet stroke, and the exhausts only get blow up them on the exhaust stroke)

[Guest ntc]

Thanks! Yes doubles TR5 Red's (and no nasty Alloy caps!), Why only inlets (because there the ones that get suction on them on the inlet stroke, and the exhausts only get blow up them on the exhaust stroke)

Correct.

[peter clarke]

On my 4 engine there was no aux oil feed and 4's do not have valve stem seals. It was just the excessive clearance in the guides that caused the problem. New guides and no oil burn / dry piston crowns.

[oldtuckunder]

A ten month later update on this issue as I have just pulled the engine again to find out what went rumbly in the bottom end at Shelsley last year. Head is off so I thought a quick update to this thread may help someone in the future.

 

Ok as a recap, gloopy tar on piston tops, would wipe off with parafin.

 

Had new bronze guides made, fitted and machined for each valve stem. I also had the tops machined to fit the Reinz oil stem seals, but didn't fit them as I discovered at the last moment that you cant use them with dual springs, and as I was really out of time I didn't have time to find either an alternative seal to go with the dual springs, or a single spring with the characteristics of the duals.

 

Also had the bores honed and fitted new rings, just in case it was a glazing problem after the rebuild the year before.

 

Following recomendations here I did my best to make sure running in procedure gave it as good a chance as possible of not glazing the bores.

 

OK so the engine did about 250 miles running in, and then maybe another 250 testing and competition use before the rumble started again (but thats a issue for another thread!).

 

Pulled the head last night, and hopefully the picture which I may or may not be able to attach shows that we still have some gloopy tar.

 

Hang on lets try and attach the picture as it will make description much easier.

 

 

Wow looks like it worked!

 

Piston 4 is as revealed, 3 is after just wiping with a rag no solvent. I did wipe another with parafin and like last year it came up clean as a new pin, so this oil isn't really burning on.

 

Couple of interesting points.

 

The cleaner areas are where the squish area is on the Mk1 head and where the inlet valve is situated, the tarry area is chamber/plug/exhaust valve area. On 3&4 the inlet valves are adjacent.

 

Note the number 4 showing on the piston crown, no I havent just marked that, whilst stripping cleaning everything last year I marked each piston with a normal black permanent marker pen, and the tar hasn't stuck to it! Wondering if I have just discovered a cheap non stick coating for piston tops?

 

Anyway I think I'm starting to come to a couple of conclusions.

 

1) Find and fit some oil stem seals to the inlet valves.

 

2) Use the car more! I have a feeling that after the running in & testing, whilst the engine gets up to temperature (I make sure it does) all it does is a few miles around a sprint track or up a hill and then gets put away for a couple of weeks before doing the same thing again. I'm wondering if this engine nevers gets hot enough for long enough to burn the tar off?

 

Anyway out to the workshop this evening to flip the engine and start looking at the bottom end for the serious problem

 

Alan