[JOHN'S TR6]

My TR6 is nearly approaching it's 6 month winter layup.
After reading a section in October's Practicle Classic mag, i noticed an interesting suppliment on how to decoke the Piston heads and inlet and exhaust valves.

Having shone a light through the spark plug holes, i can see all sorts of dark crud on the top of the pistons and my compression is not brilliant.

The main reason that i am willing to go ahead with this is a leaking head gasket on the near side; only leaking oil. I have read many times on this forum, of people leaking oil from the head gasket. It seems to be quite common. I have checked the torque on the head bolts.

For those of you who have changed the gaskets, have you managed to stop the leaks?

I am also wondering if the crud that is probably on the valves may actually be giving a bit of protection against the unleaded fuel as i am only using additive.
Is De-coking a futile excercise and a waste of time.

John

[foster461]

JOHN, on Oct 6 2008, 08:46 AM, said:

My TR6 is nearly approaching it's 6 month winter layup.
After reading a section in October's Practicle Classic mag, i noticed an interesting suppliment on how to decoke the Piston heads and inlet and exhaust valves.

Having shone a light through the spark plug holes, i can see all sorts of dark crud on the top of the pistons and my compression is not brilliant.

The main reason that i am willing to go ahead with this is a leaking head gasket on the near side; only leaking oil. I have read many times on this forum, of people leaking oil from the head gasket. It seems to be quite common. I have checked the torque on the head bolts.

For those of you who have changed the gaskets, have you managed to stop the leaks?

I am also wondering if the crud that is probably on the valves may actually be giving a bit of protection against the unleaded fuel as i am only using additive.
Is De-coking a futile excercise and a waste of time.

John

Hi John, interesting comment re the head to block joint leaking oil as I have the same problem if I rev my engine beyond 5000k so I'm curious to know more about that also.

I dont think that carbon build up on the valves is going to help with recession. That is a problem caused by the valve hitting the seat and picking up metal which over time erodes the seat so no carbon here to help you. There is plenty of anecdotal evidence to suggest that this is an old wives tale anyway.

In general, excessive carbon build up is detrimental as it reduces the combustion volume and it has a tendency to heat up causing pre-ignition and dieseling issues so at some point it is good to clean things up, ideally when there is other work to be done like replace the head gasket.

Stan

[Richard Crawley]

Carbon build up in & around the valves will have an effect on gas flow & can lead to localised overheating & pre-ignition (pinking). This was very common up until the early 70’s & was mainly cause by poor quality post war fuel & oil products coupled with pre-war combustion engine design & it was not uncommon for engines to require a de-coke every 10,000 miles or so. The Triumph 6 (although old) does not fall into this category &, if in good condition, should not coke up unduly. Excessive carbon build up is more likely to be caused by an overly rich mixture &/or burning oil; this can be due to bore wear/glaze, broken/stuck rings, knackered valve guides or, if you have an external rocker oil feed fitted, that could well be the culprit.

You say compression is not brilliant, is this across all cylinders or just 1 or 2? It could just be down to poorly seating valves in which case a clean up & lap in will transform the engine but it could also be due to a bore/piston ring problem; an “oil down the plug hole” compression test will usually give a clearer picture of which is the cause. Fix the head gasket leak & obviously sort the valves if the oil test shows a problem; cleaning the coke off them will have no effect on “lead memory” (if you still have any!), lapping in the valves will but if your using a quality substitute it should not be a problem. Personally, I would concentrate on identifying why the compressions are low & fix that; be careful how you proceed, if you have a problem with piston seal & you clean all the carbon from the piston crowns, things could suddenly get an awful lot worse! When de-coking high mileage or suspect engines, it used to be common to leave a 3mm ring of carbon all around the outside edge of the piston so as not to destroy the natural seal the carbon gives.

[JOHN'S TR6]

Richard and Stan
Thanks for the replies.

Richard, you may remember i posted last week on the compression and after doing the oil down the spark plug hole test was a little worried by a general raising of compression by about 10 psi. Other comments back suggested 10psi was nothing to worry about. Must admit, it was greater than expected.

You mentioned lapping in the valves. I have seen the tool for this in a magazine and the Haynes but can you explain to me exactly what lapping is trying to achieve. I need to understand the logic.

Not having removed the head on this car before i am a little curious as to the condition of the valves/guides and springs.
coupled with the badly sealing gasket on the near side of the engine near the engine number.

John

[Richard Crawley]

JOHN, on Oct 6 2008, 06:59 PM, said:

Richard and Stan
Thanks for the replies.

Richard, you may remember i posted last week on the compression and after doing the oil down the spark plug hole test was a little worried by a general raising of compression by about 10 psi. Other comments back suggested 10psi was nothing to worry about. Must admit, it was greater than expected.

You mentioned lapping in the valves. I have seen the tool for this in a magazine and the Haynes but can you explain to me exactly what lapping is trying to achieve. I need to understand the logic.

Not having removed the head on this car before i am a little curious as to the condition of the valves/guides and springs.
coupled with the badly sealing gasket on the near side of the engine near the engine number.

John

Apologies for not remembering but, as a daily contributor, I find it’s sometimes difficult to remember individuals & exactly who said what. Sometimes it’s better to continue the original thread if the progression is relevant as it gives folks like me with diminishing grey matter a chance to keep up!

I didn’t think your cylinder pressures were that bad; if they all consistent within 5% I don’t think you should worry at all; the actual reading may be down to the accuracy of your pressure gauge. Differential pressures slightly over that indicate something may need attention before too long but if it’s over 10% you have a problem which would benefit sorting sooner rather than later.

Lapping the valves ensures an air tight seal of the valves into the valve seats under pressure of the valve springs, which is essential. As for how to do it, this guy gives a pretty good description;

http://videos.street...ow-to_80862.htm

He's obviously an American & I’m not sure what “120 grit paste” equates to but if it’s anything like 120 grit paper, it’s pretty coarse! I have two ½ litre tins of Carborundum lapping paste identified as 360 coarse & 362 fine which I borrowed from the company stores when I was around 17; I start off with the course & then progress to the fine. I’ve used around 2/3 of the contents of each tin; that's an awfull lot of lapping but they will certainly outlast me especially as the only engine work I now do is for myself.

Must admit I’ve never had a problem with oil leaks & sealing the head so don’t really know what could be causing the problems many seem to be having lately. Only possible causes are incorrectly torqued head bolts, slightly warped head face or a crap repro head gasket.

---------------------00000000000000000--------------------------
Edit added: I obviously misheard our American friend, he said 280 grit not 120 but it’s still a coarser paste than I use.

This post has been edited by Richard Crawley: 06 October 2008 - 10:02 PM

[bob-menhennett]

John

The concept of lapping in the valves, exhaust and inlet is to form a perfect seal against the cylinder head.In production the valves holes are machined to set angles which the angles on the valves match.Over a period time/ mileage carbon builds up on the area comprimising the seal.The exhaust side suffers a little more than the inlet and if left too long will never seal properly and power drops off dramatically.
With everything working as it should..i.e. no where to escape to the fueling/ compression/ ignition/ power strokes of an internal combustion engine works efficiently as the manufacturer intended.

Bob

[JOHN'S TR6]

John, Richard,
Thanks for the explanations. Brilliant Video Richard.
Now I understand what it's all about.

John

[Richard Crawley]

JOHN, on Oct 6 2008, 10:16 PM, said:

Brilliant Video Richard.
Now I understand what it's all about.

A picture can be worth a thousand words, moving ones even more so; my thanks to our American friend.

[PeteK]

My dad was an engineer in the Navy. He showed me how to lap valves with a lapping tool. Most important is to make sure you do not stop the turning movement at the same point each time, for example by turning the valve only half a revolution each way: that leaves a wear ridge and spoils the seal. Make sure you spin the valve several revolutions for each hand movement- works like an old fashioned bodgers lathe.
But, to increase the speed of getting the job done, a Navy technique was to stand the cylinder head on iits side, oil the valve guide and stem, apply carborundum paste as normal to valve and seat, but then attach an electric drill to the end of the valve stem, and use that to rotate the valve.
Lets face it, most lathes now are electric powered, and I bet quite a few people have never seen a manually operated bodgers lathe.
I find a variable speed drill works fine for me, and my lapping tool is long gone.

[Richard Crawley]

PeteK, on Oct 11 2008, 08:23 PM, said:

apply carborundum paste as normal to valve and seat, but then attach an electric drill to the end of the valve stem, and use that to rotate the valve.
I find a variable speed drill works fine for me, and my lapping tool is long gone.

no No NO;
It’s frequently done but stuffing valves into a drill that’s rotating at relatively high speed & in one direction is the WORST, WORST possible way to lap in valves!

[BrianC]

Richard Crawley, on Oct 11 2008, 09:24 PM, said:

no No NO;
It’s frequently done but stuffing valves into a drill that’s rotating at relatively high speed & in one direction is the WORST, WORST possible way to lap in valves!

Oh so true! However, there is a drill attachment which oscillates and does a very good job. I bought one many years ago and used it several times. I still have it somewhere - not sure of the make, but I'm sure they must still be available at probably a few quid.

[Richard Crawley]

BrianC, on Oct 12 2008, 08:04 AM, said:

Oh so true! However, there is a drill attachment which oscillates and does a very good job. I bought one many years ago and used it several times. I still have it somewhere - not sure of the make, but I'm sure they must still be available at probably a few quid.

I never had one but I remember them well; called “Easylap” or something like that but I can't remember exactly. I’ve always used the old fashioned rubber sucker but with many bike engines, the size & position of the valves made it difficult to use so I had another lapper which consisted of a T handle with a small collet chuck on the end which you tightened over the end of the valve stem.