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Cheap 1275 rebuild

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Guys, this is a tremendous thread. I'm on the fence right now myself- rebuild my 1098 on the cheap and see how it goes, or go all-out with a pro-built 1275.

After reading this stuff, I'm leaning towards cheap!
 
If you do not mind pulling the engine out and redoing stuff later ... sure. For me, tinkering with the cars is as much fun as driving them, so another engine pull is no big deal. But a budget engine refresh is not a fit and forget.
 
Trevor Jessie said:
If you do not mind pulling the engine out and redoing stuff later ... sure. For me, tinkering with the cars is as much fun as driving them, so another engine pull is no big deal. But a budget engine refresh is not a fit and forget.
Click to expand...

I'm with you on the tinkering. "Tinkerability" is a big part of the Spridget appeal.

If I depended on my Sprite for daily transportation, I would not take the chance on a cheapo rebuild, but for something that I'll be lucky to drive 2000 miles a year, it's tempting.

And if it blows up, I'll buy a 1275 and do it right.
 
I find this discussion very interesting and informative. Lots of the terms and nomenclature associated with pistons and bearings are easy to read, but harder to understand fully. I pulled up this website and learned a lot about how and why things work. I may be faced with finding rings that meet my needs outside of the 'normal' channels and this site helps a lot.
Rut

https://www.hastingsmfg.com/ContentData.aspx?Contentid=82
 
I have yet to rebuild an A-series engine that didn't have excessive gaps/wear in the ring lands, so I <span style="font-style: italic">always</span> use new pistons. Seems like too much trouble to fuss with finding rings that will work and having the grooves resized. I guess it's a good enough solution if you're on a budget, but personally, I hate doing the same job twice.

Regarding the crank, if it hasn't already been mentioned, if the engine has, as you state, "little wear" and was well maintained, Using new STD bearing shells is fine if journals are still in tolerance, however, I'd recommend you have the journals polished first. I don't think that's ever cost me more than $25-$50.
 
Gerard,
Point taken and I will take everything to my friendly, local, machine shop where the owner is restoring an MGA and understands what to look for. I will let him decide if my work is 'good enough' and if the crank, etc. are OK. I have a modified 1275 in my BE currently and would like to rebuild the 948 as a good running 'back up' engine just to see if I can do it. It's bored out .040 over and the only pistons I have that fit are the Jahns domed type. I want to reuse what I have where resonable and prudent, just like I did on my '67 TR4A in '69, and hope I get the same results. I think I had 1 JC Whitney piston and liner in that car and it ran great! I like the challenge and the fun of doing it myself and if it works I'll be pretty happy, if not, well I can pay the man twice. This forum is great for providing knowledge and inspiration as well as a shoulder to cry on.
Thanks, Rut
 
Rut said:
Mike,
Looked at the pistons and measured 1 and they look pretty good. Very sharp edges in the ring grooves and clean. The measurements are:
Top ring groove .090
2nd ring groove .090
Oil ring groove .151

Rings removed from pistons:
Top ring .061
2nd ring .061
Oil ring .123

This 948 came dissasembled and in a box and the PO said it had a 'seized bearing', but the bearings and journals look really good. Several of the rings still on the pistons are broken, but look new otherwise. The're .040 over and the gap while in the bore looks excessive. I would like to buy .060 over rings and file to fit or get the proper rings in the first place. Like Fred, I'd like to do an economy rebuild.
Thanks, Rut
Click to expand...

Don't think I've ever seen a BMC piston application with compression rings that wide in that bore size. Something is going on with those pistons. In the old days, some of the ring companies made repair inserts to fit pistons that had to be machined. This would repair worn out grooves. Usually for old American sized engines.But that doesn't sound plausible for the this situation. Stock ring size was 0.71 compressions and 0.125 oil controls. Not sure what has been done to your pistons. I don't think its going to be a good idea to try and use these pistons. Rings would be a real challenge to find. The oil control is the only measurement near a width I've seen used before. Some 948 pistons by Cosworth used a 4mm ring. The 40 over is close enough to stock 1098 that a replacement ring for a 20950 Hepolite piston might be made to work. But to me, a more practical of a solution is going to have to be identified.

Mike
 
Mike,
The pistons are Jahns, 273 casting on the inside skirt, 3 ring machined style. The ring grooves are very sharp and there is no carbon anywhere to be found other than a little discoloration on the dome. All in all, pretty good shape. I just miked them and they actually show .156 for the oil grooves, .097 and .098 on the top and 2nd groove with the mike vs feelers. The groove depth on the oil groove is .144 and .125 on the 2 compression rings. Someone somewhere along the line said this engine had been raced, but I don't know it's history, just what the LDPO told me.
Rut
 
My appologies to Fred for screwing up his post. Sorry Fred!
Rut
 
Fred, funny you should metion oil pumps, if the pump is like the one on a Healey or TR and in decent shape you can carefully take some of the wear out o it, the gears or vanes on the pump wear slightly away from the pump body and you can't fix that, but you can fix the end float or the difference between the ends of the pump and pump body but sanding the pump base plate or pump body to take up any wear. This is a great DIY cheap fix that works and can add 5-10 pounds of oil pressure back.

My experienced mchine shop guy said the old British motors use better steel than the new stuff, I have never worried about replacing head studs and rod bolts as some preach, and never had a problem, this is for street motors, might do it different for racing.

But yes, new rings bearning, oil pump refresh, rocker arm refresh. If you really want to get into DIY and cheap, how about a home valve grind used to be pretty common, but I have to admit I have never done it. I would probably send the head out for valve work if it were needed.
 
Rings and bearings are fairly cheap and if the motor doesn't have many miles on it, you should be pretty much up to snuff. Also a timing chain is real cheap for the a series as well, so throw one of those on there. Take your time with those 4 ring pistons and don't break one, if that is what it has.
 
Hard to say how much "out-of-spec" is still useable. To make a long story short, when I got my Prefect, the PO had disassembled the engine. I found .030 cylinder taper in all 4 and the babbit rod bearings were so loose he had actually filed the cap down to close the gap some. I added new rings and a hand lap valve job, reassembled and drove it. It made a lot of clatter (sounded like the pistons swapped holes every rev or two) and did smoke a bit but we drove it as a second car for 3 years and probably 10K miles. YMMV. I probably would not do it that way again.
 
Wow Bayless, .030 taper in all 4 cylinders and it still ran for 3 years without a rebore?
Well if that's possible, my 1275 should be super in comparison.

Fred
 
The thing that amazed me more than the cylinders was the rod caps the PO filed to oval shape. The car had no oil pressure gauge so I don't know how bad it was but I would guess really low if any at all. I think you'll get some use out of yours but don't expect it to last forever.
 
Apologies to Fred for all the discussion on the Jahn's which detracted from his intent to get input on a "Bargin" rebuild of his 1275.

So, I added a new topic on the Jahn's Pistons. Will go there to post any new information.

Mike
 
Hey MIke and Rut, you boys have educated me on piston stuff I didn't know, so it's all good!

Fred
 
there is a article in practical classics magazine this month on how to rebuild A series with loads of images
check for it a bigger magazine shops its a UK publication

the cool factoid i learned is a BMW KI motorcycle head and fuel injection fit

ohhh
cheery
steve
 
Steve,
I checked the website and there is a list of contents for the September issue of Practical Classics, but no mention of the A series rebuild. Is it a different month?
Fred
 
In the interest to fairness I’ll play the devils advocate about cheap rebuilds. Here in the photo is a learning experience that will cost you sweat equity as well your cold hard cash. So, in my experience if you cut corners truly expect to pay dearly on the other end.
 
BluMax
is that a rod bolt?

Fred
 
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