GT6 GT6 Engine Rebuild Questions...

[Flinkly]

hey guys,

as some of you know, i'm just starting a gt6 restoration. to begin the restoration, i'm rebuilding the engine since a car is useless without it. as far as previous knowledge about the car, i have none and can't really try to get any, since the previous owner has been dead for some time.

first, i haven't found anything not original on the car accept two guages that replaced what i assume to be bad guages, so my basic assumption is that most everything is stock. second, i know this car was driven in the early '80's down in california, so my second assumption is that it has been converted to use unleaded fuel. also, it hasn't been driven in about 20 years, not even started. so this is really the only information i have.

as far as the engine is concerned, it looks fantastic on the interior. some tappets have grooves in them around the top, but everything moves smoothly and looks great.

so here is the question, what should i replace or have done to the engine while i am rebuilding it? should i replace valves in case it hasn't been converted to unleaded? is there anything else i should replace as preventative maintenance?

i do plan on replacing all the tappets since some have grooves, and i will replace all bearings, oil seals and core plugs as preventative maintenance, and maybe even the oil pump if it is too far out of spec.

another question is where should i take it? will a regular engine machine shop be good enough for my british motor, or should i take it to someone who specializes in at least british motors, if not triumphs? oh, and just so you know, i'm taking it to a machine shop to have them check tolerances and grind where necassary, not paying for a rebuild.

thanks guys for all the help, this is my first engine rebuild and i want to learn how to do thigns right, and get a great engine out of it while i'm at it.

 

[dklawson]

I can only offer suggestions (based on other LBC engines I've worked on) as I haven't rebuilt our GT6 engine yet.

First, anticipate spending more than you expect. Call local machine shops until you find one you're comfortable with. If you're going to have them assemble the machined pieces you need to find one that's worked on LBC engines. If you're using them for machining only, find one with a good reputation regardless if they've worked on British engines before.

If you've already torn down the cylinder head, I'd clean it up and look for hardened inserts around the exhaust valves. If they're there... you'll find them. If they aren't there, have a shop install them. Check the valve guides for wear and anticipate that they may need replacing... which will eventually lead to a complete rebuild of the head as the valve seats will need recutting and the valves will require regrinding and lapping. Take a good look at the condition of the rocker shaft and inside bores of the rocker arms. These tend to wear quickly. Some fit external oil feed kits to supply the rockers. Hopefully someone will chime in about their merits.

I don't believe you should replace the tappets alone. In general, if the tappets are worn, the cam will be worn (and visa-versa). I replace them as a set, new cam with new lifters.

The machine shop will tell you what other things you should have done (regrind crank, straighten/re-size rods, shave the head, deck the block, etc). That's why I caution you to expect to pay more than you first anticipate. You won't know what's really required until it's all clean and measured.

Out of curiosity, which gauges were replaced and what was installed by the previous owner?

EDIT: I checked out your pictures and your signature line about $0 spent so far. I'll caution you about one thing. It's extremely easy to spend more on restoring a GT6 than it's worth (first hand experience!) Try not to count your receipts... it will only depress you. Also, I find with restoration work you need to force yourself to do at least one thing EVERY day. It's all too easy to put the project aside and uncompleted.

 

[Flinkly]

i'll have more pictures of the engine block and head torn down tonight, but the grooves on the tappets are from the head, not the cam. it makes me think something was in the oil that got stuck in there and caused some abrasion, the bottoms of all the tappets are perfect (aka, i think the cam will turn out to be perfect when i get the timing cover off). then again, i don't want to get it all together only to have an engine problem within a couple thousand miles.

about the guages, the more i think about it, the more i think he might have added, rather than replaced. the original two were still hooked up and resting in the radio "slot". i can't remember what they were for, since i don't plan on putting them back in, but i think one is for oil pressure.

 

[Alan_Myers]

Hi,

If you have never rebuilt an engine before, you might get some general books about it, just to familiarize yourself with the overall process. There are a number of things typically done that are common to most or all engines, and then there are the specifics and fine points to a particular engine like the GT6's.

In the same context, a good general automotive machine shop should be able to handle most anything that comes up rebuilding a typical Triumph motor to stock or slightly improved form. The key advantage to a specialist who works on LBCs and knows Triumphs would be that they might be able to recommend some shortcuts to speed the process or specific tricks to improve the engine and it's durability.

One important "trick" with the earlier TR 4-cylinder has to do with converting to the phospor bronze "unleaded fuel" valve guides. The new materials expand a bit more than the original type when the engine warms up. So, on these particular engines, a machine shop that's strictly following sevice manual specifications might hone the valve guide made from the new materials too tight, and that can too easily cause valves to sieze.

Now, I don't know for certain if this is also a problem on the GT6 or other Triumph 6-cyl. motors. But, I think it's worth checking out. The solution with the TR2/3/4/4A replacement guides, is to hone them slightly oversize: say .001-.0015" on intake, .002-.0025" on exhaust (because the exhaust side are hotter in normal running conditions).

Again, I'm not sure this is true for GT6, but it seems to me it would be and is certainly worth lookign into. A siezed valve in a freshly rebuilt engine ain't no fun at all and this is an easily avoided "error" that can be caused simply by following service manual specifications.

Unless mileage on the car is extremely low, I suspect you will at least need to get a reground camshaft and a new set of cam followers (tappets). For the cost, I just don't think it would be wise to ever re-use a cam in any engine with more than, say, 25-30K miles on it.

Throughout the engine, all the bearing surfaces need to be inspected and measured for wear. These include the cam bearings, mains, and both ends of the conrods. Most would not re-use the existing bearings, unless mileage is extremely low and there is virtually no measurable wear. The cost of bearings is low.

Whenever they are reworked/reground, the camshaft and crankshaft can benefit a lot from hardening. The most common process is nitriding. This creates a hard surface on their bearing journals and the cam's lobes, that helps these key parts live a long, healthy life. There are at least two types of nitriding, with one of which the parts are pretty much ready to use right after, the other they should get some micro-polishing before installation. Many machine shops have access to this sort of hardening process and can best advise you.

I agree about the likelihood that the rocker assembly will need a rebuild. These are simply more prone to wear than the rest of the engine. If you rebuild it, try to get an upgraded, harder version of the rocker shaft itself. An option here is to use roller rockers, which will run a little quieter and tend to help the valve guides hold up longer. It isn't cheap, but many people like to do this modification. Although many consider these a high performance item, rollers don't add or save significant horsepower. If you choose to use roller rockers, I strongly recommend staying with a close-to-stock 1.5:1 ratio and not getting caught up with "improved" rocker ratios (1.6:1, 1.7:1, etc.). These can lead to other problems and many things need to be carefully considered before modifying an engine with them. Plus, they change cam/valve timing in a way that the cam designer wasn't expecting, and might give unexpected results.

While it would be nice to improve rocker assembly lubrication a little, I'm not a big fan of the external oil feeds to the rockers. These tend to increase oil being burned (i.e., getting into the cylinders through the valve guides) and rob oil from the main gallery, which I consider far more important. The rocker assembly is far easily accessed and inexpensive to repair than the mains, so I'd rather have the bulk of lubrication going to the heart of the engine: the crankshaft.

In fact, I think I've read that GT6 in particular tend to have low oil pressure on the front main, too. Stealing oil for the rockers can only make that problem worse. Better yet, external oil feed piping and hoses can be used to distribute oil pressure better to the main bearings, front to rear.

Speaking of oil pressure, think twice about that gauge. I hope to get a Mk III to restore some day myself. Looking at info about the cars, I figured adding an oil pressure gauge would be high on my list. I wouldn't want to be without one on a high revving engine! Unless your goal is strict originality, this one gauge provides some of the most important info about the engine. To me, the other key one is coolant temp. Also, it sounds like the extra gauge installation was done in a manner that's easily reversible, should that ever be important for originality's sake. Another way is to hang it below the dash in an accessory panel. It's up to you, of course, but I personally like to know how the oil pressure is doing in my cars' engines, especially if there is a catastrophic failure (I suppose the "idiot light" would alert about this, though).

If that car hasn't been driven since the early 80s, I would suspect it's *not* been converted for unleaded fuel. In those days both types of fuel -leaded and unleaded - were available. Some quick ways to check the cylinder head's status include: look for hardened valve seat inserts, especially on the exhaust side; check for bronze colored valve guides; and see if the valves are stainless steel (a magnet won't stick to them).

I'm not certain the same is true of the GT6 cylinder head, but do I know the TR4A and earlier 4 cyl. heads are actually more comfortable using unleaded fuel than might be suspected, just based on the cars' age. The metal alloy used in the heads is a bit better resisting valve recession than was expected. Probably the original valve guides are a bigger concern in those earlier heads, will wear faster. So, I'd not take apart an otherwise good running TR 4-cyl. motor *just* to convert it for unleaded fuel. However, if it's apart and being built for any other reason, I'd definitely do the conversion then and have it out of the way.

Even if you keep the engine rather stock, there are many subtle improvements you can make that will help the car run well. One is a slightly hotter cam. Original Triumph cams were pretty mild. Another is to have the flywheel lightened a bit. Simple port matching on the head and manifolds is a good idea, too.

Anything that can be done to improve engine cooling is a good idea. It's not that I'm aware of the GT6 having any special problem in this area, just that all British cars seem to be built for cooler climes and anything that can be done to help keep them operating at comfortable temps is a good thing. This starts by cleaning the block and includes checking that coolant passages from the block to the head are well-matched and not obstructed by the head gasket. There might be some other, GT6-specific things that can be done.

Although I think you are mostly considering the basics and wanting to rebuild the engine to good, original specification, looking at the GT6, it appears to me it is seriously under-carburetted. This is one area I'd consider upgrading, if you are interested in that sort of thing. I'd prefer to see at least a triple carb setup. Or I might consider EFI, but that would be pricey. I've also seen PRI's installation of six individual "motorcycle" carbs on a GT6 and that seems like a great improvement (and looks very cool!). The other area that nearly all Triumph engines can use improved is the ignition. Old points-style ignitions have almost entirely given way to today's electronically controlled, high energy systems for a bunch of good reasons: increased performance, better fuel economy, improved starting, high reliability and low maintenance.

But, these are certainly things you might or might not want to do.

I'll be interested to see what some folks who know the GT6 engine more than me might add to this thread! Any tips will be really useful when a Mark III finds it's way into my garage! /ubbthreads/images/graemlins/wink.gif

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[dklawson]

Alan, I've got a couple of follow-up questions for you regarding your post. With BMC A-series engines there is always a debate about whether bronze or iron valve guides are better. Whether I've discussed this with people with street or race engines... I have yet to find a consensus or evidence to support one material being better than another. I'm not contradicting your suggestion, I'm just curious why you feel the bronze is better and would appreciate your comments.

My second question is about stainless valves. I've never worked on an engine with them and haven't googled to find out what material is used. I would have thought a 400 series stainless would have been used for its relative hardness compared to the 300 series materials. While 300 series steel is non-magnetic, 400 series stainless is somewhat magnetic. What material is used in stainless valves?

 

[Alan_Myers]

Hi Doug,

Phosphor bronze valve guides are simply the "usual" replacement for the original types of guides used to convert a Triumph cyl. head for unleaded fuel. I'm not necessarily saying it's "better" than cast iron, just that the phosphor bronze material is most usually what you will get if you ask for "unleaded" guides for any Triumph cyl. head. Phophsor bronze apparently has some self-lubricating properties to help it survive in the tougher environment of unleaded fuels. There might be other special types of "unleaded" guides, even specially-prepared cast iron ones. I don't really know for certain.

The original guides relied upon lead in the gasoline to lubricate them. So, without lead in today's fuels, the original-material guides might wear more quickly and, very worst case scenario, might sieze due to lack of lubrication if in a close-tolerance situation.

Of course, in both cases in Triumph engines, a little oil inevitably gets into the guides and helps provide a bit of lubrication too, just not enough to rely upon all the time. (Note: I'd never install seals on the guides of these old engines! IMHO, the engines need a little oil coming in through the guides, most of which will end up being burned in the combustion chamber of course.)

My main point though was that the phosphor bronze guides have a different rate of heat expansion, compared to the originals, and have been known to sieze valves when installed strictly following the service manual specs for honing (i.e., specs for the original type of guide). We saw an example of that here on BCF just recently, in a freshly rebuilt and "unleaded" TR3 motor with only a few miles on it. So, slightly oversize honing is recommended for those particular guides. I know this to be true of the 4-cylinder TR motor, and personally would want to do some extra research to see if the same is true of the smaller 4-cyl. and various 6-cyl. Triumph motors of the same or slightly later era. (Note: By the time of the TR7/TR8, I would feel pretty certain the engines were being built to handle unleaded fuel.)

I'm no metallurgist, so can't really answer your questions about stainless steel alloys with any sort of expertise. I was using the term pretty generically. You are correct that some stainless steel is mildly magnetic. The most common type I've seen offered for use in TR motors is "Stellite", which I think is a brand name of sorts. I've got a set around here somewhere and will check them for magnetism the next time I run across them. I do believe many modern "unleaded" valves are high nickel content stainless steel, which makes it one of the "higher" grades of s/s, probably with other alloys added to also increase hardness. Again, the idea of changing from the original valve materials to s/s valves is simply to hold up better under higher temps with minimal lubrication, which are the result of switching to unleaded fuel.

Hope this helps clarify. I'm sure you could google up some more detailed and specific info regarding stainless steels, if you wish.

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