The Triumph Dolomite Club - Discussion Forum

Hi
I have a Robin Hood based on the 2l Dolomite Sprint the slant 4 engine.
Bought it some years ago and in that time it's only done maybe a 100m. Wasn't completely happy with the build quality so put it in the garage where it was used by the wife as a shelf.
Anyway recently retired so looking for something to so do dragged it out the garage and was going to do it up.
Only thing now is that cylinders 3 and 4 don't seem to be performing. In that when pull leads off 3 and 4 it hardly splutters.
Hmm must be the carbs so set about tuning them up. Runs better but still not happy.
Today did a compression test and cylinders 1 to 3 read 175psi but cyl 4 only 75. Don't sound optimistic does it!!
Poured oil into cylinder, tried it again and the reading nearly went full scale.
In the absence of a leak test I'm guessing rings in 4.
What are the chances of pulling the head off, bearing in mind the head has been on there for 40 years. Advice from my local garage is the studs are likely to be seized and no chance.
Is there any chance of removing piston out the bottom end?
I am not 100% sure it didn't have this problem when I put it away.
Another problem I have is the thermostat housing has almost been eaten away and the narrow pipe up to the header tank was blocked and I would like to replace it as it's leaking. Can't get one from Rimmers anyone know where I can get one?
Would welcome any comments good or bad.
Cheers Al

Welcome, you have come to a good place.

Your garage has done the Sprint engine a disservice; many do! All 10 head studs and bolts on the Sprint are protected under the rocker cover, so there shouldn't be a problem. The 1850 and Stag are a different matter as one bank of fixings on each head on those cars are exposed and yes they can seize. I've only known one stubborn Sprint head and that had been critically overheated.

Your diagnosis sounds correct to me.

I can supply you with a good second hand thermostat housing; is your's early, ie with the outlet to the expansion tank arcing over other unions, or late, having a horizontal spigot to connect the expansion tank hose to?

Ditto what Alun said. I have stripped dozens of Sprint engines, some have been sitting for 20+ years. Never had a problem removing the head. No chance removing the pistons from below.

Welcome to the forum. You have indeed come to the right place. There's a wealth of knowledge and experience on here. Get the head off first and then you will know better what the problem could be. It could just be the head gasket that has gone. It might be possible to remove the pistons with the block in situ but they would have to come out from the top. Whereabouts are you from? Maybe there's somebody local to you who can help.

Let us know how you get on.

Hi Guys
Thanks for the quick replies.
Great advice and given me the confidence to pull the head off for a look. Was a bit nervous as the thermostat housing bolts sheared like carrots.
Also thinking of changing the valve seats as she still runs on lead additive. Any idea what money might be looking at?
Xvivalve thanks for the offer the pipe up to the header tank is horizontal. If you have one to spare let me know how much and I will be glad to take it off your hands.
Was a bit shocked to find the header tank was full but the engine was almost empty.
The lads round at the garage are x BL and know them from the days when I had a Metro.
Thanks again for the help will keep you up dated as work progresses.
Cheers Al

You do not need to touch the valve seats, it is an aluminium head therefore already has hardened inserts. Just use unleaded with, if you choose, an octane booster.

Your thermostat housing doesn't look too bad? I have sent you a PM nevertheless...

Alun, I was going to say the same. You can use 98 RON unleaded which is the nearest modern equivalent to 4-star as an alternative to octane booster. It sounds like the guys at the garage knew these cars back in the day if they were ex-BL. Have you considered starting a thread in the resto section documenting your progress?

Let us know how you get on.

Thanks for the info about the fuel. Leaded was still being sold when I got the car and never raised the question.

Ok today rigged an airline to no4 plug hole and blew air down with the piston at top and could clearly hear air coming out the oil filler.
So that kinda confirms a problem with the rings.
Have left it with the exhaust manifold studs soaking in penetrating oil.
Also filled No4 with oil to let it soak the rings just in case it's a stuck ring.

Will post further as it develops.
Cheers Al

I've bust the rings in a couple of Sprint engines. Both times it was because of pinking: once the timing slipped badly going over Kidstone pass into Bishopdale; once I put ordinary unleaded in and though I'd get away wi' it, but didn't. In both cases the lands between the piston rings had also gone, so it was a set of four pistons and rings - not cheap, well not in Yorkshire any road. I think, in one case at least, there was a piston or two that wasn't obviously bust, but I slung 'em anyway - if they'd been strained that badly, they wouldn't be worth keeping.

If you can get the sump off (no idea what subframe/chassis the Robin Hood has), the pistons and rods will obviously come out through the top. However, in both cases, the garage that did mine fitted new shells without re-grinding the crank. And in both cases the bearings failed fairly soon thereafter - one a big end, the other a main bearing.

I've since been told that fitting new shells on an old crank, however carefully measured, etc., is really, really bad idea. somthing to do with "ovality" was one suggestion. I've also been told that if you put the old ones back exactly as they came out, that's ok. But I have never tested that theory.


I also agree that they're fine on super unleaded. I have run several of these engines for tens of thousands of miles on super unleaded, much of it from ASDA, and never seen any problems with valve seat resession. Had the valve springs go once, but I think that was to do with an over heavy right boot (I wear what my eldest daughter [14] calls "old man's shoes" these days, and the problem's never re-occured).

Graham

Well after a lot of swearing, bruised knuckles and copious amounts of tea got No,4 piston out.

Found the scraper ring had broken into 3 pieces and a chunk of the ring as well.

Had a look on a well known web site local to me and nearly had grabbing pains in the credit card area.
Anyone know where I can obtain piston and rings at a reasonable price?

Cheers Allan

When I've had a problem like this in the past I have gone down to the local engine re-con place with the pistons / crank and asked what they can do. They often have NOS bits in their stores or know where they can get them. They then grind the crank / supply bearings /fit rings to suit. I have some contacts in Berkshire if that helps; Near Reading. Is that local to you ?
Tony.

This thread may help: viewtopic.php?f=4&t=29390

But that's probably only the case if your replacing the set: I would consider replacing the set of Sprint pistons with a set of TR7 ones (with modified valve cut-outs for sure, if I was starting with new) - I have a history with Sprint pistons (there's a long sob-story about it somewhere), and have been worrying about this issue for a while. But even I wouldn't put one TR7 piston in with three sprint ones.

As to the question of whether you should replace just the one that's showing low compression or do the lot anyway: That, I think, depends on the cause.

If it was pinking, I would certainly think damned hard about the risk some or all of the other pistons are damaged, waiting for the lands to give and break the rings, about the effort in putting it all back together, and about then having to take it all apart to do the rest vs. the cost of three other pistons and doing them all while they're accessible. Indeed, if it was any cause other than a weak component, they've all been stressed nearly the same, or should have been. So I would worry, lots, that they are all suspect. Still, if you've more time and knuckle skin than cash, it may be worth the risk.

You could pull the others and look, though I don't know how reassuring a visual inspection that showed nowt would be. And their being out - or there being owt (to see) - would only make me feel more like putting new ones back.

Graham

I agree with Graham and would suggest that this is detonation related and the consequent imminent failure
of other pistons is pretty likely.

I certainly would be having them all out and VERY closely inspected at the very least.

Jonners

Hi again

Now the part no. on the piston face is 1D19 S29A+.508. is this oversize?

Thanks for the advice. Will have the others out for a look but might struggle with replacements.

Cheers and thanks again for your help.

It is 20 thou over sized.

I have known folk suffer detonation previously and replace just the damaged piston, and that is on regularly used cars too. You just need to match the weight and type. If you look up the skirt, you should see the maker's name...

I have a few odd s/h spare pistons, I'll see if I can match it for you...