1200cc five main bearing historic Hillman Imp engine

A friend of mine in Australia bought a super duper interesting historic Imp engine last year.
It has 5 main bearings as opposed to the stock 3 bearing amongst other exotic engineering. I believe it was one of only a few made in the 1960's by Ian Carter for wonderful Rootes Motorsport at the time.
This one is actually 1200cc and i have a hunch it was used by Peter Harper in his Rally Cross days.
Thing is i am assuming that my friend cannot use this engine for his historic involvement in Oz as the Australian MSA have said it is not a stock item...Bah!
Hence he now has to offload it..Not wanting it as an expensive ornament he/we would like to see it used in any category available .

That is the question - Where ?

I have already had info regarding it is suitable in South Africa. I'm thinking it is useable in Germany with the Nurburgring series..Forgotten what they call it!
Still have to receive all the details of spec and price required for it ,but it did cost multi -thousands of pounds.
It is nothing to do with the Coventry Climax 1200cc Elite and so on engine ..Different physical size altogether.Neither is it based on a fire pump engine.

It was sold last year on ebay ,but my mate cannot find the history lesson that came with it. I for one would like to know all that out of much interest alone. Prior to sale it was refurbished by Ben Boult the Imp worker and is ready for use.

Over to you historians!

Edited by mollykeizer, 27 September 2011 - 18:16.

A friend of mine in Australia bought a super duper interesting historic Imp engine last year.
It has 5 main bearings as opposed to the stock 3 bearing amongst other exotic engineering. I believe it was one of only a few made in the 1960's by Ian Carter for wonderful Rootes Motorsport at the time.
This one is actually 1200cc and i have a hunch it was used by Peter Harper in his Rally Cross days.
Thing is i am assuming that my friend cannot use this engine for his historic involvement in Oz as the Australian MSA have said it is not a stock item...Bah!
Hence he now has to offload it..Not wanting it as an expensive ornament he/we would like to see it used in any category available .

That is the question - Where ?

I have already had info regarding it is suitable in South Africa. I'm thinking it is useable in Germany with the Nurburgring series..Forgotten what they call it!
Still have to receive all the details of spec and price required for it ,but it did cost multi -thousands of pounds.
It is nothing to do with the Coventry Climax 1200cc Elite and so on engine ..Different physical size altogether.Neither is it based on a fire pump engine.

It was sold last year on ebay ,but my mate cannot find the history lesson that came with it. I for one would like to know all that out of much interest alone. Prior to sale it was refurbished by Ben Boult the Imp worker and is ready for use.

Over to you historians!

Suggest you look at www.theimpclub.co.uk there will almost certainly be people on the forum there who can help.

Sorry that should have come up as a link, also tried to copy your post to add to the Imp Club forum but that failed as well.... my computer seems very unhelpful today!

Edited by RCH, 28 September 2011 - 11:39.

I seem to recall a unit like this being run in Irish saloon racing by David Hall in a Davrian (Imp-shape). At the time I think it was described as an ex-Harper rallycross unit which had, if memory serves, some kind of French connection. Chrysler and SIMCA were together at that time.........

Presumably there are no more blocks or cranks so if it lets go that would be the end of it ?

Presumably there are no more blocks or cranks so if it lets go that would be the end of it ?

65mm cranks are still available and you can do wonders with a TIG welder nowadays!!


Just going to take the dogs out and post some more news on the engine..
It is indeed number 4 of 6 engines specially made for Rootes in circa 1965!1

I don't want to "put the mockers on you" "(jinx you", in Aussie slang), but years ago at the old Surfers Paradise track we were attracted to a guy preparing a side-car motor-cycle-outfit for a race at the track there by the stupendous orchestra of him "warming" the engine in this outfit . It was ear-piercing and quite amazing, and a bit of discussion followed, with him advising that it had an Imp engine of some sort that he was accustomed to "revving to over 10,000rpm, and it was simply unburstable..."
He then proceded to further demonstrate by free-revving the engine to a shrieking crescendo which was terminated as the engine self-destructed and people scattered as it rained engine shrapnel for what seemed like 2 or 3 minutes....

Many years ago, when rallying an ex-works Gp2 Imp, I got a new camshaft from Chrysler Comps and was told "The power comes in at eight and a half, and the engine goes out with it at nine-two ".
Seems reasonable........

Many years ago, when rallying an ex-works Gp2 Imp, I got a new camshaft from Chrysler Comps and was told "The power comes in at eight and a half, and the engine goes out with it at nine-two ".
Seems reasonable........

Hence the attraction of the 5 main bearings and relative crankshaft.
Imp engines put together properly and properly used usually run at 9000rpm in Sprint races..You get what you pay for.
This one developes max power at 7800rpm..As per dyno 135 bhp..It is in "Rally" specification. I know it is all figures,but Jerry lowered his best personal lap time with this engine at his local circuit by 2 secs.
As opposed to his regular 1 litre unit!!
This was inbetween 2 x 20 minute test sessions.
Add together the historical importance its a jewel of an engine..
Anyhow i didn't ask for all this negative information.I would like to know the history of #4 and what happened to the rest!

It would be interesting to know the bore and stroke sizes to see how it compares with the the various configurations for the Imp motor.
Roger Lund

It would be interesting to know the bore and stroke sizes to see how it compares with the the various configurations for the Imp motor.
Roger Lund

Common measurements are 60.37mm stroke x 68mm bore = 875..Oversize pistons available to give some 900cc. 70 mm pistons from the later B1 talbot block =930cc.
If you have the later B1 block circa 1978. o/s pistons + 30 = 950cc. 72.5 mm pistons can be used in this dry liner configaration also.

Wet linered blocks ...72.5 bore x 60.37mm stroke =998cc. + 60 th(74mm) = 1040cc.

Crankshafts ..A lot of crankshafts were left unmachined on the journals so you ground what come may up to 65mm = 1070cc on a 72.5mm bore or nearly 1100cc on a 74mm piston.

Sometimes with special extra thin wills rings 75mm bore x 65mm stroke = 1150 ish

I think the star engine here has a special crankshaft of 68mm and bore of 74mm hence 1204cc.

Thank you for your interest.

Nathan also developed an 850cc motor for the US IIRC
RL

....Anyhow i didn't ask for all this negative information.I would like to know the history of #4 and what happened to the rest!

Sorry... I thought you may have had a sense of humour...

Many years ago, when rallying an ex-works Gp2 Imp, I got a new camshaft from Chrysler Comps and was told "The power comes in at eight and a half, and the engine goes out with it at nine-two ".
Seems reasonable........

My son ad I have raced Imps in Nordic Historic saloons since 2004 (I also raced Imp Special Saloons in the late Seventies and early Eighties) and a properly put-together Imp full race motor is a jewel. It will run reliably to nine-five and be flexible enough to potter through the paddock witn no vices. It needs a properly stiffened bottom end (a 5mm stiffening plate attaching to the sump fixing bolts, sandwiching aluminum alloy blocks between itself and the main bearing housings.) Adding ARP con rod bolts, JE lighweight pistons and steel con rods allow us a whole season of trouble-free engines, and even at the end of that, a routine re-build shows the engines fit as the proverbial fiddle. With what is available in critical items to day (rods,big end bolts and pistons) these brilliant little engines can be enjoyed to the full, no need for five-bearing blocks imo.
Incidentally, a std crank forging, if purchased with the big ends unmachined, can be ground to a stroke of 65mm which with a bore of 74mm will give 1118ccm. Adding material to the crank to give 67mm stroke gives 1152cc, while going to 70mm gives 1197cc. It is also possible to go to 75mm bore with 70mm stroke which gives 1237cc. While going long stroke will not give a shedload more horsepower, it does increase torque by a significant amount. Otoh, the engine will lose a fair bit of its brilliant willingness to rev.

Sorry... I thought you may have had a sense of humour...

No need to be sorry mate.I'm always upfor a laugh!

Are you a bit sensitive?


Thanks for the post Dr Knutson. Couldn't have said it better myself..
As well the flexibility and lightness advantage the cost of actually obtaining Imp engines was far more economic to other units of the same 1000cc at the time.
Probably not so much now due to re-manufacture. As you know the disavantage was the Rootes/Chrysler/Tslbot people homogating nthe item for FIA use !!

Still waiting for some marvellous historian to come up with the details of these 1 of 6 1965 engines!!

" 1 of 6",sounds a bit like the Star trek Borg science fiction..

I seem to recall a unit like this being run in Irish saloon racing by David Hall in a Davrian (Imp-shape). At the time I think it was described as an ex-Harper rallycross unit which had, if memory serves, some kind of French connection. Chrysler and SIMCA were together at that time.........

Richard,
That very same engine currently resides not very far from you - not doing very much. It didn't have any Simca connection as far as I know.

This is the story as best I know it - 6 No. 5 bearing engine sets were made for Rootes in the early days (1964 or before) by Coventry Climax (or the bit of it that used to be ERA) but not all were machined; at that time Ian Carter worked on them. They had 5 bearing cranks and cams and 'deep' heads with semi-downdraft ports. One of these heads was used by Tiny Lewis on the 1965 Monte Carlo Rally - I think. They weren't used for racing until Frazer wanted a bigger engine when he had some of them machined and put them to good use as the 1001cc engine (Robin Human probably knows more about these than anyone else). Eventually one of them found its way into one of Peter Harper's rally cross cars. Over time all the engines were completed by Ian Carter at various sizes over 1200 and David Hall acquired one of them which subsequently ended up with Nick Humphries and eventually came over our way. It ran for a few events until it holed a piston. There were other big engines made from otherwise experimental blocks around 1986 and some of these blocks also found their way to Ian Carter eventually as far as I know. I'm sure there is much more to this story, I only have part of it and perhaps not in the right order; I would be happy to be corrected. these have nothing to do with the big engines that use a spacer to accommodate a long stroke crank.

Did I read somewhere that Alan Fraser had a special batch of blocks cast in a higher strength alloy to produce an unburstable engine?
(It may have been in Tony Lanfranchi's book?)

Did I read somewhere that Alan Fraser had a special batch of blocks cast in a higher strength alloy to produce an unburstable engine?
(It may have been in Tony Lanfranchi's book?)

This is getting interesting..Much appreciated!

Did I read somewhere that Alan Fraser had a special batch of blocks cast in a higher strength alloy to produce an unburstable engine?
(It may have been in Tony Lanfranchi's book?)

From and old topic…

Did/might/could anyone  check to see if there was any mileage in Duncan’s recall?  Or has anyone come across any more information? It would make for fascinating reading and extension of this topic.

Roger Lund 

Engines don't burst because of high pressure or something, but because of friction which then 'dislodges' internal parts to the point that they go AWOL, damaging the block on their way out. No material will be strong enough to withstand those forces in a practical sense, and even if it did it would be of little practical use since the engine would still be wrecked. Damaged blocks can be repaired with relatively little effort, so it doesn't really make sense to produce blocks able to withstand a blow up, and the downside (weight!!) would be enormous.

More likely they had more ribbing in them to enable them to remain rigid at higher revs and with more power...

Check out Andy Jones' Youtube, he is the go to Imp engine guy in the UK.

Here is his chat with Ben Boult