Reviving my old thread. As my engine is now consuming about 1.5 litres of oil per 10.000 km and I can't get another engine (and they are also getting into big mielage numbers now) I am doing some investigation regarding the overhauling the engine.
My finding so far are a bit inconclusive as the data on internet is mixed up a bit so would ask for assistance of you, nice people, on the forum.
Firstly, there are two versions of engines in our cars. They both share the same basic architecture but they are not exactly the same. Their designations are MHA and MHB. Both produce 125 bhp and have same capacity (1.7 l, 80 x 82.5 bore x stroke). So far, so good.
1.7 version of sigma engine uses nikasil treatment on bores. That is good and bad at the same time. The good: wear on bores is almost nonexistant. The bad: you can't use the chromed piston rings. If you could, there is a set of piston rings for honda 1.8 engine (A18A) at 80 mm bore D and thickness of 1.2, 1.2 and 2.5 mm. I guess if you machine down the nikasil (not that I propose it!) and you are left with steel liners, this set can be used as it is offered in nominal, as well in two additional dimesnions (+0.25, +0.5 mm).
This is the set that is being offered and advertised on eBay as for puma, but it is WRONG! Chrome rings (1st and the oil scraper) would destroy nikasil treatment.
What you need is a steel rings that are nitrited. They are very shiney (the chromed are matt in appearance). Ford si offering them but the price is OMG. It would have to be the first and obvious choice, but if you know someone who can produce them, they should be nitrited (the 2nd phosphatised) and their thickness' are 1.2 , 1.2 and 2.5 mm (for the last one I am not sure).
The second thing that crossed my mind is to actually have a look at 1.6 rings. They are being produced by NPN and Goetze.
The set from NPN uses forst chromed ring so it is a no go, but the Goetze oversized set (nominal 79.50, this one is +0.50 making it the needed 80 mm) is using the first ring in nitrited form so it would be good to be used in nikasil lined engine. The set number is 08-141307-00
The 2nd compression ring is phosphated and as such again applicable in nikasil lined engine, but its thickness is 1.5 mm. I guess it's usability woudl depend on the pistons you are using and whether there is enough of gap (rings have to move in pistons!).
The oil scraper is chromed so it is of no use, but I guess (again I GUESS) the old ones could be used in conjuction with new compression rings?
Moving onto shells. Here there are mixed informations floating around.
Glyco catalogue states that all of the sigma engines from puma (being 1.4@90 bhp, 1.6@103 bhp and 1.7@125 bhp) use the same main crankshaft bearings.
The journal OD is 48 mm (nominal)
The crankcase ID is 54 mm (nominal).
Glyco catalogue number is: H1100/5 STD
Big end bearings
The journal OD is 40 mm
The conrod ID is 43 mm -> this information applies to 1.4 and 1.7 engines (the 1.7 has forged crankshaft). I guess Yamaha wanted to lower the mass of crankshaft and make engine revvier so used smaller journals and forged them to make them durable enough. Again, this makes sense.
Glyco catalogue number for STD shells: 01-4162/4 STD. Available oversized as well (+0.25 mm). The big ends are offered from Ford as well (at least in theory, I don't know if there are any left on stock).
The 1.6 engine has bigger Big end
Journal OD is 44 mm
Conrod ID is 47 mm
Now, here NPN catalogue differs: it states the MHA engine is like stated already, but MHB has bigger shells (main OD 58 mm, big end 47 as on zetec 1.8 and 2.0). Since right beneath MHB is the silvertop zetec, I guess someone wrongly copy pasted this info and I am inclined to go with Glyco (Federal mogule) information on this matter. Anyway, the bearings for puma engine are obtaineable .
All you need now is set of gaskets and some torqueing information.
Big end is to be torqued 21 Nm + 45 degrees (Ford info). The rest will have to be taken from shawspeed page (www.shawspeed.com)
And the question asked about 100 times: what is the difference between MHA and MHB engines? Still unsure. There are differences in valves, but not by MHA-MHB differentitation, but only on basis of date of production. Again, as Federal mogule (www.fmecat.eu) states, engines after 01/98. use bigger exhaust valves (26 instead of 24.1 mm), and the inlet valves were also slightly enlarged (30.1 vs. 30 mm).
My kind request would be if someone has engine in pieces to try measuring these dimensions stated here to verify them, please?
Ta in advance,
PS. Forgot to mention: 1.4 and 1.6 engines are easy repairable as FM is offering for them everything including pistons
