Club Triumph

Hey all.
After finally solving my high end misfire issue Ive had for a long time, Ive finally decided to bite the bullet and give the engine a rebuild.
I dropped my engine onto the shed floor today which wasn't too big of a deal. Now I just need a helper to get the bonnet off and then lift the car higher so I can pull the engine out from underneath.

As for the rebuild, Ive got two options
1: refresh the current 2.5 I have. I think it might be ok with a hone and rings, and have the head ported and skimmed. It's all balanced so it revs very nicely, it just lacks the compression it needs to go as well as it sounds. I'll know what Im looking at when I take the head off.

The second option is to go with a 2.7 block that I was given! It has Mazda pistons and has had a double thrust bearing mod carried out, and the bores look to be in really good condition.
The bores are 77.5mm as far as I can measure, but it's a recessed block- I cant find a head gasket that says it will do the job. It has been decked pretty severely to match the piston height (engine number is gone) and I dont know if the recess is what was left of the original or it has been re cut. What is strange is the head gasket seems to be a flat block style. Anyway, for me to use this engine I think Im going to need to get it decked so the recess is completely gone and then get the pistons machined to suit and use a big bore flat block head gasket. I would really like to go with the 2.7 as it has had a lot of money spent on it at some point. Strangely the crank, rods and pistons dont seem to have been balanced. I think it is a cross drilled PI crank like my 2.5 but I will have to compare both- from memory it has cross drillings in some but not all the main journals.The head on this engine has had hardened exhaust seats and 3 angle inlet seats, and by the looks the second biggest valves that Witor sells. I cant imagine you could go too much bigger as they nearly touch anyway. The combustion chamber is standard size, as in it hasnt been widened to suit the bore and it is a pretty thick casting. I think it is a 2500 TC head from memory, not skimmed.
This engine would cost me a lot more to get going properly than the 2.5 but from reading about 2.7s sounds like it might be worth it. I may be able to use the balanced rotating parts out of my 2.5 with this block, rods and pistons.
As for the cam, I have a tr5 in my 2.5 and it goes really well, pulling to 6000 rpm, which I cant see myself going much past. If it is still in good nick I will be looking at using that in either engine. The 2.7 has a PI 132bhp cam in it which also looks in good condition.
I dont know what the story is with the 2.7. The guy who gave it to me said it was "Tired" and needed rebuilding. He was right but it doesnt seem anywhere near as bad as I would have though. There are no lips at all on the bores and most of the cross hatching is clearly visible. It looked to have been using lots of oil and all the rings were stuck fast. I dont know but my guess is that it was not run in right and the bores glazed. There is a small patch of what I think is pitting in one or two bores from bad storage and one bore has a scratch where one of the oil ring tips was for some reason rubbing. I'm hoping these will hone out, but I'll speak to the engine builder and see what he reckons.

This will be my first rebuild and I find it very daunting, but it's something Ive always wanted to do.

Cheers
Josh

Hello Josh,

regarding cross drillings, they are only on the big end journals. As you say you are going to take it to your engine builder, then you will have a better idea as to what you need to do.

Alec

Thanks Alec. Im pretty sure my 2.5 has cross drilled main journals as well. Anywaay Ill find out for sure soon

Don't forget that a proper PI cross drilled crank is also 'long back' in that the flywheel mounting 'boss' is 44mm using a flywheel with a 9mm deep recess.  The later 'shortback' type have a 28mm boss with a 25mm beep flywheel recess.

MUT

Hello Josh,

the mains drillings are those that go down the webs and connect main and big end journals, but they are not cross drilled as the big ends are. Worth checking the big end journals to ensure the brass plugs are firmly in place.

Alec

Quoted from josh18

After finally solving my high end misfire issue Ive had for a long time,

Quoted from thescrapman

Did I miss what the cause was??

Last I picked up was a coil failure, but the mis-fire was still there afterwards.

Cheers

Thanks guys. Alec I looked up cross drilling last night and it's not what I thought it was. I thought by cross drilling it meant the journals were drilled through, not that the mains and big ends were joined by a passage. I'll check out the crank I have- I was told it was cross drilled. Does anyone have a pic of the brass plugs I should be looking for.

Ted- Thanks mate. I have heard of long and short back cranks but didn't know how to tell the difference. I'll check it out. Does anyone know the numbers I should be looking for?

As for the mis fire, I solved it but because I did three things at once I dont know for sure what it was. I changed to new CW red valve springs- these all seemed longer than the ones that came out, some more so than others. While I was at it I also re did the tappet gaps- some of these had closed up a little bit but nothing too bad. I also set the plugs back to the standard gap. I had tried lots of different spark plug gaps much earlier on and none solved the mis fire but it ran the best with a pretty large gap. My theory is that this was drawing the mos current from the dying coil and getting the best out of it. Now with my new 12v coil it seems to go better than it ever has with the standard gap. I have read of big gaps causing high rpm misfire so this could have been a cause. Im probably leaning towards this as the cause as there was no damage at all on any of the tappets, valve tips or springs, which I have read goes with valve bounce.

I gave it a pretty good thrashing just to make sure- I didn't really believe it at first! I will now pull through to 6200RPM and still wants more but I daren't give any more. FInally the header can work like it should!

Glad you solved it - as they say 90% of Lucas injection problems are the ignition

I have large bore gaskets if you are stuck

Thanks Andy. What do you think about the recessed block? Should I get it and the pistons decked or try to use a big bore recessed gasket? The one from WBC say you can only go to about 76.5 or so with a recess.
I also think I read you said you can leave the pistons a certain distance proud of the deck because of the gasket thickness. I that right?
Cheers

The engine is now out. I will need to make a better trolley for it to push it back in though, as the castor wheels of the one I made all just collapsed. Lucky I had a lot of cardboard under it- I had to drag it out with the car!

Quoted from josh18

Thanks guys. Alec I looked up cross drilling last night and it's not what I thought it was. I thought by cross drilling it meant the journals were drilled through, not that the mains and big ends were joined by a passage. I'll check out the crank I have- I was told it was cross drilled. Does anyone have a pic of the brass plugs I should be looking for.

I'm no expert on these engines at all Josh, but as a rule of thumb I'd be surprised if it were okay to leave the pistons proud of the block, even with a thick gasket. With high rpm the rod's will stretch, at which point you may find a touch going on with the valves or head, depending on exactly how much the block / head have been decked.

Thanks guys.
Rich, I did a fair bit of research before I built the header and also used a pipe length calculator. It all basically pointed to having the collector as far away from the head as possible to move toe torque down the rev range. The calculator I used also said to make the primaries always a set length- from memory 14 inches.

I'll check out that crank when I get it stripped down- let's hope it is a goodun.

Well, ive got the 2.5 fully out now and stripped it down to a short block. So far Im really impressed with how good it looks. Much cleaner inside than the 2.7. This block has also been decked flush with the pistons which Im really happy with and has .020 over sized pistons. To my surprise there seems to be no lip at all at the top of the bore and cross hatching is still visible. There are some marks on some of the bores which look like where the ring tips have been but dont seem to be able to be felt with the fingernail.
As for the head- this has lots of potential. It looks to have been mildly ported and the inlets at least are really nice and smooth. It has the same size inlet valves as the other head but the next size up exhaust- pretty much touching and I dont think Id be able to get a hardened insert in the exhaust. The seats dont look too bad either- just need a three angle cut and a lap I reckon. The one inlet I took out needs a new valve guide, no big deal. It even looks to have had some work done to the combustion chambers- opened up around the valve area. I will have to work out the chamber volumes to get it skimmed or if it needs it at all.
When I get myself an engine stand I'll get the rest apart but I dont expect too many surprises there as I have had the main caps off at least before and the journals have always looked good.
To be honest I'm surprised how little wear there seems to be- I regularly drive this car really hard. The only thing is the crank end float is always bad. I replaced the thrusts not too long ago but the float just comes back. I'll definitely be getting the rear main modded to fit the extra thrust shell.

...

About 15 years ago I was helping the local mechanic overhaul a highly modified Holden V8 racing engine and this engine had separate fire rings with a gasket cut clear of the rings.
He eventually sourced some replacement rings, but I know not how.

The car was an old, factory built, Group A, Bathurst race car.  (Group A evolved into V8 Supercar category)

The only references to this type of set-up I have found on the net are for fairly large diesels.

Possibly this approach could be used to save decking that recessed block if suitable ring size could be found or made.

The rings that came out looked like thick copper wire but I did not see the replacements as I was not there when he re-fitted the heads.

Mal.

Josh, have you considered boring out your existing engine to fit the Mazda pistons?

Quoted from junkuser

About 15 years ago I was helping the local mechanic overhaul a highly modified Holden V8 racing engine and this engine had separate fire rings with a gasket cut clear of the rings.
He eventually sourced some replacement rings, but I know not how.

The car was an old, factory built, Group A, Bathurst race car.  (Group A evolved into V8 Supercar category)

The only references to this type of set-up I have found on the net are for fairly large diesels.

Possibly this approach could be used to save decking that recessed block if suitable ring size could be found or made.

The rings that came out looked like thick copper wire but I did not see the replacements as I was not there when he re-fitted the heads.

Mal.

Thanks Nick.
Looks like they could well have been.
Interesting that they were used in Coventry Climax engines in the Imp.
Mal.

Mal, thanks for that. I did read about a similar method somewhere but I reckon getting the block decked would be easier/ more reliable.
Nick #1, yeah I did consider boring the 2.5 to fit the Mazda pistons but I still think skimming off the recess would be easier. I think if I bore out the 2.5 block I would go to .040 or .060 over sized triumph pistons. Still get a capacity increase but keeping it all Triumph makes it all so much easier.
In reality though I think I'm going to do like Nick #2 said- hone and re-ring/ shells and have the head skimmed to get the compression up to 10.5:1.
I'll keep the 2.7 engine for a future build I think.

About shells, I bought Chris Witor's last set of Vandervell VP2 main shells and just got them yesterday. I bought standard size as that's what I've got in at the moment and the crank wasn't showing signs of wear last time I looked. They seem to be so hard to get hold of I thought I'd better buy them before someone else and if the size is wrong so be it. Only issue is that they look to have gotten wet and a fair bit of the steel on the backs is rusted. My plan was to give em a wet and dry sand to get rid of the rust. Is there any issues with doing that?
Cheers

Personally I would stick with Triumph sized pistons despite two of my engines being 77mm bore - headgaskets are very expensive and  Racetoration , Wishbone and Greg Tunstall supplied ones have failed on me or friends fairly recently. Racetorations ones had a large batch of poorly made ones where the fire ring had no support , Wishbone had an issue with bore centres out of place (and now doesn't want to talk to me after supplying 10 useless gaskets) and Greg Tunstalls supplied one about 10 years ago that looked to be made of cornflake packets and ally foil - I refused to fit it but Humph did - it failed in a week. His may be better now as he made a lot of 2.7 engines and I may have been unlucky.
Gareth Thomas got me 6 made as a one off(?) in Germany and these seem OK - but the availability of decent NOS gaskets (don't mention the asbestos word) means it's all a lot simpler to stay at +0.060" or less

Thanks Andy I reckon that's the way I'll go (Triumph). Really would I notice a difference between .020 and .060 oversize?