1973 GT6 Restoration

[DJB350Z]

Can anyone help identify these SU carburettors?

They don't have an ID tag with an overall code, and the various stamps seem to just point to the individual parts.

The manifold is a GT6 item and the carbs have been somewhat made to fit.

Not the best photos but hey..

[JohnD]

I'd think they are HD Carbs, but they look as if they have the flexible tube from the base of the float chamber to the jet, which makes them HS  type.

Throat size?

HD/S4 - 1 1/2"

HD/S6 - 1 3/4"

HD/S8 - 2" 

The 2", if it is one, is too big, flow velocity too low range with a 2L engine.

John

[NonMember]

I think the square flange on the manifold side makes them HS6 at least - HS4 were two bolt slanted flanges. I'm not familiar with the HD series to know what differences there are. The super-stubby dashpot neck was used on a few special variants (e.g. as fitted to Dolomite Sprint, I think).

[Steve P]

9 minutes ago, NonMember said:

e.g. as fitted to Dolomite Sprint, I think)

That's what they look like to me,HS6 on a short tract manifold with Sprint dash pots.

I have the same on my 2.5 Vitesse except that I have the long tract manifold which apparently flows better.Mine is flowed and modified by GT so it definitely does.Not sure if the long one would fit under a GT6 bonnet.

Steve

[DJB350Z]

Thanks all for pointers. I'm learning  about carbs for the first time so knowing to check thinks like throat size is valuable.

The manifold side flange of these are square with four holes. There's adapters in place that accept the 2 slanted studs from the GT6 manifold.

These are being used with a 2.5 PI.

They're in my dad's garage now so will measure up tomorrow. I've discovered a size chart and looking at the flange shapes alone it looks like H6.

Thanks again.

[DJB350Z]

Spent this afternoon lapping in the valves and started fitting the new valve springs with my dad.

Will finish the remaining springs tomorrow, and refit the rocker assembly, which although was in good shape I got a new shaft for because the old was a little scored and I was paranoid about one of the oil holes potentially being blocked.

I also ordered new end plugs for the rocker shaft but the new one had threaded ends with plugs already in situe. Saved us a job!

I picked up a replacement set of H6 carbs on ebay for reasons I'll post later.

Also on order are numerous nuts and bolts aswell as a timing kit including sprockets. I still need a timing cover and crank pulley though. Trying to work out if there's compatible items out there for that.

 

[DJB350Z]

Ok then, need some help!

Unfortunately or fortunately depending on how you look at it I grew up in a metric world which is making my quest to find a replacement stud more difficult than I think it should be.

My manual says it should be 5/16 UNF x 1.31. The places I've looked up quote lengths (1.31) in fractional inches. But when I convert the decimal to a fraction I don't see the result as a common size listed for sale.

So how do I find the correct size stud to buy please, or is it a game of do some sums and find the nearest..?

 

[Firefly]

     So if you are looking for a stud 1.31 = 1-5/16"   you will need to go to 1-3/8".   With studs, setscrews and bolts, all ways go a bit longer, you can make them shorter, but you are ****ed if they need to be longer.  

[DJB350Z]

Thanks! So it sounds like I'll just need to use an imperial to metric chart and get the best I can find in the future.

I'm surprised I'm struggling to find this stud off the shelf from one of the usual suppliers! It's one of the 3 studs that sits in the cylinder head that the intake manifold mounts onto.

[Pete Lewis]

canley list most studs as available 

Cylinder Head : Canley Classics

Pete

[DJB350Z]

Thanks for the link Pete.

[DJB350Z]

Removed the core plugs this morning. 1 of them had a hole in and the others were a bit snotty on the inside. First time I've done this job so unsure if they were that terrible but hey ho - another job done. Here's a photo of some of them, you can see which put up a fight..

Will fit the replacements over the weekend. Unsure it needs it but I'm planning to use a smidge of gasket maker around the seals.

[DJB350Z]

We've been attempting to do the timing on my 2.5 saloon engine that will eventually go into my GT6.

Since we had to reinstall the camshaft we need to synchronise the timing of it in relation to the crank. To prepare ourselves for this I've been using this video as a guide: https://youtu.be/wKoWwOWMpt4

My dad made a homebrew version of the plate, piston screw and dowel pushrod setup and we added a timing wheel to the crank and a dial gauge (thou) to measure the lobe position of the #1 inlet pretty much identically as the video. We're also working with a new chain and duplex sprockets.

At around 27:30 in the video Elin talks about moving the crank to 110° which we have also done. However, after reattaching the chain Elin uses his dial gauge to check things. He measures .005 either side of his lobe's centre point, and divides the sum by 2 to equal 110°. He seems quite surprised about it!

When we did that we got 124.5° so to bring that number down we clocked the cam sprocket 90° anticlockwise, expecting a deduction of 8.6°. Instead, we measured 101° so something wasn't quite right there.. maybe?

I want to know how crucial are these numbers for our Triumph engines? Will I drive myself crazy trying to get the magic number?

When turning the crank it's hard to do smoothly, and our make shift push rod seems to have some variance on the dial gauge as it moves up and down. Ive read that there's some slop in the sprocket bolts, as well as the slack in the chain that I try to iron out after an anticlockwise turn.

I'm trying to be as precise as possible but I don't know if I'm being realistic in my expectation to be 'bang on'?

[chrishawley]

I don't use YT so can't comment directly but to get the ball rolling on some replies ot your question here's some initial thoughts - but I'm working from memory here so please don't take anything as chapter and verse.

I'm not sure I'm grasping the advantage of trying to measure camshaft position directly off the lobes as opposed to using the standard method as per the Repair Operation Manual. I think I maybe correct in saying that on at least some 2500 engine the cam lobes are assymmetrical but don't have any more detail on that.

The ROM method can be summarised as follows:

• On assembly the flywheel should have been marked up with datum marks for TDC on 1 and 6 with TDC determined by dial gauge.

• Once head and valve train are on: Set all valves to standard clearance except 11 and 12 which are set wide (say 50 thou, but exactly equal)

• Set crank to TDC

 • Rotate cam untill valve 12 (exhaust) is just closing and 11 (inlet) is just opening.

• Find the cam position such that, with a feeler gauge, clearance 11 = clearance 12.

• Assemble timing chain using one the four available sprocket positions which provides the closest fit and with slack on the tensioner side.

• Rotate engine a couple of times and check. If ok set the proper clearances on 11 an 12.

• Score alignment marks across both sprockets to aid future reassembly.

I think that method answers the question how accurate the crank-cam relation can be: The greatest accuracy is the limit that the camshaft sprocket allows in it's 'best' position.

What I don't know is how that procedure has to be tweaked for an asymmetical camshaft.

I'm happy for the above to be corroborated or contradicted by other memberrs - this is from memory only.

 

 

 

[DJB350Z]

You're right. According to the manual some 2.5 engines have asymmetrical cams. Mine is symmetrical.

We revised our setup a little because our dummy pushrod wasn't sitting quite vertical, and as it raised up and down it would sometimes twist and both these things affected the reading on the dial gauge.

With version 2 of the piston stop and pushrod measurements became more consistent and we ended up getting the cam/crank sprockets aligned as best we could to 110°.

Following that, the head and rocker assembly has gone on and this afternoon we set about setting the valve clearances.

We've found 3 methods to do this.

1) Follow the manual - we found the instructions difficult to follow presumably because of how we set the timing.

2) The rule of 13 - this was probably going to require the crank to be turned over a bunch of times, more room for error and even simple maths would get annoying.

3) Set each cylinder by firing order to TDC, and adjust each inlet/exhaust pair in turn. This is the method we picked, seemed the simplest.

Having done the procedure for the first time, on my first inline 6 cylinder engine, on my first Triumph and of anything of this type and with pushrods etc. paranoia is setting in about how much play there is in some of the arms at different points in the cams rotation. I understand they're opening and closing so there will be movement.

I took a couple of videos, is this normal?

 

[Firefly]

 

        Something very wrong there......?why not use the 13 rule, couldn't be simpler.

[DJB350Z]

13 minutes ago, Firefly said:

 

        Something very wrong there......?why not use the 13 rule, couldn't be simpler.

This seemed arguably simpler, described here from 19m30s. Happy to try the 13 method if it comes to it though. You think there's too much movement as well in my video?

 

[Firefly]

 

     Yes follow the video....or a simpler method not quite as accurate  but fine for road use is the 7 rule. I.E. number one cylinder valves rocking set number 6 cyclinder valves.

[Pete Lewis]

setting both valves whilst on compression strokes does save turning the engine over too many turns  and can work well  what you have is hopelessly out of kilt 

but get the firing order right  153624 is imperative.... to end up with those excessive clearances  im sorry  your method is flawed you have done something wrong here 

i would think best go back to the 13 rule on the rockers and start again 

Pete

[DJB350Z]

Thanks. We'll have another crack at it then and see if that gives a better result. I didn't feel it was quite right.

[DJB350Z]

1 minute ago, Pete Lewis said:

setting both valves whilst on compression strokes does save turning the engine over too many turns  and can work well  what you have is hopelessly out of kilt 

but get the firing order right  153624 is imperative.... to end up with those excessive clearances  im sorry  your method is flawed you have done something wrong here 

i would think best go back to the 13 rule on the rockers and start again 

Pete

Thanks Pete. Happy to be proved wrong if it means I get a better running engine. 

[Pete Lewis]

yes 0.010" tappet clearance is a lot better than  the   rattling good fit  you ended up with

unless you have a cam lift that needs wider clearance to reduce the lift ??

Pete

 

[DJB350Z]

Followed the book today and I'm feeling much happier with the clearances. I'm really not sure what we did wrong yesterday but something messed up along the way.

Here's another couple videos with the crank in different positions, and clearances set to 0.010".

 

[DJB350Z]

I've been waiting for a mk3 flywheel in the post to replace the earlier GT6 flywheel I previously sourced. Along with that I have a crank pulley and spark plugs arriving shortly too.

Whilst waiting around I got bored and decided to start cheering up the windscreen frame and the top of the bulkhead (unsure of its correct name). I took it back to bare metal and sorted some of the previously applied filler out before cleaning up with alcohol, tack cloths and then spraying on a coat of epoxy primer.

It went pretty well so I'll continue with the lower sections of the bulkhead.

[DJB350Z]

Been a while since I posted. Have been busy but not found time to update here. I've since moved along to the front of the bulkhead and removed the commission plates etc. to tidy up everything.

Amazing that even at this stage I'm finding things to remove still..