1592 crankshaft grind specs...

[99ZoomR]

Hi folks.

Last Spring I became the proud owner of a Series 2 Alpine, and am having a good mechanic friend rebuild the engine for me due to worn bearings and low oil pressure issues. However, the machinist doing the crankshaft resurfacing is unable to find the crankshaft "grinding specs" for my 1592cc engine. (variances, radius info?) He said the info in the workshop manual I provided aren't what he needs, so I'm hoping someone on the forum can provide this info, or has some idea where I might be able to find the info he needs. I tried searching past threads and looking at all the tech info I could find, but had no luck.

Thanks in advance for your help!
Len

 

[RootesRacer]

Zoom,

if you provide him with the crank and fresh bearings, your machinist should be able to grind for proper clearance (.0015 to .0025").

The WSM DOES however contain the info needed, though this assumes that the bearing shells are dead on, which is a very bad assumption these days.

 

[99ZoomR]

Thanks for the quick reply Racer! Based on some paperwork I received from the previous owner, the main bearings that were installed before were .20 and the rods were .10. Should I order the same sizes again and will the machinist need to have these and the block so he can grind the crank and then check the clearance? My mechanic was planning to put everything back together once he got the crankshaft back from the machine shop, but if it would be better for the machinist to have the block along with the crank and bearings I'll do that. (sorry for all the questions, I've been lucky enough to not have to do this on any of my other cars...yet) Would it be better to order .30 main bearings and .20 rod bearing? I'm not sure how much grinding they'll need to do to make the surfaces smooth again...

Thanks again...Len

 

[RootesRacer]

Before doing anything, someone needs to measure every journal and inspect the journal surfaces.

If all journals are "in spec" both vertically and 90 degrees off, then I would just get new bearings. If however journals are overheated or scored, you will need to determine the depth of scoring, then choose which undersize will be appropriate. Remember that journals wear the greatest in the plane that the rod imparts load on it (vertically).

Bearings are becoming harder to find in useful undersizes (.010-.030) and some bearings are known to be quality rejects or have shelf rot.

You should always plastigage the final result to make sure that the bearing you got is the bearing you wanted.

Something to consider on the rod bearings is that if you go with chevy rods, the STD small journal SBC bearing is the same as the STD rootes 1592 journal (2.000"). This means if you go with chevy rods at least the rod bearings become a simple buy with a plethora of undersize options.


HTH

 

[99ZoomR]

Thanks! I found out this morning that the shop where I left my crankshaft actually ships it to another shop for crankshaft milling work. They'll send the info from the WSM along with the crank tomorrow morning. The mains all look very good, but there was some minor scoring on the #4 rod journal and even less on the others. Hopefully they'll be able to get the rod journals nice and smooth again. I was planning to get some new rod bearings from Sunbeam Specialties once I know what sizes will be needed and if they have them in stock. Thanks again RootesRacer for all your help! It sure is great to have the expertise available on this forum, along with email info I've received from one of the members who owned this car many years ago. Rick and Richard at SS have also been very helpful and patient with all my numerous 'newbie' questions...

 

[chazza]

RR, as usual you are a mine of useful information - thank you!

Can you explain more abut the Chevy rods please? From what model? Year?

I didn't quite follow your explanation about the little-end size; or am I confusing it with the big-end size?

I can see myself having to a do a bottom-end re-build one day and it is nice to be prepared in advance,

Cheers Charlie

 

[RootesRacer]

RR, as usual you are a mine of useful information - thank you!

Can you explain more abut the Chevy rods please? From what model? Year?

I didn't quite follow your explanation about the little-end size; or am I confusing it with the big-end size?

I can see myself having to a do a bottom-end re-build one day and it is nice to be prepared in advance,

Cheers Charlie

Charlie,
Now you have me confused.

I looked over my two messages and didnt see where I even mentioned anything about "little-end" in them.

The rods are from a 6 cyl chevy, which was based on the V8 small block chevy internals. I forget the specific application, but a google search of this site with "chevy rods" should yield great info.
I seem to recall it was an L6 250CID or something like that.

Originally (like in the 70s) there were folks that used the V8 chevy rods in alpine engines to make stronger bottom ends. The trouble is that SBC rods are narrower than the rootes rod width and the SBC rods needed brazed or welded and machined flat to .990 BE width.

The 6 cyl rod gets around this since it has a 1.000 BE width and can be narrowed (or as Jan likes to do widen the crank journal to the rod).

You WILL have to do something about pistons, in the case of the 1725, IIRC the pistons CAN be shortened for proper compression height (since the 1725 rod is shorter than the SBC rod). Most of us buy custom pistons though.

HTH

 

[65beam]

specs

why is it that if you are rebuilding a stock engine that so many of you need to install chevy rods? why not install new alpine rods?

 

[Bill Blue]

why is it that if you are rebuilding a stock engine that so many of you need to install chevy rods? why not install new alpine rods?

According to Jim Ellis, a set of chevy rods weighs 3 pounds. A set of Alpine rods weigh 4 pounds. The chevy rods are stronger. This is a case where more is not better.

Bill

 

[65beam]

specs

bill,
why worry about a pound of weight when the car is used for normal driving only.

 

[Tom H]

Rootes, I think the discussion about "small end" was the result of this line in your msg : "Something to consider on the rod bearings is that if you go with chevy rods, the STD small journal SBC bearing is the same as the STD rootes 1592 journal (2.000").". I think the term "small journal" was taken to mean "little end" .


Bill and 65Beam, yes, the Chevy rods are a bit lighter and also stronger. But I think they are being discussed here as a solution to the possible problem of finding good bearings for the standard Alpine rods.

When I rebuilt my 1725 I used Chevy rods and I took advantage of the fact that the Chevy rods have a 2.000" big end, which is smaller than the 1725 crank, allowing me to regrind the crank with offset that added 0.100" stroke.

I think Rootes is saying that the standard 1592 crank has a 2.000" big end , which the Chevy rod (and bearings) would fit relatively easily .

Tom

 

[chazza]

Thank you RR and Tom - yes I thought small-end meant little-end Tom is correct, I am concerned about the availability of bearings.

I shall search the forum for info about the rods,

Cheers Charlie

 

[Bill Blue]

bill,
why worry about a pound of weight when the car is used for normal driving only.

The pound is unimportant. Where it is located is important. Remember, that extra pound of weight is flying up and down and around inside the engine, at speeds over 5,000 rpm. I have yet to talk to the owner of a chevy rod engine that was not pleased with the result.

Bill

 

[V6 JOSE]

There is another benefit to using Chevy rods in a 1725. When you make a small diameter journal, you lower the surface speed of the bearing, which helps with bearing life. A ligher rod also helps lower stresses on the bearing, especially at higher revolutions, and makes the engine smoother up top.

Jose

 

[RootesRacer]

unfortunately on the 1725 the loss in crank pin diameter is .125 which does reduce the strength of the crank. the 1592 naturally has a 2 inch pin diameter which makes sense to go chevy rods.

 

[V6 JOSE]

I used to own a crank grinding shop, and I used to grind down VW cranks from 2.10 rod diameter to the 2.00" chevy rod size and the guys used them in heir race engines with no problem. We would also stroke them .100" for more displacement. If the grinder makes good radiuses, the crank will remain sound. What sometimes happens, is that the grinder, for expediency to save time by not radiusing the stone (which also eats a lot of stone, so they leave a square corner,making the crank junk by weakening it.

Jose

 

[Bill Blue]

unfortunately on the 1725 the loss in crank pin diameter is .125 which does reduce the strength of the crank. the 1592 naturally has a 2 inch pin diameter which makes sense to go chevy rods.

Yes, the smaller crank pin reduces the strength of the crank, but that does not mean it will fail. The proper question is "Will it be strong enough?" The answer to that question has to take into consideration the reduced load on the bottom end brought about by the lighter components. That answer is way beyond my capabilities.

However, the empirical evidence indicates the answer is "Yes".

Bill

 

[RootesRacer]

Yes, the smaller crank pin reduces the strength of the crank, but that does not mean it will fail. The proper question is "Will it be strong enough?" The answer to that question has to take into consideration the reduced load on the bottom end brought about by the lighter components. That answer is way beyond my capabilities.

However, the empirical evidence indicates the answer is "Yes".

Bill

Yes, Ive done it on my 165hp engine.

I zero balanced everything, radiused, polished and nitrided the crank.

I wouldnt just slap a set of unbalanced rods on a crank rod journal I took .125 off of. Thats just begging for trouble.

 

[Bill Blue]

Yes, Ive done it on my 165hp engine.

I zero balanced everything, radiused, polished and nitrided the crank.

I wouldnt just slap a set of unbalanced rods on a crank rod journal I took .125 off of. Thats just begging for trouble.

I assume that is a race engine. What would you consider to be appropriate prep for a 5500 rpm,110 hp 1789? That most likely describes the typical build.

Bill

 

[RootesRacer]

I assume that is a race engine. What would you consider to be appropriate prep for a 5500 rpm,110 hp 1789? That most likely describes the typical build.

Bill

If you are going to cut .125 off the pin diameters, I would at the very least weight match the rods, pins and pistons and make sure the journals are well radiused. The flywheel should also be zero balanced.
In short, everything but the nitriding.

Lets remember here that 1725 cranks are iron, not steel.