4.2 and 4.5 ajp

[Toady1]

what the difference in the spec of the two engines? are they the same lump, albeit the 4.5 is a longer stroke, or is it in the bore diameter? or both?

there is a 4.2 cerb in the ph classifieds that says it has a 4.5 crank in it, why would this be so??

cheers...

[350matt]

its not unknown for some pre '98 4.2's to break crankshafts hence the need for the later 4.5 crank which was machined from solid and hence higher quality / stronger the stroke is the same between the 4.2 and the 4.5 its an increase in bore which gives the extra capacity.
The broken cranks originated from a batch of poorly cast cranks on early 4.2's, they very early 4.2's were machined from solid and hence fine and post '98 they sorted out the quality problems with the cast cranks


Matt

[purpleheadedcerb]

Do you know roughly which engine number on the 4.2's these 'early' cranks ceased to exist? I only ask as the one I'm getting is a Sept 98' car but I think was built in Feb.

Thanks

Scott

[Tam Lin]

purpleheadedcerb said:

Do you know roughly which engine number on the 4.2's these 'early' cranks ceased to exist? I only ask as the one I'm getting is a Sept 98' car but I think was built in Feb. Thanks Scott

Hi there, our 4.2 is built in April '97, and it's already one of the later spec engines.

I think there were numerous variations, as early blocks came in several flavours, some with reinforcing webbing to stop them flexing and going bang. There were also high-compression engine versions etc etc. Seems it's a bit of a lottery as to what was used when by the factory, but indicators that can be used are:
1) Does it have the early "noisy" cams?
2) Is the dipstick at the front of the engine (later ver) or half-way down the block?

[purpleheadedcerb]

Thanks for that info. I'll have a look on Saturday when I pick it up. Its done 50 something thousand miles so is it likely that the 'noisier' cams if fitted by the factory have been replaced by now? From what I have read, the earlier cams were a more race orientated profile with a longer duration? I could ask the seller but I don't want to annoy him with yet more questions!


Cheers,

Scott

[longbow]

The later 4.5 cranks are not forged steel items on the whole - they are improved castings. This is straight from Al Melling. It is rumoured some early 4.5'GT''s have forged cranks, and although Al did say some very early 4.2's had forged cranks, his story of the 4.2 running across Europe with a broken crank makes me think maybe not. If you want a forged crank, you'll need to get one from a Tuscan racer AJP or direct from TVR, although I'm not aware of any 4.5 snapping its crank, it is an early 4.2 thing, 96 ones seem common. The stroke of the 4.2 and the 4.5 is the same at 86mm, I'm not sure but I reckon the 4.5 crank has larger diameter journals over the 4.2 - hence why a 4.5 can be fitted to a 4.2 block by line boring.

[ROB1]

Hi, I have a 4.2 cerb 1st registered April 97 (don't know when it was actually built). Previous owner bought car with a broken crank and after talking to John Ravenscroft at the factory proceeded to line bore the block and fit the later 4.5 crank which has larger diameter journals. Apparently John Ravenscroft said about the bad batch of cranks and it was "only a matter of time" before it went bang. Anyway I have owned the car for 12 months and done about 2000 miles with absolutely no problem at all (touch wood). If you want to know more, e-mail me off line and I will put you in touch with the previous owner of my car who carried out the repair. He is a member of pistonheads.
Rob

[PetrolTed]

There was a theory that in more recent years all the blocks were 4.5 litres in capacity anyway as it wasn't economical to produce two different blocks...

[GreenV8S]

Do you really mean forged, or billet? Surely forging would be hideously expensive, I would have thought that machined from billet would seem more likely?

[trackcar]

but it *is* cost effective to produce one block version and different liner versions .. the story looks like it probably came about because of the bearing issues and change up a size on those? ie all later engies had the *4.5* size journals hence being called the 4.5 block? kinda like all new type clutches are the 4.5 type even though they were fitted to all the later models.

some good info on here ..

[dinkel]

4.185

4.280

4.475

never knew there were 3 . . .

[else]

dinkel said:

4.185 4.280 4.475 never knew there were 3 . . .

Thats interesting, the first one is 4 valves per cylinder the other two have only 2.

Is that correct and if so why go to 2 valves per cylinder from 4?

[longbow]

If there is a 32 valve Cerbie out there I'm a Chinaman....... no, this isn't right.... only ever been 2 valve per cylinder. Plus the engine capacities. THe first and last are correct, middle one is new to me..... I don't think the 89mm bore is correct - its 88mm for the 4.2 and 91mm for the 4.5

[JR]

else said:

Thats interesting, the first one is 4 valves per cylinder the other two have only 2.

The first was the prototype proprosed spec. (dry sump)

else said:

Is that correct and if so why go to 2 valves per cylinder from 4?

Yes and Peter Wheeler I believe.

[longbow]

I think the 2 valve setup is the single biggest letdown with the AJP, can you imagine a 32 valve AJP8? Al Melling said he wanted to design the AJP8 that way but Peter Wheeler insisted on a 2 valve per cylinder head, as quote "It was traditional". He estimated a 32 valve AJP8 would be in the region of 500hp

[Toady1]

but it wouldnt have had the instant torque you tend to get from 2 valves per cylinder tho would it.

[dinkel]

Toady1 said:

but it wouldnt have had the instant torque you tend to get from 2 valves per cylinder tho would it.

A Lotus man and Bentley technician recently told me a 2v combustion takes more time so creates more torque . . . TVR is a bout torque so I can understand the decision. The 32v AJP8 is to come is it . . .

OK, A**8 or AND8

Nah, that sound off does it . . .