BN4 Engine Rebuild Questions

[Csarneson]

Guys you have been incredibly helpful in the past. My car was in many pieces when I got it so I am trying to rebuild based only on images in the manual and what I can find online. Thus I have lots of questions. I've searched the forum on each with unsatisfactory results.

1) What holds the rear end of the camshaft in place? I know this sounds like a stupid questions but NOTHING is shown in any diagram I can find. The front end has a plate with a hole in it. My block is on a stand and I don't want to risk the cam sliding out when I rotate the engine.

2) Is there a particular camshaft moly-type lubricant brand I should purchase? I've been using Permatex Ultra-Slick everywhere else but I've heard that it's not thick enough for the cam lobes. My machinist gave me a quart of ZDDP to use in the initial break in as well.

3) How do I know if I can re-use my old early BN4 oil pump? It's the rotor and vane style. Is there a easy way to diagnose a potential problem? I also have a later gear style pump that also seems to fit. It's in nice shape and came in a box of misc parts I bought. Is that a better design? I only have one driving spindle and that's from the original pump and it has some wear on the end. I'd love some advice here.


Thanks so much again!!!
Chris

 

[dcarlg]

Hi Chris.
I'm also a novice currently rebuilding an engine.
1. The cam is prevented from moving to the rear by the rear engine plate.
2. I just bought a tube of assembly lube from Amazon. It's a lithium/moly/graphite grease. $10
3. My research found the vane type oil pumps are slightly preferred for having higher flow. But I have the gear type.
Good luck.
Douglas

 

[Bob_Spidell]

That's a lot of wear on the shaft. I just rebuilt a BJ8 engine with over 100K miles on it and the shaft looked perfect (IIRC). I think you should tear down the pump; I suspect you'll find scoring on the housing and rotor/vane and, IMO, have a machinist repair the shaft or replace the shaft. I can't tell from your photos if the gears on the shaft are worn; if so, the shaft is toast. If my shaft is in as good a shape as I think it is I'll cut you a fair deal on it--send a private message if interested--Moss wants $239.99(!), and it's only for cars from #38263 on (you also need a thrust washer--mine seems to have disappeared).

The rotor/vane type pump is more efficient at low RPMs, but were known to cause excessive wear, failures even, on the shaft and/or cam gears. The gear-type are rebuildable--British Parts Northwest, for one, has kits--but they provide a bit less pressure at low RPMs. Denis Welch recommends their 'high capacity' pump--which I believe is the rotor type--for engines that don't see 6,000RPM, and the gear type for the racers.

 

[Csarneson]

I do see some wear on the gears. It's not a lot but there are definitely shiny areas on the lower edges.

So Bob are you suggesting I use the later gear pump that I have because it's rebuildable? I looked at AH-Spares and their shaft for that pump is $99. I don't believe they make a shaft for the early pumps. It's crazy how reasonable the prices in England are right now!

 

[Bob_Spidell]

That's a good price; I'm beginning to think the 'usual suspects' are really gouging on these. Even DWR has them cheaper (that's where I got mine).

I don't know if the pumps are interchangeable; Moss shows the rotor type for up to BN/T7 up to engine# 29D-H894, and the gear type for later. I've been told the cam and shaft gears were re-engineered when they went to the gear-type pump to eliminate the failures.

Yep, English parts are a downright bargain now--all hail Brexit!

 

[red57]

I agree with Bob, that is a lot of wear on the shaft & I wouldn't be very comfortable using it in a fresh engine. My personal preference is the gear type pump.
Maybe 15 years ago or so there was a lot of discussion amongst racers about the rotary vs gear pumps because the rotary pumps running at high revs (above 6k) were experiencing gear drive failures - also causing premature wear on the cam thrust plate, and DW started offering a needle roller cam thrust plate to compensate for the fast wear. One friend of mine lost the gears on a brand new DW racing cam - I don't think he had more than 4-5 hours racing when it stripped the drive gear teeth off the cam at speed and, of course, bearings and other stuff suffered as well as leaving him with a virtually new and useless 'dry sump' cam.... One racer in the midwest set up a test with the two pumps driven by an electric motor and measured the amperage draw at various rpms and found the rotary required quite a bit more power to spin that the gear type. (I believe this is why they now recommend rotary pumps for street driven cars because they will not likely see 6k or more and gear type for racing at high revs.) Anyway, my takeaway from several folks is that at least part of the issue is that the rotary pumps have (I think) 5 vanes - so for every revolution there are 5 pressure pulses. And the gear type (again, if I remember correctly) have 7 teeth - so for every revolution 7 pressure pulses. Each 'pulse' in effect is a quick load/unload on the gears and blade. So, if a given flow of output, the 'load', for want of a better descriptive, is spread over 7 pulses rather than 5, meaning each 'pulse' is milder putting less shock load on the gears. Add to that the outer ring of the rotary is heavier than the gears, requiring more power to overcome inertia. Don't misunderstand, in a street driven car the rotary are fine, however I think the extreme wear on the blade on your shaft is quite possibly due to these larger loading forces from the rotary pump. Also, the fact that there is better parts/support for the gear type, make me go that way. I have always run mine to 6k and had plenty of oil pressure from the gear type.
I am not any kind of professional wrench and the above reflects just my opinion and recollections - food for thought.
Dave

 

[Csarneson]

I tore apart both oil pumps today. Both were in excellent shape showing almost no wear. Honestly I would have no hesitation using either of them. I did buy a new driving spindle. Thanks for the advice on that one. Shockingly I even found my original thrust washer inside the "mystery bin of rusted bits" that came with my car and was able to clean it up. The oil pumps are exactly the same size and are clearly interchangable. The driving spindle is compatible with both as well. I haven't decided which one to use honestly. I'm probably leaning towards the newer gear design but it's a toss-up. I will probably toss the other on ebay.

Chris

 

[Bob_Spidell]

I was told the 'fix' for the rotary pump stripping gears--besides the switch to gears--was to reduce the diameter of the cam gear by 'removing' a tooth. Hence, the pump would spin slower and reduce the load on the drive gears. If your cam is original it might have the earlier gear design.

Disclaimer: This is heresay, but from some knowledgeable racer types. I have no idea how many teeth the earlier vs. later cam gears have. I just bought a new cam and rotary-type pump from Denis Welch and they assured me there would be no problem with that combo, but they recommend the gear type for engine speeds in excess of 6,000RPM.

 

[Randy Forbes]

As I was to find out when I put a BJ8 cam in the Longbridge engine I've posted pictures of so many times, there is most assuredly a large diameter and a small diameter drive gear on the cam, and a correspondingly small and large driven gear, respectively, on the pump shaft. As long as you use a small with a large, in either combination, everything works fine...

There is however, the little issue of the 100/6 block, that originally had the smaller driven gear, not having a large enough spot-facing to clear the later, larger diameter pump drive shaft's gear.

It's those little things that get you!

Small cam gear/large pump drive gear: