The Triumph Dolomite Club - Discussion Forum

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PostPosted: Thu Sep 11, 2014 10:40 am 
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Location: Gapinge (NL)
Technically my Dolomite 1850 has got it's share of new / modified parts in the past years (suspension, gearbox, od, brakes, rear axle) and now I arrived at the engine department. I'd like the idea to install a slightly hotter camshaft.
Found a HR270 on ebay two years ago, but a lack of info about this cam hold me off to install it. This week I saw a Kent cam advertised, but Kent didn´t recognise the cam and couldn´t help me. They did offer me a 284 degree cam for the 1850, with 10,65mm lift. Awaiting pricing at the moment.
My question: any experience with such swap? What should be involved when installing a hotter cam?
For now I have 123 ignition (installed), a HS6 inlet manifold and of course HS6 carbs are on the wishlist. Should I change compression ratio? Should I use modified valves/valve springs (and important: are they available)?


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PostPosted: Thu Sep 11, 2014 12:26 pm 
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Hallo Henk!

I think I have a TR7 manifold available with HS6’s at my parents’ place (Goes, Zld) :D

As for experience: Jeroen had a “hot” camshaft in his LPG injected 1850. His engine also had a higher compression ratio. You can ask him the details of his conversion.

As for the basics of tuning, you might want to read/see this as it gives a good impression how to make a strong racing engine: BCCP Sprint engine preparation

I'll PM you my contact details!

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PostPosted: Thu Sep 11, 2014 4:51 pm 
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There is a guy on here Brian (nutter81) who has done a lot of work on his carmine 1850. I haven't seen him recently though as he has been moving house. I think Jonners may know where he is now and what mods he did to his 1850.
Tony.


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PostPosted: Sun Sep 14, 2014 7:20 am 
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Thanks, I'll contact Jeroen en Brian.
I'd like to keep the original engine in stead of a swap with a Sprint engine. I know of the restrictions with box and axle in mind, and besides it will stay a street car so it has to be driveable in city traffic. Against some advises my brother installed a 286 degree cam in his BGT and is suprised how smooth it still is at lower rpm. Idling at 1000 though.


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PostPosted: Thu Sep 25, 2014 5:29 pm 
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I would be interested to know if you have done anything with the exhaust.


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PostPosted: Sun Oct 05, 2014 9:34 am 
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AlanH, my car has only a rear silencer (Rimmer Bros). It has the standard exhaust manifold, there isn't much room to fit anything else. Then from the downpipe to the rear silencer it has a straight pipe, followed by a bend pipe to get over the rear axle.


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PostPosted: Wed Mar 04, 2015 10:01 am 
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Still have to start this project.
A 284 degree cam shaft from Kent is already on the shelves, like a used HS6 setup and matching manifold.
For now I'm after a cylinder head, which can be prepared with these parts. I found a TR7 head, US spec. The seller speaks of extra holes at the exhaust side which could be blanked off.
What's your opinion about this: does a TR7 head fit a Dolomite 1850? Will the US spec give trouble or is the blanking the only point to work out?

EDIT: Found the answer: larger TR7 combustion chambers reduce the compression ratio, so a TR7 head is no option!


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PostPosted: Mon Sep 07, 2015 8:38 am 
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Finished this project yesterday, changes I made:

- max skimmed (but straight) cylinder head
- Kent DM1 camshaft
- self made 4 points chain sprocket to suit 108 ATDC timing
- lightened flywheel (cutouts)
- Saab clutch cover
- Mocal oil cooler with thermostat
- Revotec electric fan with adjustable thermostat
- moved the battery to the boot
- all small parts were tested and replaced if necessary

I kept the HS4 instead of replacing them with HS6, Jeroen advised me that. Have to retune them properly, at first run the engine ran lean so I have globally changed it to the rich side. Had some pressure to get home before the working day started so will do that this week. Engine runs a bit hotter than before (my guess the tuned head and camshaft are to blame) but it's stable. Have to tweak the electric fan a bit to get the best result.
First run without problems.
Next week Goodwood Revival, and one week later the car has to figure during a wedding! Just in time...


Last edited by Henk on Fri Sep 11, 2015 6:25 am, edited 1 time in total.

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PostPosted: Mon Sep 07, 2015 12:03 pm 
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Henk, why did Jeroen advise against using the HS6s? I would have thought that would be a good idea with your uprated cam?

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PostPosted: Mon Sep 07, 2015 2:17 pm 
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He told me the HS6 would give noticable improvement only above 6000 rpm and less power in the lower rpm-ranges which I'll be using much more. I'm still using the car for daily use and don't plan to use it on track days.
I still have to setup the carbs, the last known setup seemed to lean yesterday night. If the carbs don't suit this engine anymore I still have the adapted intake manifold and two HS6's on the shelf.


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PostPosted: Tue Sep 08, 2015 3:22 pm 
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An uprated cam has bigger overlap so less airflow at lower revs. Less airflow at lower revs through a bigger carb is les mixture and more difficult to set up properly. A smaller carb has more airflow because of the smaller diameter so more mixture and better adjustable. Bigger carbs are better at high revs when the cam is doing it's job. The same as having weber carbs you have to advance the ignition at lower revs and idle because of a bad mixture at those revs. Bigger is not alway's better. (carbs).

Jeroen

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PostPosted: Wed Sep 09, 2015 6:58 am 
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Thanks Jeroen, makes sense after your explanation.

Tuned the engine yesterday as we didn´t have a strobe available at first (mine was in my brothers car...) but now it runs way better. Tuned the carbs also to the richer side. Idling sits at 1100 rpm for now, engine seems to struggle below that. I don't find idle that important but before I managed to get the engine running at about 750 rpm. Maybe the camshaft is to blame here?

Cooling is stable for now, electric fan switching in at lower temperatures for now. Using my dashboard gauge as reference, the engine runs as hot as before.

Have one major leak, which seems to originate from the oil filter bowl. My guess is the seal around the central bolt is to blame, ordered a new one.

One question still: is it OK to keep the crankcase fumes away from the carbs? I have the crankcase breather hose mounted on the subframe, pointed to the road. The inlet on the carbs are blocked. In my opinion the SU's and mixture are unnecessary polluted which the oily fumes from the crankcase?


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PostPosted: Wed Sep 09, 2015 9:18 am 
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Having the fumes under the car is ok. But connecting the two tubes on the carbs wil result in slightly better idle. The rough running at lower idle revs can be caused by an ignition timing that is way off or worn distributor. Very variable timing caused by worn springs or loose weights. Also carbs that are not balanced/tuned well. There is a new Dutch company called Classic Kabelboom Company that is specialised in classic car wiring/producing looms and repairing/tuning '60-'80 fuel injection systems but the owner has some experienence with Dolomites. :wink:

Jeroen

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PostPosted: Fri Sep 11, 2015 9:13 am 
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Would that be by any chance your newly started company? :D

Worn distributor is out of question as I am using a 123 ignition system which functioned perfectly before the operation.

It's down to the synchronizing of the carbs. Will sync them at a slightly lower idle, which is currently set at 1100 rpm.
Mixture is set so that the spark plugs colours nicely grey/brown.


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