GT6 Mk1 GT6 Engine Rebuild

[dklawson]

For 20+ years I have delayed rebuilding the engine in our '67 GT6. It cannot be put off any longer. Since the car is original and has been in the family since new I have decided to rebuild the original engine rather than "upgrade" to a Mk1/3 engine.

At this time all I have are the factory and Haynes manuals. I would appreciate references to any other texts and/or web sites that discuss the early engines. Also, if you can share any recommendations for tweaks that should be done to improve the reliability of the engine and improve its lube and cooling systems, that information would be greatly appreciated.

Richter (if you are out there) I have your web site bookmarked but I would value any comments you care to add.

Thanks,

 

[TR6BobNF]

Doug:
Many options open to you and I'm sure others who actually own GT6's will comment here. My sole experience with a GT6 is an old round tail that I dragged out of a field and scrapped for parts. It was so far gone I did not get much off it but it was fun picking it apart.
Two suggestions for your cylinder head though; first is to have the head decked or trued by a good shop to ensure it is perfectly flat. Shaving for increased compression is entirely another story. Second, consider having hardened exhaust valve seat inserts machined into the head allowing you to run unleaded without damage to the head. That's a very standard upgrade on rebuilds. Good luck and post pics.

 

[Eddie6775]

I rebuilt my cylinder head a year or so into owning my '67. I didn't do much out of an ordinary valve job, good cleaning and some careful flat lapping to the mating surfaces. I did however do a tiny bit of reaming of the exhaust manifold bolt holes, because when I got the car the manifold was cracked at the number six exhaust port so it was more of a preventative measure to protect the welding job (cast is a goober to weld btw..).This mod was just to let the head expand and contract with out to much side ways pressure build up on the exhaust manifold studs. As I recall I also took my Dremel to the intake and exhaust ports and just smoothed up a little. Nothing high performance, but I think it helped prevent fuel pooling in the intake during cold start up and in theory improved the efficiency of the engine. I went back after a week of running and checked the tappet adjustment too. I later found that a.001 tighter tappet adjustment on the intake side than my book called for made a big difference in engine noise and was slightly more responsive to the throttle. I never did find an easy way to get the push rod tubes not to leak though!

The '67 is a beautiful car. Glad there's still some on the road!

 

[vagt6]

Eddie, welcome to this great website. It's great to see another GT6 enthusiast here. Please keep us informed of all your resto efforts and photos.

Doug, I, for one, am exited to "watch" your restoration on this website. There aren't may MKI GT6s left to restore and with your excellent skill level, I'm sure this will be a great restoration to observe.

FYI, please check out his website here, which nicely chronicles a total restoration on a MKI GT6: https://www.gt6.ca/

If I'm not mistaken, Andre retained the original MKI engine, modified it, and occasionally races it. At any rate, it's great documentation and a fun saga of a MKI GT6 restoration.

Good luck with your efforts with this rare and beautiful car. Please post photos!

And, cheers to you for rescuing another Triumph GT6. :thumbsup:

 

[glemon]

Not to hijack the thread, but what is the .001 valve adjustment on the intake side discussed, I assume tighter, or closer, but you know what happens when you assume....

 

[dklawson]

Hi Mark. I have exchanged a couple of emails with Andre about his rebuild and some of the other tweaks he has done to his car. I am considering some of the things he did for the cooling system. He does have a beautiful car.

I will only be doing an engine rebuild. Though my wife would like to have the car repainted... I'm not even 100% done with painting the Spitfire. I don't want to take on another painting project anytime soon.

 

[Eddie6775]

Hello, Tightening the valves ever so slightly increases overlap at the end of the exhaust stroke leading to the intake stroke slightly and so it's supposed to help with chamber scavenging. On my gt6 I actually do both intake and exhaust but you have to be careful with the exhaust. too tight and that valve can burn more easily. I have an old celica with and aluminum head and go .002 under on both but I'm not so adventurous with the GT6.

Hope this clears it up. It seems to work for me :hammer:

 

[dklawson]

Today I started the tear down of the removed engine. What I found prompted me to call my father-in-law and ask him to take a trip in the way-back-machine.

My father-in-law raced our GT6 in the late '60s and early '70s. Some of what I found in the engine today did not match my expectations for a stock engine so I wanted some clarification.

It turns out that while this is still a Mk1 engine, it is not this car's original engine. The engine was "swapped" for a race prepped engine from a builder in SC. I found the block has a sloppy +.040" overbore and VERY loose pistons. When you look at the pistons in their bores there is a VERY wide gap... something more than .015". I suspect this was done to keep things "loose". The valve gear also was a surprise as it had some massive dual valve springs. I think the valve springs contributed to the awful condition I found the lifters in. Six of them had concave contact surfaces with deep pitting.

If this engine needs to be bored out it would have to go to +.060". So far BPNW is the only vendor I have found who says (at least on their web site) that they have flat top pistons that big for the 6-cylinder.

Over the next few days I will be reviewing all my options and will make a decision on how to proceed. I was hoping this was going to be a quick and easy rebuild but it looks like that is not going to be the case.

 

[dklawson]

Update 12/19/11

The head passed crack and pressure testing so I will use that after cleaning up the ports, having hardened exhaust seats added, and all the valve seats re-cut. Of course it will also be checked for flatness. Before returning to the shop I will also cc the chambers and make sure they are all close.

The headers (Mk1 are different than later cars) required a bit of welding to patch pin holes and grinding to flatten the flanges. That is done and soon they will be coated with POR's high-temp manifold paint.

I ordered the +.060 pistons after the machinist looked at the block and thought there would not be a problem at that overbore. Obviously I'll have the block hot tanked and install new freeze and galley plugs. The machinist will also check that the main bearing bores are concentric and inline. I have also asked him to check the block and deck it if necessary.

I found that the crank has welded up journals. The machinist is checking it for size and general condition. Hopefully I can use it even if it has to be reground.

The con-rods look great. I am having them checked for straightness and big-end size.

I ordered the S2 grind cam from TSI. I will also be ordering a set of new springs, followers, cam bearings, and assorted other parts from TSI.

Meanwhile I am cleaning and painting individual parts removed from the engine and engine bay. I've got to do something while waiting.

This is still going to progress slowly but at least there is progress.

 

[vagt6]

Sounds like you're headed down the right path on your enging, Doug. Please keep us posted!

 

[70herald]

With the 6 pot engines, I believe that slightly drilling out the oil passages on the block to reduce starvation of the middle bearings is recommended.

 

[dklawson]

Update 12/20/11

What a difference 24 Hours can make... for the worse.

I arrived at the shop with my +.060" pistons and rings and the machinist asked what size they were. I thought this odd since I told him earlier that I would order +.060. After looking at the block he has cold feet. It turns out the block has already been sleeved and there won't be much material left after going to +.060".

Then there is the crank. He likes the way it looks but it measures about .002" undersized. However, with the con-rods on the crank, their bearing clearance measures in spec. I will be taking the old main bearing shells to him today so he can do a similar running clearance check on the crank in the block.

Heavens knows where this is going. I may yet be using the old 2000 sedan block modified to fit the GT6. At first glance it appears to be still on the stock bore.

 

[vagt6]

Doug, is the 2000 sedan block a MK II 2000 engine?

Too bad about the MK I engine. If you want to use a MK I engine, let us know. I'd like to believe that you could find one fairly cheap.

Let us know . . .

 

[hondo402000]

can you put a TR6 engine in the GT6, they can bore it 060 over with no problem I bored mine to 78mm, I have seen several TR6 engines for sale cheap

Hondo

 

[dklawson]

This is my wife's car and she wants to retain the character of the Mk1 complete with its early engine.

The machinist wants to try manually honing the bore out the additional 0.013/0.015" necessary but I'm worried that too little wall will be left on the sleeves.

The 2000 sedan block I have is from a '67 Estate. It is the same as a Mk1 GT6 block... but different. For whatever reason the bosses on the block for the engine mounts are VERY different. I think that is strange in itself since the 2000 is supposed to mount off the front plate, not side bosses. I can easily address the different mounts on the right-hand side of the block but I will have to be more creative and do more fabricating on the left.

The problem with finding/using another true Mk1 GT6 block is finding one within a reasonable distance at a reasonable price. Most the engines and blocks I have located are far away making shipping necessary. My plan at this point is to start making the adapter plate for the right hand side of the 2000 block after which I will have a good support (and reference) surface allow machining the left side of the block. Once I bite the bullet and get that done I will at least have a second block to discuss with the machinist.

 

[dklawson]

12/29/11 Update.

Ted Schumaker from TSI is selling me a short block for the engine rebuild. He is planning a trip to central NC for January and will bring it with him on a trailer. The short block should give me both a new/correct Mk1 GT6 block and potentially an unmodified crank.

In the meantime I have been carefully examining the headers and fixing pin holes and hairline cracks in them. I have also cleaned up the flanges so they will be the same thickness as the adjoining flange thickness as the intake manifold.

The head already has a decent job of port matching done but I will be cleaning up the ports a bit and fitting new machined guides before taking the head back to the shop to have hardened exhaust seats fitted and to have all the valve seats re-cut and the valves reground.

This is taking infinitely longer than I anticipated but it will get done eventually.

 

[dklawson]

1/7/12 Update

Ted S. from TSI sold me a core Mk1 GT6 engine which I picked up last night. This weekend I will disassemble and clean the parts for delivery to the machinist.

I called the machinist to tell him I had purchased a short block and he said "That's probably a good thing. I looked at that block again (my old block) and I think the liners would fall apart if we tried to bore to +.060in "

Ted also provided me with a reground S2 cam (using a core I provided), new lifters, and new valve springs. I have opened up the ports in the head a bit and will work on that some more before fitting new, modified valve guides. Once the guides are in I will take the head to the shop to have hardened exhaust seats fitted and the valves fitted.

I have welded up pin holes in the exhaust header, flattened the header flanges, and worked on matching the header flange thickness to the intake manifold flange thickness. The Mk1 manifolds attach differently than on the later engines and it is somewhat important to get the flange thickness matched if the manifold gasket is to seal properly.

EDIT: I started disassembling the short block this afternoon. It looks like I am back to "waiting". This block has been frozen and a rather nasty poor welding job was done to re-attach a large portion of the water jacket wall on the right side of the block. Ted says he will send me another bare block soon. This engine really does not want to be rebuilt!

 

[dklawson]

1/19/12 Update.

TSI was unable to supply me a replacement Mk1 block for the one that had the freeze damage. I was looking at around $240 more for the block that was available... on top of the money already spent.

I looked at my options and spent the weekend of 1/14-1/15 machining adapter plates that will allow me to use the TR-2000 sedan block in my GT6. The early TR-2000 blocks mounted off their front plate instead of bosses cast into the side of the block. However, the 2000 block does have stiffening ribs and bosses for some form of envisioned engine mounts that were not used. I attached my adapter plates to those features.

I finished that task along with my minimal amount of head porting and took the parts back to the machine shop yesterday. They now have the block from one engine, the head from another, and the crank from a third. Between all those items I hope to put together a sound and reliable engine. For the moment I am back to cleaning and detailing ancillary parts and waiting for the call from the machine shop to tell me what size bearings and pistons I need.

Obviously more to come.

 

[vagt6]

I've been waiting to hear about your update, Doug. Your engine sounds like it's gonna be a great one. Involving Ted Schumacher is a no-brainer, there are few experts on this continent who are more knowledgeable about the Triumph GT6.

All the careful preparations you've taken will pay off handsomely. Such a "piecemeal" engine seems only natural for your MKI. So what if it doesn't have an original MKI engine? You said that the car is going to be a driver, not a trailer queen, so your Saloon 2000 engine is perfect for the application.

Please keep us posted with photos, etc. There aren't many of these GT6s left to restore, especially MKIs, and as you've seen some parts are increasingly difficult to source.

Most importantly, good restoration narratives such as your here may prove critically important to future restorers. In a relatively short time all the GT6s worth restoring will be gone. Suffer the thought, but it's true.

Thanks for posting this stuff, Doug. It's valuable information, and thanks to Basil for creating this repository of information about these great cars.

 

[dklawson]

Pictures will come soon. At this point there has not been any progress worth recording. Two months in and the machine shop has only helped me by crack and pressure testing the head!

The head is also the only place where I have been able to make progress. I enlarged the ports a bit and machined new guides to the profile suggested by Vizard in his book on modifying TR engines larger than 1300cc. (PDF copies are available online). The ports do look more open and less restricted.

I have also worked a lot on the old header. The flanges are now flat across all the mounting area, all pin holes have been welded shut, and the flange edges have been modified in thickness to match the thickness of the intake manifold flanges. In the end it should bolt up and seal better. I considered buying "new" until I found out how expensive the Mk1 headers have become.