Technical Has anyone rebuilt an HGT engine?

[MattR222]

I am in the middle of rebuilding my HGT engine after the ends went. I keep coming across problems that seem to be caused by the way Fiat built the engine. For example:

Con rods (big end) are not round and it is impossible to get the oil clearances within spec. I would replace them but it seems likely that even new ones would be the same (about £100 each as well)

The new Fiat shells are not consistent within thier own tolerances

The bores are not properly lined up with the crank Ie 3 and 4 are slightly off centre.

The crank it self is to very fine tolerances but the rest of the engine seems to vary.

Has anyone else had this type of issue? Any techies out there that can help?

I am about the put it back together knowing that even with new shells the ends oil clearance will be about 20 micron too large on one axis and spot on on the other axis.

 

[MattR222]

Is no one going to answer? Am I not using the forum properly?

Please let me know if I am doing something wrong, I could do with some tech support.....

 

[richie.guy]

Not many people bother to re-build the engine, I think that's why no-one has replied.

 

[MattR222]

I'm not surprised! Still, the ones in the scrap yards are liable to be just as bad. At least this way I know my engine is good now. Got it back in last week end and it started first time! Just need an exhaust now....

 

[ChrisUK]

Yes the HGT engine is a bit of a biff. its the same unit as the Alfa Twinspark 1.6,1.8,2.0 16v(with the addition of a counter balace shaft) with a difference cylander head. They are renowned for major problems such as bottom end failures of various types. Probably as you say due to poor tollerences on most of the parts (except for crank).

 

[MattR222]

Absolutely! For some reason the crank is made to really high tolerances but then everything else is sloppy! It looks as though they were hoping the crank would pull everything else in line!

I hope to get the car back on the road this weekend, but I am not at all sure that I would buy another fiat.... Still, I'll wait and see, you never know..

BTW has anyone tried to send parts back to Fiat? I bought a set of standard piston rings by accident and am still trying to get Fiat to take them back even though I subsequently spent over £1000 with them on other bebuild parts!

 

[StevenRB45]

My experience of fiat parts departments is that anything you've had to order in specially you can't return for a refund doesn't matter if its been used, hence why I still have a bunch of unused boxed mk1 punto parts that turned up after my car had gone bang! Would have given them to the next owner but forgot

 

[The Sultan]

are the big ends not out of round when cold for good reason ie when they are warm they will be correct due to diferent thickness of metal expanding at diferent rates in much the same way that a cold piston is oval

the cran kis nitrided steel and extremly toughth so would exspect that to be corect

the bores not lining up with crank sounds daft how exactly did you measure that

and do i think the engine desighn is slopy no i'm sure all these things are done the way they are for good reasone only time will tell if your engine is right thou i spose

also if you got a crank and shells do you realise every shell has an exact place every one will be machined to match the crank if you just got some shells do thaey not need machining to match your measurements on the crank

 

[MattR222]

I agree, the whole thing sounds daft to me! The ovality of the rods were outside fiats own tolerances and could not have been caused by wear or stress. My rods are about 20 microns outside the tolerance in one axis and well within tolerance on the other. The bores were also not lined up right with the crank. I have rebored them now to 0.4 over and this has brought them back in line. I'm sure that Fiat must have built the prototype to better accuracy but then it got lost when they started to mass produce.

Still its back together now and I had it running for a while last weekend until I broke one of the lambda sensors....

Sounded sweet as a nut...

 

[The Sultan]

I agree, the whole thing sounds daft to me! The ovality of the rods were outside fiats own tolerances and could not have been caused by wear or stress. My rods are about 20 microns outside the tolerance in one axis and well within tolerance on the other. The bores were also not lined up right with the crank. I have rebored them now to 0.4 over and this has brought them back in line. I'm sure that Fiat must have built the prototype to better accuracy but then it got lost when they started to mass produce.

Still its back together now and I had it running for a while last weekend until I broke one of the lambda sensors....

Sounded sweet as a nut...

it all sounds a bit daft there must be reasons for it so do they actually state how oval it should be at say 20 degrees room temp or what ever it is i notice your talking about 2 axises to measure

it's very unlike fiat they normally make engines that are extremely precise measured buy lazers in factory that also look at the surface and change tools when the finish is getting to bad infact fiat have some of the most advanced engine production facilities in the world they even make 3 story high ship engines and huge diesels for trains like the pendalenos we have here

 

[MattR222]

I'll give you an example:

The con rod caps do not have dowels like most other engines. Instead they rely on a shoulder on the bolts to line everything up. So when you start to tighten them there is a chance that the cap can be out of line by up 4 thou. If you try moving the cap before it is tight it moves from side to side. If they had put a dowel in there this could not happen.

When I bought the new pistons they came from Fiat with rings already on them. Just to check I had them measured and gapped. They were out of Fiats own tolerance!

I'm not at all impressed with Fiat design, the variator problem is further evidence. And I checked the service history of my car, it had always been done by Fiat main dealers, and not once had they used the right oil!

I hope when I get the car going again it will have been worth it...

 

[DaveMcT]

An old post but any news on how the engine performed etc after the rebuild?