Honing cylinders with engine installed in the car

[engineman]

I am in the process of removing the existing low compression pistons currently installed in the engine and plan to install new high compression JP pistions which have been lightened by Billcar Engineering in Shrewsbury, the engine has only completed 3000 miles since a rebore 2 years ago so I should not have a problem with cylinder wear, has anybody undertaken this piston replacement activity and could advice me on any pitfalls involved with the honing process and with keeping the crank clean, I have ordered a honing tool from Frost and obtained the appropriate honing oil.

[surreyone]

Hi Engineman,
I have been thinking about changing my low compression pistons for HC pistons but I was worried about the extra weight of the pistons. Anyway, please keep us all posted with your engine up grades.

Thanks & regards
Colin

[nib]

Is it worth all the trouble if the car is running ok? What sort of increase in power are you hoping for?
Im interested as there was only a 1 bhp increase from a Mk1 engine to a Mk2 engine.
Mark

[engineman]

Hi Engineman,
I have been thinking about changing my low compression pistons for HC pistons but I was worried about the extra weight of the pistons. Anyway, please keep us all posted with your engine up grades.

Thanks & regards
Colin

Thanks for the interest, the JP pistons were 600grams without gudgeon pins and rings compared to 420 grams for my original AE pistons, Billcar were able to reduce the weight to 450gms,which is much more accepable, I plan reduce the weight of the conrod as much as I can to compensate for the 30gms difference. Its going to be a bit of a juggle to match all the pistons/conrod assemblies so that the recipricating weight is the same for each and the rotational weight of the big end assembly is the same for each to within 1 gram.

[StagnJag]

I didn't think HC pistons were available any more?

[engineman]

Its a bit of an engineering challenge, last year at the Enginuity day in Acton I was little bit miffed that a bog standard stag with H/C pistons nearly matched the power output of my car which has a modified Holley fitted / four branch tubular manifold and various other modifications and was perfectly tuned at the time, I want to see what the difference these pistons make.

[Ian Durrant]

I didn't think HC pistons were available any more?

They aren't. I think the current pistons can best be described as *not* low compression pistons

[engineman]

I didn't think HC pistons were available any more?

They are available through Thorntons in Shrewsbury and are manufactured by JP pistons in Australia, the drawback is that they are nearly 50% heavier that the County Low compression pistons and they are much more expensive, you have to be a bit cranky like me to go to extra expense of buying them and having them lightened. the finished product however does look good but the proof of the pudding is when I get the car back on the road.

[surreyone]

They are available through Thorntons in Shrewsbury and are manufactured by JP pistons in Australia, the drawback is that they are nearly 50% heavier that the County Low compression pistons and they are much more expensive, you have to be a bit cranky like me to go to extra expense of buying them and having them lightened. the finished product however does look good but the proof of the pudding is when I get the car back on the road.

I think the idea is very interesting and I for one can not wait until you get the Stag back on the road. Please keep us informed about the power increase and what you think about the way the car drives on the road.

Regards
Colin

[marshman]

I've not done it on a Stag engine but I have replaced the pistons on my land rover 2.5TD engine in situ without removing the crank. In that case I covered the crank journals with clean rag soaked in oil so that it was sticky. I also masked off the top surface of the block to stop any debris falling into oil and water ways. I then honed the cylinders in the "normal" way. When i had finished I cleaned the whole lot up starting at the top with lashings of petrol to wash all the debris off. Lastly i lifted the oily rags off of the journals and gave the crank a thorough rinse as well. then i blew the whole lot out with an airline.

Engine still ok years later.

I assume you know how to get the correct honed finish - what speed to have the drill on and how fast to move it all up and down? I was told do it all at low speed and move the drill up and down quite fast to get the correct angle on the honing marks.

Hope this is of some help.

Roger

[les M]

Roger
Have you removed the pistons yet, if you have then what is the conidtion of the bores? After 3000 miles I think that the bores may not need to be fully honed but ony cleaned up. When you say that your engine was perfectly tuned, have you had it set up on a rolling road, what air/fuel ratio are you running at wide open throttle, how many degrees of maximum advance are you running and at what revs is maximum advance attchieved ?
Les.

[engineman]

An interesting question, I agree that in the good old days of 4 star petrol the difference was only 1 bhp but with the car runing with lead free petrol my feeling is that the high compression pistons will make a bigger difference, my experience at the rolling road day at Enginuity when a bog standard stag with H/C pistons produced nearly the same output as my heavily modified car also encouraged me to change them. I plan to write a full report when the car is on the road agian and has been tested again at Enginuity.

[surreyone]

An interesting question, I agree that in the good old days of 4 star petrol the difference was only 1 bhp but with the car runing with lead free petrol my feeling is that the high compression pistons will make a bigger difference, my experience at the rolling road day at Enginuity when a bog standard stag with H/C pistons produced nearly the same output as my heavily modified car also encouraged me to change them. I plan to write a full report when the car is on the road agian and has been tested again at Enginuity.

Hi,
Any idea when the Stag will be on the road?
I went to the first Enginuity open day and like you my car has holley and 4 branch and I found that standard cars with H/C pistons produced nearly the same power.
I await with INTEREST!!! Good luck.
Kind regards
Colin